Luis
M. CARRASCAL
Profesor de
Investigación
Dept. Biodiversidad y Biología Evolutiva
Museo Nacional de Ciencias Naturales
Consejo Superior de Investigaciones
Científicas
Lista completa de publicaciones
Carrascal,
L.M.;
Galván, I.; Gordo, O. 2009. Partial least squares regression as an
alternative to most currently used regression methods in Ecology. Oikos, 118:681-690 [SUMMARY]
[pdf]
Carrascal, L.M.; Seoane, J.; Palomino, D.; Polo,
V. 2008. Explanations
for bird species range size: ecological correlates and phylogenetic
effects in the
Seoane,
J.; Carrascal, L.M. 2008. Interspecific differences in population trends of
Spanish birds are related to habitat and climatic preferences. Global
Ecology & Biogeography 17:111-121. [SUMMARY] [pdf]
Polo, V.; Carrascal,
L.M.; Metcalfe, N.B. 2007. The effects of latitude and day length on fattening strategies of
wintering coal tits (Periparus ater L): a field study and aviary experiment. Journal
of Animal Ecology 76:866-872.
[SUMMARY]
[pdf]
Bosch, J.; Carrascal, L.M.; Durán, L.; Walker,
S.; Fisher, M.C. 2007. Climate change and outbreaks of amphibian chytridiomycosis in a montane
area of
Carrascal, L.M.; Polo, V. 2006. Effects of wing area reduction on
winter body mass and foraging behaviour in coal tits: field and aviary
experiments. Animal Behaviour 72: 663-672. [SUMMARY]
[pdf]
De
Carrascal, L.M.; Alonso, C.L. 2006. Habitat use
under latent predation risk. A case study with wintering forest birds. Oikos
112: 51-62 [SUMMARY] [pdf]
Seoane, J.; Carrascal, L.M.; Alonso, C.L. y Palomino, D. 2005. Species-specific traits associated to prediction errors in bird habitat suitability modelling. Ecological Modelling 185:299-308. [SUMMARY] [pdf].
Carrascal, L.M. 2004.
Distribución y abundancia de las aves en
Carrascal, L. M.; Lobo, J. L. 2003. Respuestas a viejas preguntas con
nuevos datos: estudio de los patrones de distribución de la avifauna española y
consecuencias para su conservación. Pp. 645-662 y 718-721 en Martí, R., Del
Moral, J.C. (Eds.). Atlas de las Aves
Reproductoras de España. Dirección General de
Belliure, J.; Carrascal. L.M. 2002.
Influence of heat transmission mode on heating rates and on the selection of
patches for heating in a Mediterranean lizard. Phys. & Bioch. Zool. 75(4):369-376. [SUMMARY] [pdf]
Carrascal, L.M.; Díaz,
J.A.; Huertas, D.L.; Mozetich,
Carrascal, L.M.; Polo, V. 1999. Coal tits, Parus
ater, lose weight in response to chases by predators.
Animal Behaviour 58:281-285. [SUMMARY] [pdf]
Polo, V.; Carrascal,
L.M. 1999. Shaping the body size distribution of passeriformes:
habitat use and body size are evolutionarily and ecologically related. Journal
of Animal Ecology. 68:324-337. [SUMMARY] [pdf]
Carrascal, L.M.; Senar,
J.C.; Mozetich,
Carrascal, L.M.; Díaz, M. 1998. Utilidad
científica y difusión internacional de Ardeola: un
análisis bibliométrico - Scientific
utility and international diffusion of Ardeola: a bibliometric analysis. Ardeola 45:221-239. [SUMMARY] [pdf]
Belliure, J.; Carrascal, L.M.; Díaz, J.A. 1996. Covariation of
thermal biology and foraging mode in two mediterranean
lacertid lizards. Ecology 77:1163-1173. [SUMMARY] [pdf]
Carrascal, L.M.;
Carrascal, L.M.; Moreno, E.; Valido, A.
1994. Morphological evolution
and changes in foraging behaviour of island and mainland populations of Blue
Tit, Parus caeruleus.
A test of convergence and ecomorphological hypoteses. Evolutionary Ecology 7:25-35. [SUMMARY] [pdf]
Tellería, J.L.; Carrascal,
L.M. 1994. Weight-density relationships between and within bird communities.
Implications of niche space and vegetation structure. American Naturalist
141:1083-1092. [SUMMARY] [pdf]
Moreno, E.; Carrascal, L.M. 1993. Leg morphology and feeding postures
in four Parus species: an experimental ecomorphological approach. Ecology 74:2037-2044. [SUMMARY] [pdf]
Díaz, J.A.; Carrascal, L.M. 1993. Variation in the effect of profitability on prey size selection by the lacertid lizard Psammodromus algirus. Oecologia (Berl.) 94:23-29. [SUMMARY] [pdf]
Carrascal, L.M.; López, P.; Martín, J.;
Salvador, A. 1992. Basking and
antipredator behaviour in a high altitude lizard:
implications of heat-exchange rate. Ethology
92:143-154. [SUMMARY] [pdf]
Carrascal,
L.M.;
Carrascal,
L.M.; Tellería, J.L.; Valido, A. 1992. Habitat distribution of canary
chaffinches among islands: competitive exclusion or species-specific habitat
preferences? Journal of Biogeography 19:383-390. [SUMMARY] [pdf]
Carrascal, L.M.; Tellería,
J.L. 1991. Bird size and density: a regional approach. American Naturalist
138:777-784. [SUMMARY] [pdf]
Díaz, J.A.; Carrascal, L.M. 1991.
Regional distribution of a Mediterranean lizard: influence of habitat cues and
prey abundance. Journal of Biogeography 18:291-297. [SUMMARY] [pdf]
Carrascal, L.M.;
Carrascal,
L.M.; Galván,
I.; Gordo, O. (accepted). Partial least squares
regression as an alternative to most currently used regression methods in
Ecology. Oikos, 118:681-690.
This paper briefly presents
the aims, requirements and results of partial least squares regression analysis
(PLSR), and its potential utility in ecological studies. This statistical
technique is particularly well suited to analyzing a large array of related
predictor variables (i.e., not truly independent), with a sample size not large
enough compared to the number of independent variables, and in cases in which
an attempt is made to approach complex phenomena or syndromes that must be
defined as a combination of several variables obtained independently. A
simulation experiment is carried out to compare this technique with multiple
regression (MR) and with a combination of principal component analysis and
multiple regression (PCA+MR), varying the number of predictor variables and
sample sizes. PLSR models explained a similar amount of variance to those
results obtained by MR and PCA+MR. However, PLSR was more reliable than other
techniques when identifying relevant variables and their magnitudes of
influence, especially in cases of small sample size and low tolerance. Finally,
we present one example of PLSR to illustrate its application and interpretation
in ecology.
