I study ecology and evolution of amphibian communities in mediterranean freshwater aquatic systems. To date I have worked on larval anurans. I am particularly interested in how animals resolve the trade-offs they are faced with and the role of phenotypic plasticity and population structure. I consider this at both ecological and evolutionary scales, combining field studies with laboratory experiments. To address this general problem, I measure traits important to the animal's performance (and ultimately, fitness) in its habitat and consider these trait values in the context of present-day habitat type and evolutionary history.
I developed my thesis research at the University of Barcelona (Spain) with Dr. Gustavo Llorente as tutor. The thesis research concerned evolutionary ecology and community ecology of amphibians in two different areas of a Mediterranean region. The goal of the research was to test how anuran species coexist along a lentic freshwater gradient from ephemeral to permanent ponds. The community structure across the gradient has been explained by different ecological models, based on different trade-offs and inherent properties of the species. To test the different models he used four-year field surveys of communities to characterise pond-breeding habitats (with respect to temporariness, predator abundance and competitor abundance) and to evaluate the dynamics and spatial structures of the metacommunity. He also designed lab experiments to quantify species traits and phenotypic plasticity (life-history, morphological and behavioural traits) in response to different circumstances found in nature: pond drying, presence of invertebrate predators and intra- and interspecific competition. Comparative analysis of phenotypic plasticity traits was made in relation to species ecological breadths (quantified from field surveys) and phylogenetic relationships. In general, species that use a wide variety of habitats or unpredictable environments showed a greater plasticity of responses than those occurring in predictable habitats. At the two extremes of the hydroperiod (ephemeral and permanent ponds) there were specialists with limited plasticity, whereas species from intermediate temporary ponds showed higher levels of plasticity. Results therefore supported the hypothesis that interspecific differences in plasticity are adaptive and are related to ecological breadth and unpredictability of habitat. The correlations among traits of the different species reflected trade-offs suggested by the models (colonisation-competition; predator-permanence gradient; and competition ability-permanence gradient), but correlation coefficients did not favour any single trade-off model over the others. These results suggest that the community studied can be interpreted as a metacommunity in which local interactions and regional processes (colonisation-extinction rates) are related, and they emphasise the importance of habitat heterogeneity for both: local and regional diversity maintenance.
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One of the great challenges for the 21st century is to develop and implement strategies to avoid loosing a large amount of biodiversity. This becomes crucial by taking into account the high current rates of human population growth and energy use, the increasing demand for area and, consequently, the high rates of habitat loss, fragmentation and species extinctions. Contemporary populations are increasingly threatened by these human-induced environmental changes, because modify habitats and often cause strong selection at very short time-scales. In the past few decades, studies by evolutionary biologists have revealed that selection in natural populations can be strong, and can cause evolutionary shifts within a few generations. The majority of rapid evolutionary changes reported in natural populations involve response to anthropogenic pressures, but many local populations fail to adapt to such changes and suffer extinctions. The recognition of these fast evolutionary processes within a few generations has stimulated an awareness that evolutionary concepts need to be incorporated in conservation thinking, which can have important consequences for species conservation, management and restoration.
Genetic variation provides the heritable resource that serves as the basis for evolutionary change, and loss of genetic diversity may, over time, negatively impact a population’s viability and the potential for further adaptive change in response to new selective challenges. However, most conservation geneticists only use molecular marker traits, and many discussions of genetics in conservation biology have centered on the topic of heterozygosity or related measures of the within-population component of genetic variation, yet these may not reflect the adaptive potential of populations. Causal links between genetic variation in populations and fitness have proved difficult to establish, and molecular markers usually do not reflect patterns of selection. As a result, neutral molecular markers cannot be used to infer scales of adaptation or patterns of variation in traits that might be important in adapting to a changing environment. Therefore other populations traits more clearly related to fitness must be measured to estimate diversity and develop management programs to preserve ecotypes and evolutionary mechanisms. Quantitative genetic techniques have not yet received much attention in the conservation field, but are likely to reveal the variation that is most closely associated with components of fitness. Measures of quantitative genetic variation do better reflect variation in fitness traits, but the distribution of quantitative genetic variation in natural environments is poorly understood, especially in species that live in metapopulations.