Carrascal, L.M.; Seoane, J.; Palomino, D.; Polo,
V. 2008. Explanations for bird
species range size: ecological correlates and phylogenetic
effects in the
Aim To
explore the determinants of island occupancy of 48 terrestrial bird species in
an oceanic archipelago, accounting for ecological components while controlling
for phylogenetic effects.
Location The
seven main islands of the Canary archipelago.
Methods We
obtained field data on population density, habitat breadth and landscape
distribution in Tenerife, Fuerteventura and
Results The
two measurements of occupancy (number of occupied islands or 10 ·
Main conclusions The habitat-generalist species with a tolerance for novel urban
environments tend to be present on more islands and to occupy a greater area,
whereas large-sized species that are genetically differentiated within the
islands are less widespread. Therefore, some properties of the ranges of these
species are explicable from basic biological features. A positive relationship
of range size with local abundance, previously shown in continental studies,
was not found, probably because it relies on free dispersal on continuous
landmasses, which may not be applicable on oceanic islands.
Seoane, J.; Carrascal, L.M. (2007). Interspecific
differences in population trends of Spanish birds are related to habitat and
climatic preferences. Global Ecology & Biogeography 17:111-121.
1. Aim Animal monitoring programs have allowed analyses of population trends,
most of which recently comment on the possible effect of global climate change.
However, the relationship between the interspecific
variation in population trends and species’ traits such as habitat preferences,
niche breadth or distribution patterns have received little attention, in spite
of its usefulness in the construction of ecological generalizations. The
objectives of this study were to (1) determine whether there are characteristics
shared among species with upwards or downwards trends, and (2) assess whether
population changes agree with what could be expected under global warming (a
decrease of species typical of cooler environments).
2. Location The Spanish part of the Iberian Peninsula (ca. 500,000 km2) in
the south-western part of the Mediterranean Basin.
3. Methods We modelled recent breeding population changes (1996-2004), in areas
without aparent land use changes, for fifty-seven
common passerine birds with species-specific ecological and distributional
patterns as explanatory variables.
4. Results One-half of these species have shown a generalized pattern towards the
increase of their populations, while only one-tenth showed a significant
decrease. One half (54%) of the interspecific
variability in yearly population trends is explained considering
species-specific traits. Species showing more marked increases preferred wooded
habitats, were habitat generalists and occupied warmer and wetter areas, while
moderate decreases were found for open country habitats living in drier areas.
5. Main conclusions The coherent pattern in population trends we found
disagree with the proposed detrimental effect of global warming on bird
populations of Western Europe, which is expected to be more intense in bird
species inhabiting cooler areas and habitats. Such pattern suggests that
factors other than the increase in temperature may be brought to discussions on
global change as relevant components to explain recent changes in biodiversity.
Polo, V.; Carrascal, L.M.; Metcalfe, N.B.
(2007). The effects of latitude and day length on
fattening strategies of wintering coal tits (Periparus
ater L): a field study and aviary experiment. Journal
of Animal Ecology, 76:866-872.
1. Cyclic daily fattening routines are very common in wintering small wild
birds, and are thought to be the consequence of a trade-off between different
environmental and intrinsic factors. According to theory, these trajectories
should range from accelerated (i.e. mass increases exponentially towards dusk)
when mass-dependent costs are the most important cause of mortality, to
decelerated (i.e. the rate of mass gain is highest at dawn and decreases
afterward) when starvation is the greater risk.
2. We examine if geographically separate populations of coal tits,
wintering in Scotland and Central Spain under contrasting photoperiods, show
differences in their strategies of daily mass regulation. We describe
population differences in wild birds under natural conditions, and
experimentally search for intrinsic interpopulation
variation in diurnal body mass increase under common, manipulated, photoperiod
conditions (9 h Light:15 h Dark vs 7L:17D)
, controlling for temperature, food availability, predator pressure and
foraging arena.
3. Winter diurnal mass gain of wild coal tits was more delayed towards the
latter part of the daylight period in Central Spain (i.e., the locality with longer
winter days) than in Scotland. In both localities, the pattern was linked to
the average mass at dawn, with mass increasing more rapidly in lighter birds.
However, under the controlled photoperiod situation the pattern of daily mass
gain was similar in both populations. Diurnal body mass gain was more
accelerated at the end of the day, and the increase in body mass in the first
hour of the day was considerably lower under the long (9 hours) than under the
short (7 hours) photoperiod in both populations.
4. Wintering coal tits show patterns of mass gain through the day that are
compatible with current theories of the costs and benefits of fat storage, with
birds at lower latitudes (with longer winter days) having a greater tendency to
delay mass gain until late in the day. The experimental study revealed that
these patterns are plastic, with birds responding directly to the photoperiod
that they experience, suggesting that they are continually making fine-scale
adjustments to energy reserves on the basis of both intrinsic (e.g.
state-dependent) and extrinsic cues.
Bosch,
J.; Carrascal, L.M.; Durán,
L.; Walker, S.; Fisher, M.C. (2007).
Climate change and outbreaks of amphibian chytridiomycosis
in a montane area of
Amphibian
species are declining at an alarming rate on a global scale in large part due
to an infectious disease caused by the chytridiomycete
fungus, Batrachochytrium dendrobatidis. This pathogen of amphibians has recently
emerged within
De
1. Land owners in some European
Mediterranean regions receive subsidies to thin dense maquis.
This practice consists in the elimination of most shrubs and saplings and the
pruning of the tallest trees to favour more opened woodland stands. We
investigated how this practice affects the structure of bird communities. 2. We
designed a large scale ‘natural experiment’ that included 21 paired thinned and
un-thinned maquis stands in
Seoane, J.; Carrascal, L.M.; Alonso, C.L. y
Palomino, D. (2005). Species-specific traits associated
to prediction errors in bird habitat suitability modelling. Ecological
Modelling 185:299-308.
Although
there is a wide range of empirical models applied to predict the distribution
and abundance of organisms, we lack an understanding of which ecological
characteristics of the species being predicted affect the accuracy of those
models. However, if we knew the effect of specific traits on modelling results,
we could both improve the sampling design for particular species and properly
judge model performance. In this study, we first model spatial variation in
winter bird density in a large region (
Carrascal, L.M.; Polo, V. (2006). Effects
of wing area reduction on body mass and foraging behaviour in the coal tit (Parus ater) during
winter: field and aviary experiments. Animal Behaviour 72: 663-672.
Theoretical and experimental evidence suggests
that an increase in flight costs will cause a decrease in flight performance,
and that birds should trade-off the benefits of body reserves to minimize these
costs. However, an alternative strategy could be to avoid the dangers of starvation
by increasing food intake, thereby maintaining body reserves, and/or decreasing
flight activity to compensate for the greater per unit flight costs. To test
the effect of increased flight costs on body mass regulation and on flying and
feeding activity, we experimentally manipulated wing area in a free-ranging
wintering population of coal tits (Parus ater), and in captive birds living in a less
restrictive environment (large outdoor aviaries). In the field, there was a
clear trend towards body mass decrease when wing area was experimentally
reduced, although it was not homogeneous: heavier birds lost more weight than
lighter birds as a consequence of an allometric
increase in flying costs. However, the experimental reduction of wing area had
a non-significant, negligible, effect on body mass in the aviaries. Flight and
feeding frequency were significantly affected by the experimental reduction of
wing area: birds flew less and ate more when wing area was reduced. Birds with
higher wing loads decreased more markedly flying frequency when wing area was
reduced. We suggest that the goal of small
resident birds living in Mediterranean montane
climate would be to maintain daily fat reserves within some narrow limits
during autumn and winter, even under contrasting ecological conditions. Our results show a trade-off between
wing area reduction and body mass (in the field) and a trade-off between wing
area and flying frequency (in the aviaries), both mediated by allometric effects of body size.
Carrascal, L.M.; Alonso, C.L.
(2005). Habitat use under latent predation risk. A case
study with wintering forest birds. Oikos 112: 51-62
We test the prediction that
predation risk is a foraging cost affecting the spatial distribution of birds
within habitat. The work was carried out in a montane
mixed
BELLIURE, J.; CARRASCAL. L.M. (2002). Influence of heat
transmission mode on heating rates and on the selection of patches for heating
in a Mediterranean lizard. Phys. & Bioch. Zool. 75(4):369-376.
Heliothermy (heat gain by radiation) has been given a
prominent role in basking lizards. However, thigmothermy
(heat gain by conduction) could be relevant for heating in small lizards. To
ascertain the importance of the different heat transmission modes to the
thermoregulatory processes, we conducted an experimental study where we
analyzed the role of heat transmission modes on heating rates and on the
selection of sites for heating in the Mediterranean lizard Acanthodactylus
erythrurus (Lacertidae).
The study was conducted under laboratory conditions, where two situations of
different operative temperatures (38° and
CARRASCAL, L.M.; DÍAZ, J.A.;
HUERTAS, D.L.; MOZETICH, I. 2001. Behavioral thermoregulation by treecreepers: trade-off
between saving energy and reducing crypsis. Ecology
82:1642-1654.
We
studied the effect of solar radiation on the winter biology of Short-toed Treecreepers Certhia brachydactyla inhabiting a montane
coniferous forest. We hypothesized that, in temperate latitudes of cold winter
climate with low cloudiness and under windless conditions, birds should select
sunlit sites (i.e., forest sectors or trunk patches with high levels of
exposure to sunlight) to reduce the metabolic cost of thermoregulation. At a
within-habitat scale, a hypothesis of "only metabolic benefits"
predicts that birds should select sunlit patches at temperatures in the shade (Tshade) below the lower critical
temperature (Tlc), and shift to a
random use of sunlit and shaded patches at temperatures above Tlc. Alternatively, there could be added
costs (e.g. travel costs, predation risk) to the use of sunlit patches. If
higher visibility leads to diminished crypsis at
sunlit patches ("trade-off with predation risk hypothesis"), birds
should select only shaded patches at Tshade
values above Tlc (to enhance crypsis), and their selectivity for sunlit patches should
gradually increase as Tshade
decreases below Tlc.
Treecreepers were selective in their use of sun-shade
patches. This result holded at different spatial
scales. At the between-plots scale (habitat preferences across different forest
tracts), the abundance of treecreepers was positively
related to the availability of sunlit trunks when holding for the effects of
tree density, prey availability, and altitude. At the within-plot scale
(selection of foraging patches on trunks and thick branches), Ivlev’s electivity for sunlit patches decreased linearly as
Tshade increased. Birds preferred
to forage on sun exposed surfaces (electivity > 0) when Tshade
was lower than »
Photometric
measurements of treecreeper taxidermic
mounts realistically positioned on trunk surfaces, and detection times by
simulated (human) predators, suggest that treecreepers
were more detectable under direct solar radiation than in deep shade. Crypsis diminished in sunlit patches because of a higher
image contrast, and an increased difference in perceivable coloration between
bird and background, relative to shaded patches. Average detection times were
significantly lower for sunlit mounts. Moreover, focal birds scanned more
frequently in sunlit than in shaded patches. Thus, the observed temperature
dependent variation in the selection of sunlit substrata is consistent with the
"trade-off with predation risk hypothesis" predicting that prey
should avoid patches where they are more detectable to potential predators. We
interpret the distribution and behavior of treecreepers as indicative of a trade off between the
energy savings (due to higher operative temperature and reduced metabolic
costs) and the increased risk of predation (due to higher visibility and
diminished crypsis) afforded by sunlit foraging
patches.
POLO, V.; CARRASCAL, L.M. 1999. Shaping the body
size distribution of passeriformes: habitat use and
body size are evolutionarily and ecologically related. Journal of Animal
Ecology 68:324-337.
The
effect of habitat structure on the distribution of the number of species by
body size classes has been analysed with the Passeriforms
of the Western Palearctic.
Evolutionary
history of the group accounted for 68% of the interspecific
variation in body mass. The phylogenetic effect is
highly significant from the most recent evolutive
radiations (i.e. genera) towards more ancient radiations (i.e. parvorders). In a more fine-grained study with a subset of
55 passerine species living in
Throughout
the evolutionary history there has been a considerable concentration of species
around 10-
Removing
the effect of evolutionary history on present-day variation in body mass
(specific component of the phylogenetic
autoregressive method), the distributions of body mass of open country and
woodland species are markedly different: species from woodland habitats are
lighter (mainly due to the large frequency of small-sized species) and their
body masses are less concentrated than in species from open country habitats.