In this context, it is now recognized that knowledge of population genetic structure and genetic diversity distribution are important to evaluate population viability and establish significant units for conservation. Perhaps more importantly, patterns of genetic structure within and among populations should be integrated into a more complex evaluation of human occupation patterns, so that genetic parameters can be explicitly analyzed on a human occupied landscape. This also leads to an evaluation of how human modifications at landscape level affect genetic diversity. Both possibilities can be integrated into a single framework, which has been recently called “landscape genetics”, analogous to the well-established field of landscape ecology, but for the moment this integration only incorporates molecular genetic data with landscape information without including quantitative genetic data of phenotypic fitness related traits. Population, quantitative and landscape genetics have developed rapidly in recent years but there is a need now to integrate these fields for practical applications in ecology and conservation biology.
Amphibians have been widely used as indicators of habitat change, because they are quite sensitive to human induced habitat changes. At the same time, there is a general need to understand these effects, because amphibian population declines have been reported worldwide. Studies in amphibian population genetics revealing a high level of population structure, which can be associated with their ecological and behavioral characteristics, especially the relatively low dispersion rates, high habitat fidelity and specificity. The effects of habitat loss and fragmentation cannot be understood at local spatial scales, and analyses at broader geographical extents (at least regional or landscape levels) are necessary to evaluate how complex processes related to human occupation interact at these scales and affect biodiversity.
Many studies in conservation genetics have been focused on endangered species, hoping that a better understanding of genetic parameters furnishes effective information to increase their persistence. On the other hand, species locally abundant or widely distributed can be informative on how broad scale processes of habitat loss and fragmentation affected population genetic structure. These approaches are of course not mutually exclusive, but this partition may be useful to ensure how non-endangered, highly abundant and widely distributed species are also important targets for applied genetic analyses. We will investigate how landscape structure affects the distribution of quantitative and molecular genetic variation of the widely distributed frog Rana arvalis in Uppland (Sweden). To do that we will combine molecular genetics analyses with quantitative genetic experiments and landscape studies to increase our understanding of genetic diversity distribution.
Abstract: Predicting the biodiversity impacts of global warming implies we know where and with
what magnitude these impacts will be encountered. Amphibians are currently the most
threatened vertebrates, mainly due to habitat loss and to emerging infectious diseases.
Global warming may further exacerbate their decline in the near future, although the
impact might vary geographically. We predicted that subtropical amphibians should be
relatively susceptible to warming induced extinctions because their upper critical
thermal limits (CTmax) might be only slightly higher than maximum pond temperatures
(Tmax). We tested this prediction by measuring CTmax and Tmax for 47 larval amphibian
species from two thermally distinct subtropical communities (the warm community of
the Gran Chaco and the cool community of Atlantic Forest, northern Argentina), as well
as from one European temperate community. Upper thermal tolerances of tadpoles were
positively correlated (controlling for phylogeny) with maximum pond temperatures,
although the slope was steeper in subtropical than in temperate species. CTmax values
were lowest in temperate species and highest in the subtropical warm community,
which paradoxically, had very low warming tolerance (CTmax â Tmax) and therefore may
be prone to future local extinction from acute thermal stress if rising pond Tmax soon
exceeds their CTmax. Canopy protected subtropical cool species have larger warming
tolerance and thus should be less impacted by peak temperatures. Temperate species are
relatively secure to warming impacts, except for late breeders with low thermal
tolerance which may be exposed to physiological thermal stress in the coming years.
Abstract: Mediterranean temporary ponds (MTPs) are crucial breeding sites for local amphibians, a faunal group in decline in the Mediterranean mainly due to wetland destruction. Although the disappearance of lentic habitats in other regions of the world has been ameliorated by the creation and restoration of wetlands, these tactics remain untested in Mediterranean wetlands. To evaluate the amphibian colonization dynamics of artificial MTPs in the north-eastern Iberian Peninsula, we monitored two artificial MTPs (one in a high-diversity area and the other in a low-diversity area) over 2 years. We selected reference wetlands at each area, and amphibian communities of man-made MTPs were compared to those of reference wetlands. We found that, beginning in the first year, artificial MTPs were a valuable habitat for regional amphibian fauna. Posteriorly, we focused on the reproductive success of the natterjack toad, Bufo calamita. Using a drift fence equipped with pit-fall traps, we measured the abundance of both reproductive adults entering the pond and post-metamorphic individuals exiting the pond. Using mark-recapture methods, we analyzed the time and energy costs associated with reproduction in the artificial MTPs. We observed a highly variable colonization dynamics between sites, between hydroperiods, and within hydroperiods, and these dynamics often depended on meteorological factors. Our results suggest that even at a short timescale, native amphibian species such as B. calamita can benefit from wetland creation in the Mediterranean region.