Results for the phylogenetic component are similar to
those of the specific component.
Habitat
use was strongly correlated with body mass in a subset of 55 species living in
These
results show that the evolutionary history of Western Palearctic
Passeriforms has not produced neutral variation in
body mass with respect to habitat preferences and habitat use, and supports the
view that macro and micro processes have not been decoupled in the evolution of
body size.
CARRASCAL, L.M.; SENAR, J.C.; MOZETICH,
Body
condition and feather growth rate of Great Tits (Parus
major) were studied in relation to dominance in two contrasting
Mediterranean localites during late autumn and early
winter. The two localities differed in altitude, ambient temperatures (100 vs
Percentage
of time spent at feeders was higher at El Ventorrillo
(the locality with colder climate and less natural food availability), and was
associated with dominance only in this locality. Number of aggressive displacements
per hour suffered by each individual was higher (150-fold greater) in the area
with less arthropod availability and lower temperatures. Protein reserves
measured as pectoralis muscle thickness was higher at
El Ventorrillo, and was positively and consistently
related to dominance in both localities. Growth rate of induced feathers was
slower in the locality that was colder and had less natural food availability
(El Ventorrillo), but was not clearly and directly
related to dominance in both localities. Only dominant adult males in El Ventorrillo could compensate the higher environmental
harshness of this locality attaining a higher feather growth rate than the
other sex-age classes. Feather mass asymmetry during autumn was not associated
with body condition, did not change between localities, and was inversely and
consistently related to dominance in both localities. The covariation
pattern among variables describing bird size, access to supplemented food, body
condition, feather growth rate and asymmetry was different in both localities.
Only in the locality with colder temperatures and lower arthropod food
availability (El Ventorrillo) larger, more dominant,
Great Tits spent more time foraging on feeders, had a thicker pectoralis muscle (i.e. body condition), and grew
the induced feathers at a higher rate.
MORENO, E.; BARBOSA, A.;
CARRASCAL, L.M. 1997. Should congruence
between intra- and interspecific ecomorphological
relationships be expected? A case study with the Great Tit Parus
major. Proceedings of The Royal Society
We
studied the relationships between leg morphology and feeding posture while
feeding in a population of Great Tit (Parus
major) under controlled conditions to investigate to what extent morphology
and ecology are linked at the individual level. From predictions generated at
the interspecific level within the genus Parus (Moreno & Carrascal 1993, Ecology
74:2037-2044), we test
whether interspecific and intraspecific
ecomorphological relationships are consistent.
The
slopes of the regressions of the leg length segments are significantly lower
than those expected under isometry (geometric
similarity). For IMI distance (distance from the head of the fibula to the
insertion point of the iliofibularis muscle) and IMT
distance (distance from the head of the tibiotarsus
to the insertion point of the tibialis cranialis muscle) the regression slopes are not higher than
those predicted by isometry (for IMI distance the
slope is even significantly lower than that expected; p<0.001). The
regression slopes of the muscular forces of M. iliofibularis
and M. tibialis cranialis
do not significantly differ from those expected under isometry.
Therefore, only for leg length segments deviations from an isometric
relationship with body mass are big enough to allow the emergence of ecomorphological patterns. Combining the coefficients of
deviation from the geometric similarity there is no sufficient morphological
variation between individuals to promote clear associations between morphology
and hanging performance (apart from that expected by geometric similarity due
to interindividual differences in body size). Thus,
we should not expect significant relationships between leg morphology and
average time spent hanging.
Within
our population, neither leg bone lengths nor leg muscle morphology were related
to the feeding posture of individuals. However, differences in body weight were
correlated with inter-individual differences in time spent hanging. These
results demonstrate that the association between intraspecific
and interspecific ecomorphological
relationships is not uniform. We argue that at the intraspecific
level body weight overrides the significance of other traits that have a
functional meaning at interspecific level (i.e.,
leg segment lengths, muscular morphology), due to isometric variation of
morphological traits (muscular and squeletal) with
body mass. Thus, the discrepancy between the ecomorphological
associations at interspecific and intraspecific
levels is the result of a problem of scale (morphological changes in
evolutionary time and isometric variation of morphological traits with body
mass in ecological time).
BELLIURE, J.; CARRASCAL, L.M.; DÍAZ, J.A. 1996. Covariation
of thermal biology and foraging mode in two mediterranean
lacertid lizards. Ecology 77:1163-1173.
Body
temperatures, heat exchange rates, behavioral
thermoregulation, and movement behavior (as an index
of foraging mode) were studied in two widely distributed, medium sized lacertid lizards (Acanthodactylus
erythrurus and Psammodromus
algirus). Psammodromus
algirus mainly inhabits broad-leaved forests,
while A. erythrurus prefers open sandy areas
with sparsely distributed vegetation. These habitat preferences parallel
differences between the areas in which both genera presumably originated: Eurosaharian xeric steppes with high operative temperatures
(Te’s) for Acanthodactylus,
and
Field
observations showed that percentage of time spent basking and basking rate (no.
of basks per minute) were negatively related to Te, although average
bask duration was not. Percentage of time spent moving, moving rate (no. of
moves per minute), and the average duration of individual moves were inversely
related to Te, and were higher in P. algirus.
The percentage of total locomotion time that was spent moving in the shade was
also higher in P. algirus. Behavioral
thermoregulation strategies differed between both species in a laboratory thermogradient where P. algirus
basked more often and for shorter periods, and selected warmer patches, than A.
erythrurus. Selected body temperatures (Tb’s)
in a laboratory thermogradient were significantly
higher in A. erythrurus than in P. algirus. Shade Seeking Tb was higher
in A. erythrurus, while Resume Basking Tb
did not differ significantly between the two species. Heating and cooling rates
were also different in the two species: A. erythrurus
warmed more slowly, and cooled faster, than P. algirus.
Our
data support the existence of a complex syndrome which combines aspects of the behavior, physiology, and ecology of both species, so that
the thermal consequences of inhabiting a certain type of habitat can be
counterbalanced by behavioral and physiological means
that, in turn, affect movement (and hence foraging) behavior.