Abstract: Anurans breed in a variety of aquatic habitats with contrasting levels of desiccation risk, which may result in selection for faster development during larval stages. Previous studies suggest that species in ephemeral ponds reduce their developmental times to minimize desiccation risks, although it is not clear how variation in desiccation risk affects developmental strategies in different species. Employing a comparative phylogenetic approach including data from published and unpublished studies encompassing 62 observations across 30 species, we tested if species breeding in ephemeral ponds (High risk) develop faster than those from permanent ponds (Low risk) and/or show increased developmental plasticity in response to drying conditions. Our analyses support shorter developmental times in High risk, primarily by decreasing body mass at metamorphosis. Plasticity in developmental times was small and did not differ between groups. However, accelerated development in High risk species generally resulted in reduced sizes at metamorphosis, while some Low risk species were able compensate this effect by increasing mean growth rates. Taken together, our results suggest that plastic responses in species breeding in ephemeral ponds are constrained by a general trade-off between development and growth rates.
Abstract: One of the main questions in evolutionary and conservation biology is how geographical and environmental features of the landscape shape neutral and adaptive genetic variation in natural populations. The identification of genomic polymorphisms that account for adaptive variation can aid in finding candidate loci for local adaptation. Consequently, a comparison of spatial patterns in neutral markers and loci under selection may allow help to disentangle the effects of gene flow, genetic drift and selection at the landscape scale. Many amphibians breed in wetlands, which differ in environmental conditions and in the degree of isolation, enhancing the potential for local adaptation. We used microsatellite markers to measure genetic differentiation among 17 local populations of Rana arvalis breeding in a network of wetlands. We found that locus RC08604 deviated from neutral expectations, suggesting that it is a good candidate for directional selection. We used a genetic network analysis to show that the allele distribution in this locus is correlated with habitat characteristics, whereas this was not the case at neutral markers which displayed a different allele distribution and population network in the study area. The graph approach illustrated the genomic heterogeneity (neutral loci vs. the candidate locus for directional selection) of gene exchange and genetic divergence among populations under directional selection. Limited gene flow between wetlands was only observed at the candidate genomic region under directional selection. RC08604 is partially located inside an up-regulated thyroid-hormone receptor (TRβ) gene coordinating the expression of other genes during metamorphosis, and appears to be linked with variation in larval life-history traits found among R. arvalis populations. We suggest that directional selection on genes coding larval life-history traits is strong enough to maintain the divergence in these genomic regions, reducing the effective recombination of locally adapted alleles but not in other regions of the genome. Integrating this knowledge into conservation plans at the landscape scale will improve the design of management strategies to preserve adaptive genetic diversity in wetland networks.
Abstract: In organisms with complex life cycles, environmentally induced plasticity across sequen- tial stages can have important consequences on morphology and life history traits such as develop- mental and growth rates. However, previous research in amphibians and other ectothermic verte- brates suggests that some morphological traits are generally insensitive to environmental inductions. We conducted a literature survey to examine the allometric responses in relative hind leg length and head shape of post-metamorphic anuran amphibians to induced environmental (temperature, re- source level, predation and desiccation risk) variation operating during the larval phase in 44 studies using 19 species. To estimate and compare plastic responses across studies, we employed both an in- dex of plasticity and effect sizes from a meta-analysis. We found contrasting trait responses to different environmental cues. Higher temperatures increased development more than growth rate and induced smaller heads but not overall shifts in hind leg length. In contrast, an increment in resource availabil- ity increased growth more than development, with a parallel increase in hind leg length but no change in head shape. Increases in predation risk decreased both development and growth rates and slightly reduced relative hind leg length, but there was no change in head shape. Pond desiccation induced quick development and low growth rates, with no changes in morphology. Across environments, both hind leg and head shape plasticity were positively correlated with growth rate plasticity. However, plasticity of developmental rate was only correlated with head shape plasticity. Overall, these results suggest that environmental trends predicted by global warming projections, such as increasing pond temperature and accelerating pond desiccation, will significantly influence hind leg and head morphology in metamorphic frogs, which may affect performance and, ultimately, fitness.
Abstract: In ectotherms, variation in life history traits among populations is common and suggests local adaptation. However, geographic variation itself is not a proof for local adaptation, as genetic drift and gene flow may also shape patterns of quantitative variation. We studied local and regional variation in means and phenotypic plasticity of larval life history traits in the common frog Rana temporaria using six populations from central Sweden, breeding in either open-canopy or partially closed-canopy ponds. To separate local adaptation from genetic drift, we compared differentiation in quantitative genetic traits (QST) obtained from a common garden experiment with differentiation in presumably neutral microsatellite markers (FST). We found that R. temporaria populations differ in means and plasticities of life history traits in different temperatures at local, and in FST at regional scale. Comparisons of differentiation in quantitative traits and in molecular markers suggested that natural selection was responsible for the divergence in growth and development rates as well as in temperature-induced plasticity, indicating local adaptation. However, at low temperature, the role of genetic drift could not be separated from selection. Phenotypes were correlated with forest canopy closure, but not with geographical or genetic distance. These results indicate that local adaptation can evolve in the presence of ongoing gene flow among the populations, and that natural selection is strong in this system.
Abstract: The longitudinal movements and abiotic factors that determine the distribution of Pyrenean mountain newts (males, females, amplexus and metamorphic newts) were examined in a 1500 meters segment of a Pre-Pyrenean stream. Migration of adult newts was studied by means of capture-recapture techniques in the course of one year. Our results indicate that the mean distance the newts migrated per year was less than 50 meters and the population could be considered sedentary. No significant differences in longitudinal movement patterns between the sexes or throughout time were observed. Habitat variables determining newt abundance was estimated by means GLM analysis. Our results further indicate that the number of refugia (wood debris, stones and fissures) determines the distribution of newts. Larval abundance was correlated with stream-bed structure.
Abstract: Literature suggests that coexistence of amphibian species at a regional scale could be determined by spatial and temporal segregation of breeding habitats. We tested these assumptions in a Mediterranean littoral region of the NE of the Iberian Peninsula. During 5 years we measured reproductive effort of species, tadpole abundance and their potential predators in isolated ponds. Species distributed along a hydroperiod gradient of water temporality, which ranges from ephemeral pools to permanent waters. Results showing a clear preference of some species along the gradient, but with an imperfect segregation among habitats, and many species use different kinds of habitats in function of their temporality. The number and abundance of large predators increased along the gradient, showing greater values in permanent ponds. Also we detected a temporal segregation of reproductive events. Many species showed a great plasticity of reproduction with two peaks: one in spring and the other in autumn. In spite of this temporal segregation, a large overlap during larval phase was observed among species.
Abstract: The expansion of Discoglossus pictus in Catalonia is analyzed at the same time as a model of potential distribution of the species is developed. From its introduction in Banyuls-sur-Mer about 100 years ago, Discoglossus pictus has been dispersed about 140 km towards the South and about 60 km towards the interior. A global dispersion rate of 1,53 km/year ± 0,8 km has been estimated. Nowadays, the distribution of Discoglossus pictus takes up an approximate surface of 4200 km2 in Spain. Although Discoglossus pictus can coincide in ponds with all the present species in Catalonia, it prefers to use temporary or ephemeral environments for the reproduction, as Rana temporaria, Bufo calamita and Pelodytes punctatus. The analysis of the trophic, habitat and distribution overlap shows that the species that it can interact with Discoglossus pictus in the adult phase are Bufo calamita, Bufo bufo, Pelophylax perezi and Hyla meridionalis. The results indicate a certain degree of interference in adult level, especially with Bufo calamita, although it is necessary to clarify if this takes place also in the larval phase.
Abstract: The introduction of invasive species is, after habitat destruction,
the second most important cause of biodiversity loss on the
planet (Devine 1998; IUCN 2000; Mack et al. 2000). The main
problems related to the introduction of invasive species are competition
with local fauna, introduction of pathogens and genetic
pollution of autochthonous populations (Elton 1958; Dodd and
Seigel 1991; Butterfield et al. 1997; Arano et al. 1995; Manchester
and Bullock 2000). According to one estimate, 39% of all known
extinctions that have taken place in the last 300 years have been as
a result of the introduction of exotic species (Guijarro, 2001).