Thus, the more active species (P. algirus)
heated faster, cooled more slowly, and basked more often but for shorter
periods and at warmer patches than the less active one (A. erythrurus).
CARRASCAL, L.M.; MORENO, E.; VALIDO, A. 1994. Morphological
evolution and changes in foraging behaviour of island and mainland populations
of Blue Tit, Parus caeruleus.
A test of convergence and ecomorphological hypoteses.
Evolutionary Ecology 7:25-35.
We
study the leg morphology and feeding postures of two subspecies of Blue Tit (Parus caeruleus;
Island
Blue Tit has longer tarsometatarsus, larger foot span,
and a more proximal insertion of tibialis cranialis muscle (flexor of the tarsometatarsus)
than the mainland Blue Tit. These morphological differences are consistent with
the more frequent use of hanging and clinging head-up postures by the Iberian Blue
Tit. Several ecomorphological hypotheses obtained at interspecific level with other taxa,
have proved to be of high predictive value for explaining ecological
differences considering morphological evolution. Tenerife Blue Tit and Iberian
Coal Tit clearly show close convergence in both feeding postures and leg
structure, although some differences in morphology were found between these two
species. Convergence in foraging methods between island Blue Tit and mainland
Coal Tit can be explained without considering current interspecific
competition as a determinant of niche space.
TELLERÍA, J.L.; CARRASCAL, L.M. 1994.
Weight-density relationships between and within
bird communities. Implications of niche space and vegetation structure. American
Naturalist 141:1083-1092.
The
population density of a species in a given area is limited by the number of
individuals that the area can support, equivalent to the amount of energy available
to the population divided by the energetic requirements per individual of each
species. Some studies have attempted to evaluate this capacity rule by
examining the inverse relationship between density (D) and body weight (W) in
several animal groups using the equation D=aWb.
We
develop two different analyses that compare bird communities on two distinct
spatial scales. The first approach incorporates information on foraging behavior to analyze body weight-density relationships
within different assemblages (according to substrate use). This is a large
scale comparison that emphasizes similarities among forest bird communities in
widely different forest habitats across two continents; species from different
habitats and continents are assigned to the same set of foraging assemblages.
The second analysis compares communities of forest birds in the same geographic
region, analyzing the allometric relationship of
population density for all species in the same community. The results are
compared across a systematically varying environmental gradient (foliage
volume).
To
analyze the relationship between mean body weight of assemblages and rate of
density change with bird size, we reviewed studies on bird use of space during
the breeding season in five woodland communities of North America and in two of
Mean
body weight of assemblages decreased as thinness and pliability of foraging
substrates increased. The relationship between density and body mass within
each assemblage, as shown by slopes from allometric
equations (b), gave an inverse association with thinness of foraging substrates
(log-log correlation: r=0.51, n=28). Slope b was positively correlated with
mean weight (weighted by density) of birds in each assemblage; i.e., the
lower the body weight of birds in assemblages, the more negative the slope of
the allometric regression of D on W. These results
support the view that bird assemblages show varying relationships between
density and species' body weight within the niche space of communities.
Analysis
at the community level provided similar results. Average weight (weighted by
density of each species) of bird communities decreased with increasing
foliage-volume index (log-log regression: r=-0.704, p=0.002, n=17). Slopes of the
allometric regressions of D on W (b) were inversely
and significantly correlated with the foliage-volume index (log-log model:
r=-0.761, p=0.0004, n=17), and directly associated with average weight of bird
communities (log-log model: r=0.613, n=17; significance not provided due to
partial dependence between b and W).
Correlation
coefficients between body weight and maximum ecological density was
The
W-D relationships, as measured by b, suggest that larger species are able to
gain resources in proportion to their size, whereas smaller species have more
equitable resource allocations, and so show the expected D-W associations. The
results provided by this paper illuminate the previously contrasting patterns
obtained about resource extraction by species within communities. The confusing
patterns of the D-W relationships that are so frequently observed in birds
could be at least partly due to the use of bird densities obtained from
habitats that, because of their different structure, provide different niche
opportunities to species of different sizes. Therefore, a more autecological approach ought to be employed in the analysis
of allometric relationships linking body weight to
density.
MORENO, E.; CARRASCAL, L.M. 1993. Leg morphology and feeding postures
in four Parus species: an experimental ecomorphological approach. Ecology 74:2037-2044.
We
investigate the ecomorphology of four phylogenetically closely related species of Parus (P. major, P. caeruleus,
P. cristatus, and P. ater)
that cooccur in a mixed Mediterranean woodland of
The
relative length of the leg (femur + tibiotarsus + tarsometatarsus lengths) differed significantly among tit
species, Blue and Great Tits having shorter legs than Crested and Coal Tits.
Significant differences were also found in tarsometatarsus
length with Great and Blue Tits having shorter tarsometatarsus
than that of Coal and Crested Tits. The insertion of the M. tibialis
cranialis onto the cranial surface of the tarsometatarsus is proportionally more distal in the Blue
Tit than in the other three Tits.
Our
results demonstrate that all tit species studied are able to use hanging and
standing postures. However, there exist differences in the
"preferred" foraging postures among the four Parus
species. The Blue Tit used hanging in a higher proportion than the other three Parus species; the Crested Tit spent the lowest proportion
of time hanging. The Blue Tit and the Crested Tit also showed the most
contrasting hindlimb morphological designs. The
ranking of the four tit species according to hanging frequency is consistent
with the predicted order derived from morphofunctional
hypotheses (including muscles iliotibialis cranialis, gastrocnemius, fibularis brevis, and tibialis cranialis, relative
length of legs, and body mass).
Blue
Tit is the species with shortest legs. It has the main flexor muscles of the
hip and intratarsal joints (M. iliotibialis
cranialis and M. tibialis cranialis respectively) modified in the direction that
increases the force of their action (i.e., closing the joints). M. fibularis brevis is also modified
to strengthen its action maintaining the tarsometatarsus
at its position once it is flexed. Pars interna of M.
gastrocnemius, the main extensor of the ankle, is, on
the contrary, partially atrophied in the Blue Tit. This morphological pattern
fits the mechanical requirements for hanging; i.e., morphological design should
tend to counteract the force of gravity (the main force acting upon the bird
while hanging) which pulls the body downwards and tends to open the leg joints.
Conversely, the Crested Tit has the longest legs. The main extensor muscle of
the ankle, M. gastrocnemius, is modified by the
addition of extra fibers to its pars interna, increasing ankle extension, as the force exerted
by a muscle is related to its number of fibres. Leg flexor muscles are not as
well developed as in the Blue Tit (decreased leg flexion power). This hind limb
morphology better fits the mechanical requirements for standing; i.e.,
morphological design should tend to counteract the force of gravity, which,
while standing, tend to close the leg joints. It is plausible to hypothesize an
unspecialized postural selection as the primitive behavioural character state
for Parus.
CARRASCAL, L.M.; TELLERÍA, J.L.;
VALIDO, A. 1992. Habitat distribution of canary
chaffinches among islands: competitive exclusion or species-specific habitat
preferences? Journal of Biogeography 19:383-390.
The
habitat distribution between-islands of Common Chaffinch (Fringilla
coelebs L.) related to the presence of the
potential competitor species Blue Chaffinch (Fringilla
teydea Moquin-Tandon),
has been studied in the Canary Islands (
The
habitat selection pattern observed in Hierro was
congruent with that obtained for the continental subspecies at the North of the
CARRASCAL, L.M.; TELLERÍA, J.L. 1991. Bird
size and density: a regional approach. American Naturalist 138:777-784.
Within
groups of taxonomically-related, ecologically similar organisms, large
individuals demand more from environmental resource pools than small ones, but
also tend to occur at lower densities. Some studies have proved the inverse
relationship between weight (W) and density (d) in several
zoological groups. This relationship is well fitted to the equation d=aWb (log(d) = log(a)+b·log(W)), where d and W are normally
obtained from bibliographical reviews. This relationship is unsatisfactory in
the case of birds apart from raptors, although there has been no convincing
explanation of this result. We review several aspects responsible of this lack
of association.
Densities
may be classed as regional densities (dreg) when referring to density
reached by species in a region which includes diverse types of habitats, and
ecological densities (di) when referring to a
defined habitat (common approach in studies on communities of small
vertebrates). The maximum ecological density (dmax)
places each species at its most optimum habitat in the area. It may be obtained
from an analysis of di distribution in the
study area. According to animal distribution models, these habitats should be
the first to be saturated when the regional population level increases. This
situation favours size-dependent restrictions to animal abundance. The use of dmax attenuates the distorting effect of habitat
preferences. The correlation between dmax and W
will thus be better than that obtained using a random selection of ecological
densities (di) of each species in any of the
regions' habitats, as it is usually done. On the other hand, given that dreg
attenuates the potential distorting effect of the high variability of random
selected di values by weighing the regional
significance of each habitat in species abundance, it will foreseeable
correlate better with W.
In
this paper we investigate the relationship between d and W in small
insectivorous birds of the Basque Country (North of Spain). Ecological
densities (di) were estimated using line
transects in the 10 most extensive habitats of the region. While this method
does not completely reduce the effects of differences in species detectability, it is considered adequate for an approximate
characterization of small passerines and related species densities. Attention
was thus centered on 47 species weighing between 6 (Regulus ignicapillus)
and
The
relationship between di and W for all
species and habitats showed a "polygon" of points in which each
interval of W (similar sized species) provided a high variability of
values of di. The upper profile of
this polygon descended as W increased, corresponding to the maximum densities (dmax) of each species, while the lower profile was
parallel to the axis of X (lower densities). The mean result from the
correlations among random selected di for each
species (null model) in this "polygon" show that r=-0.217 with 19
mean degrees of freedom. The confidence interval is from -0.332 to -0.102 at 1%
and -0.305 to -0.129 at 5%.
Using
the regression analysis of W on dmean, dmax and dreg for the 47 species we obtained
that the correlations were negative and the value of r exceeded that from the
null model. The use of the dmax thus seems to
improve the relationships between d and W (b=-0.62; explained
variation: 25.14%). The results of this study demonstrate a negative
relationship between d and W in small insectivorous birds, and
that it is important to consider the variability of densities due to the uneven
distribution of the species by habitats. The similarity between the absolute
values of our coefficients b and those derived from energetic allometric equations (b=0.75) seems to point out to the
idea that the amount of energy used by these small insectivorous birds is
independent of their body size.
DÍAZ, J.A.; CARRASCAL, L.M. 1991. Regional
distribution of a Mediterranean lizard: influence of habitat cues and prey
abundance. Journal of Biogeography 18:291-297.
We
analyzed the local variations in the relative abundance of a common
Mediterranean lizard species, Psammodromus algirus (L.)
The
lack of significant correlation between the abundance of P. algirus and the scores on the climatic gradient (CPC)
indicates that mesoclimate is not truly important for
the distribution and abundance of this lizard species. The presence of other lacertid species seemed to be unrelated with the distribution
and abundance of P. algirus at a regional
scale. The effects of plant taxonomy on the abundance of P. algirus vanished with the exclussion
of other environmental attributes that appeared to be more important for the
biology of the species. This result showed that floristic gradients covariating with the abundance of P. algirus
did not have true causal effects but merely reflected underlying biological
processes.
Nevertheless,
a single structural component (the development of the low shrub canopy) accounted
for more than two thirds of the variance observed in the abundance of P. algirus. The underlying bases for this relationship are
two basic requirements of lizard biology: thermoregulation and predator
avoidance. Low shrub cover above
Despite
the high summer abundance of arthropod prey in Mediterranean environments,
their availability influenced the abundance of P.algirus
along a gradient of habitats over the main effects attributable to habitat
structure, since the partial correlation obtained was highly significant
(r=0.667, p=0.0025). The intriguing effect of food abundance on lizard
population levels could be interpreted as the consequence of a trade-off
between the conflicting demands of getting enough food and avoiding the
numerous predators that feed on P. algirus.
The
habitat selection patterns obtained were validated by means of jacknife and randomization procedures. Predicted and
observed values of lizard density were significantly and highly correlated.
CARRASCAL, L.M.; POLO, V. 1999. Coal
tits, Parus ater,
lose weight in response to chases by predators. Animal Behaviour 58:281-285.
Theoretical
models predict that birds should decrease their body mass in response to
increased predation risk because lighter birds take off faster and are more
manoeuvrable. We studied the effect of predation risk by chasing coal tits in
large outdoor aviaries thus simulating an attempt to capture them. With this
increase in predation risk, both perceived and actual, coal tits lost
significantly more weight than in a control situation when they were not
pursued. This pattern was attributable to a smaller gain in weight only during
the day; nocturnal weight did not change in relation to diurnal predation risk.
The lower daily weight gain was not consistent with predictions from models of
interrupted foraging, but was consistent with predictions from risk adjustment
models. Moreover, there was no difference in weight gain over 2-h periods that
included a 1-h fast and those in which feeding was ad libitum,
suggesting that coal tits could easily regain their body mass after a predator
had interrupted their feeding. Our results therefore suggest that pursuit by
predators leads to a decrease in the body mass of small birds.
DÍAZ, J.A.; CARRASCAL, L.M. 1993. Variation in the effect of
profitability on prey size selection by the lacertid
lizard Psammodromus algirus.
Oecologia (Berl.)
94:23-29.
Maximizing
the average rate of energy intake (profitability) may not always be the optimal
foraging strategy for ectotherms with relatively low
energy requirements. To test this hypothesis, we studied the feeding behaviour
of captive insectivorous lizards Psammodromus
algirus, and we obtained experimental estimates
of prey mass, handling time, profitability, and attack distance for several
types of prey.
Handling
time increased linearly with prey mass and differed significantly among prey
types when prey size differences were controlled for, and mean profitabilities differed among prey taxa,
but profitability was independent of prey size. The attack distance increased
with prey length and with the mobility of prey, but it was unrelated to
profitability. Thus, lizards did not seem to take account of the rate of energy
intake per second as a proximate cue eliciting predatory behavior.
This
information was combined with pitfall-trap censuses of prey (in late April,
mid-June and late July) that allowed us to compare the mass of the prey
captured in the environment with that of the arthropods found in the stomachs
of sacrified free-living lizards. In April, when food
abundance was low and lizards were reproducing, profitability had a pronounced
effect on size selection and lizards selected prey larger than average from all
taxa except the least profitable ones. As the active
season progressed, and with a higher availability of food, the number of prey
per stomach decreased and their mean size increased. The effect of
profitability on size selection decreased (June) and eventually vanished
(July-August). This variation is probably related to seasonal changes in the
ecology of lizards; e.g. time minimization in the breeding season as a
means of saving time for nonforaging activities versus
movement minimization by selecting fewer (but larger) prey in the postbreeding season. Thus, the hypothesis that maximizing
profitability could be just an optimal strategy for a terrestrial ectothermic vertebrate was supported by our data.
CARRASCAL, L.M.; DÍAZ, M. 1998. Utilidad científica y difusión
internacional de Ardeola: un análisis bibliométrico - Scientific
utility and international diffusion of Ardeola: a bibliometric analysis. Ardeola
45:221-239.
[pdf]
The
editorial line of Ardeola has been improved
from 1983 onwards to enlarge its scientific utility and international presence.
We analyse the pattern of citation of the papers published by Ardeola between 1983 and 1996 according to the
authors who citated them, to the reseach
topics these papers dealt with, and to the use of the scientific literature by
their authors. In addition, we compare these patterns with the patterns of
citation of ornithological papers published by Spanish scientists in
international journals included in the Journal Citation Reports (JCR). Patterns
of citation of papers published in low-citation journals (SCI<0.5) and
top-citation journals (SCI>1.5) were analysed separately. Our main objective
was to evaluate to what extent the goal of enlarging the international
diffusion and scientific utility of Ardeola,
which has directed the editorial line of the journal for the last two decades,
has been reached. Also, we tried to detect the main factors which could have
delayed reaching that goal, as well as to derive efficient ways to overcome
them.
The
average impact factor (SCI) of Ardeola
(computed as the number of citations received in a given year by the papers
published during the two previous years both in Ardeola
and in the JCR journals, divided by the number of papers published in Ardeola during the same time period) has been 0.26
citations/year. This impact factor was six times lower that the impact factor
of the ornithological papers published by Spanish scientists in top-citation
journals, but it was not significantly different from the impact factor of the
papers published by Spanish ornithologists in low-citation journals (0.31
citations/year on average). The impact factor of Ardeola
has decreased markedly along the study period. This fact was due to the
decreasing citation of Ardeola within Ardeola itself (71% autocitation
on average, that decreased from 87% to 47%). Low citation rates combined with a
short half-life of the papers published in Ardeola
(5.8 years). These results indicate that Ardeola
has had a low scientific utility and a narrow international relevance.
Most
citations of the papers published in Ardeola
came from their own authors and, to a much lesser extent, from other Spanish
scientists. Ardeola has been barely used by foreing scientists. These patterns differed markedly from
the citation patters of the papers published by Spanish scientists in
top-citation journals since the rate of citation of these papers by foreign
researchers was quite large, but they were nearly the same as the patters of
citation of the papers published by Spanish ornithologists in low-citation
journals (only the rate of autocitation was
marginally lower for Ardeola papers). Hence,
the use and diffusion of the papers published by Spanish scientists was not
improved substantially by the publication of these papers in low-citation
journals as compared to Ardeola.
Ardeola was very useful for the Spanish scientists, as
indicated by the high citation of Ardeola
papers that was found in the papers published by such scientists in
top-citation journals (1.1% of 3700 references in 89 papers). However, these
citations were too delayed from the date of publication of the papers in Ardeola (6.77 years on average), so that they did
barely contribute to the impact factor of the journal.
We
detected three main factors that contributed to explain the low scientific
usefulness and the narrow international diffusion of Ardeola:
(1) the research topics most papers published in Ardeola
dealt with, (2) the unappropriate use of the scientific
literature by their authors, and (3) the low scientific production of most
authors who have published in Ardeola.
Most
papers published in Ardeola in 1983-1995
(51.3%; n=249) have been descriptive studies focused on selected traits
of the basic natural history of one or few bird species; most of these studies
were not developed conceptually from its descriptive focus to address more
general topics, ideas or theories, and this fact has limited its citation by
other authors. As regards to the use of the scientific literature, the authors
who have published in Ardeola have tended to
employ few references (30.8 on average) from old sources (10.2% of the
references were published during the two years preceeding
the date of publication of the paper in Ardeola)
of low diffusion and international use (32.2% were references to JCR journals);
these facts have hampered both the conceptual development of the papers and its
possibilities of citation. Finally, more that half of the 271 authors who have
contributed to Ardeola in 1985-1996 have
published only one paper in this journal. Out of these 271 authors, 87.1% did
not publish any paper in international journals. On the other hand, most
authors of papers published in top-citation journals did not publish any paper
in Ardeola. Hence, Ardeola
has not been capabel to attracted (it has rather
repelled) authors of high scientific production, either Spanish or foreigners,
who could have contributed a great deal to the international diffusion of the
journal.
The
scientific utility of Ardeola lies at present
within the international ornithological journals of low impact factor. Hence,
there is no reason (no bibliometric reason at least)
for the current exclusion of Ardeola from the JCR
list. There is no reason either for the current lack of consideration of Ardeola papers when evaluating the scientific
production of their authors. However, Ardeola
has been affected by some factors which have limited its usefulness and
international diffusion. It is urgent to correct them in order to reach the
goal of enlarging such usefulness and difussion,
approaching at least the level already reached by the Spanish scientists who
have published its work in top-citation journals. Apart from implementing
efficient publicity campaigns and easy ways for consulting the contents of Ardeola (updated inclusion in databases of wide
diffusion such as Current Contents, web pages, etc.), it is necessary to
increase the consideration of Ardeola as an
option for publication for high-level authors (inclusion of review and forum
sections within the journal, rapid publication of manuscripts, etc.), as well
as to support preferentially those novel authors whose prospects for future
research and scientific production were better. Last, but by no means least, it
is urgent to promote an use of the literature by prospective authors as updated
and appropriate as possible, approaching it to the current use of the
literature displayed by the international scientific community. This editorial
policy is aimed at contributing to improve the conceptual elaboration of the
papers published in Ardeola, thus also
improving its potential utility and international diffusion.
Carrascal, L.M.; Moreno, E.; Mozetich,
I. 1995. Ecological plasticity of morphological designs.
An experimental analysis with tit species. Canadian Journal of Zoology
73:2005-2009.
To
determine whether behavioural plasticity in foraging modes is contingent upon
the phenotype of the species, we analyze the frequency of use of foraging
postures (standing vs hanging) under the
selection pressure of predation risk, of two contrasting tit species in leg
morphology (Blue Tit, Parus caeruleus, and Crested Tit, P. cristatus).
Results demonstrated that leg morphology of the Blue Tit enables it with
greater ecological flexibility in foraging postures than that of the Crested
Tit. The constrained foraging posture was to hang. Observed interspecific
differences in ecological flexibility are not attributable to interspecific differences in morphological variability
within species. Morpho-functional bases of ecological
flexibility in foraging postures are discussed. Morphological design may be
considered as an important factor in explaining niche width and potential for
niche shifts, as morphology might determine the range of ecological
"space" within which a species is allowed to move.
Carrascal, L.M.; Moreno, E.; Tellería,
J.L. 1990. Ecomorphological
relationships in a group of insectivorous birds of temperate forests in winter.
Holarctic Ecology 13:105-111.
We
examined the relationships between morphology and foraging behaviour in a group
of insectivorous birds wintering in temperate mixed forests in northern
Carrascal, L.M.; Moreno, E. 1992. Proximal
costs and benefits of heterospecific social foraging
in Great Tit Parus major. Canadian Journal of
Zoology 70:1947-1952.
The
feeding and vigilance schedules of Great Tits (Parus
major) at artificial feeders were studied in winter. We compared the
behaviour of birds that foraged in pars ( mono- or hetero-specific) and
solitarily. The percentage of time spent foraging was higher when a Great Tit
was with an individual belonging to a subordinate species rather than with
another Great Tit or a member of the dominant species. When a bird was
solitary, time spent foraging was less than when it was with an individual
belonging to a subordinate species, and greater than when it was with one
belonging to the dominant species. The proportion of time spent vigilant did
not differ between Great Tits that foraged with an individual from a dominant
species or a subordinate species or with a conspecific,
but was higher for solitary birds. Our results indicate that not all species
gain advantages by foraging in heterospecific dyads.
Individual Great Tits benefited from the presence of Coal, Blue, and Crested
tits, both by a lengthening of the time spent foraging at feeders, and by
conversion of vigilance time into feeding time. Dominant Great Tits seek the
presence of subordinate Parus species to
enhance foraging efficiency under safer conditions (using other species as
early warners), the converse being true for
subordinate species (i.e., they should avoid dominant Great Tits and
terminate heterospecific social foraging more often).
Vigilance
time of solitary Great Tits, Nuthatches, and three other Parus
species was not negatively correlated with interspecific
dominance status. In these small passerines, vigilance does not seem to be
directed towards the detection of a competitor species. Surveillance for
predators and detection of competitor species may be synchronous, nonexclusive
tasks. Scanning rate (number of scans per minute of feeding) was the same for
Great Tits that fed either solitarily or in pairs, but mean scan duration was
significantly shorter for individuals in groups than when solitary. Individual
Great Tits benefited from the presence of Coal, Blue, and Crested tits
(subordinate Parus species), by a lengthening
of the time spent at feeding patches and by a conversion of vigilance time into
feeding time.
CARRASCAL, L.M.; LÓPEZ, P.; MARTÍN, J.; SALVADOR, A. 1992. Basking
and antipredator behaviour in a high altitude lizard:
implications of heat-exchange rate. Ethology
92:143-154.
This
paper presents an observational and experimental study of the basking behaviour
and heat exchange rate of the montane lizard Lacerta monticola. The
results obtained by these procedures were coupled in order to understand
behavioural mechanisms promoting effective thermoregulation at high altitudes.
Heating rate was higher when body size was smaller, and substrate temperature
and sunrays incidence angle were higher. The lizards cooled faster when body
size and substrate temperature were lower, and when the body temperature of the
lizard going into shadow was higher. Time exposed to sun and mean duration of
basking periods were longer early in the morning, while bask frequency
increased through the morning. Our results suggest that time devoted to basking
is mainly obtained by regulating bask duration. Lizards obtained the necessary
time for heating by means of long basking periods. Mean travel distance per
minute and distance to the nearest refuge increased from early morning to
midday. These behavioural variables were tightly correlated with the expected
heating rate of individuals. Body size affects thermoregulatory behaviour as
well as locomotor activity. Juvenile lizards, with
small body mass and high surface-to-volume ratios, were subjected to faster
heating and cooling rates, basked more frequently than adults (but during
shorter periods), and devoted more time to locomotion than adults. The
thermoregulatory behaviour of L. monticola is
the result of the combination of shuttling heliothermy
by basking and the exploitation of thermal opportunities offered by patches in
shade through thermal exchange with the substrate.