Abstract: Ecological conditions and food quality have influence on age and size at
metamorphosis of organisms with complex life cycles. However, little is known
about the foraging behaviour and how diet choice is influenced by the ecological
conditions.
The present study poses two major questions: (1) how do different diets (high
protein, low protein and both diets together) influence larval performance, and (2)
how does diet choice change with ecological conditions (interference competition,
predation and pond drying)? To address the second question, we offered both types
of food to tadpoles under the different circumstances. We measured food
consumption of the two food types, along with the growth rate and developmental
stage of tadpoles. We expected that under unfavourable growth conditions, larvae
would select high-protein food, which would promote development and allow
individuals to escape these high-risk environments.
High-protein food promotes development, but results in smaller tadpoles, whereas
low-protein food promotes growth with slower development. The mixture of the two
is better only in terms of growth rate. Our study of tadpoles showed that diet
selection may not be constant but can vary depending on the ecological context in
predictable ways. When exposed to interference competition and drying ponds,
tadpoles fed on food that enhanced development, whereas in the control group and
in predation treatments, they fed selectively on food that favoured growth. Our data
indicate that diet selection by tadpoles may confer adaptive responses to ecological
changes. Such selection/responses would increase growth, development, and
survival.
Abstract: The anuran larval guild is frequently characterised by the co-occurrence, with high niche overlap, of distinct species
in the same pond at variables densities during development. Anuran larvae have therefore been widely studied as a model
system for competition. Body size and activity level are considered the most important factors that influence the outcome of
competition between tadpoles. As species from temporary ponds normally show higher activity levels in order to achieve rapid
growth and thus reduce the risk of desiccation, these species are often considered superior competitors. We designed several
laboratory experiments to examine the intra- and interspecific effects on growth rate, mass at metamorphosis and survival to
metamorphosis of six species in a Mediterranean area. Body size and activity level were used as explanatory covariables to
determine competitive ability among species. An asymmetric and hierarchical relationship was found among the six species.
Larger tadpole species were more successful in competitive interactions than smaller ones, but no relationship was found
between activity level and competition effects. Species typically found in temporary ponds (Pelodytes punctatus and Bufo
calamita) were considered poor competitors in contrast with other communities studied. Species with low competitive ability
can persist by using refuges in which competition is reduced (e.g. ephemeral ponds).
Abstract: In a field survey the distribution of
pond-breeding anuran species and their potential
large predators was investigated along a freshwater
habitat gradient, ranging from ephemeral pools
to permanent ponds. In a laboratory experiment
predator-induced plasticity was examined for all
tadpole species to test whether the plastic
response of ephemeral and temporary pond species
differs from that of permanent pond species.
Desiccation and predation pose conflicting demands;
reduced activity lowers the risk of death by
predation but increases the risk of death by
desiccation. It was expected that species from
time-constrained habitats would display a morphotype
that would reduce vulnerability to invertebrate
predators, thus allowing these species to
maintain a high level of activity, whereas species
from permanent ponds would avoid predation
both morphologically and behaviourally. Species
distribution and predator composition along the
hydroperiod gradient differed. Variations between
ephemeral and temporary ponds can be
attributed to hydroperiod differences and the
presence of large invertebrate predators in temporary
ponds, whereas the contrasts between
temporary and permanent ponds can only be
attributed to the hydroperiod, since the presence
and abundance of top predators are similar in both
habitat types. With the exception of bufonids, all
species showed predator-induced plasticity in
agreement with previous studies. Tadpole species
differed in the integration of the phenotypic traits
measured, but differences observed between
species could not be attributed only to habitat.
Species from temporary habitats showed an
expected response, with a low reduction of activity
in comparison with the rest of the species. The lack
of general patterns in the morphological changes
suggests that species within the same habitat type
did not converge on similar phenotypes, perhaps
due to functional constraints on differences in
microhabitat use in the water column.
Abstract: 1.
The concept of metacommunity is based on the hypothesis that species occurrence
depends on species dynamics and interactions on local and regional scales via the
movements of individuals between localities. Metacommunity approaches are currently
being applied to pond breeding taxa such as amphibians.
2.
Given that animal movement is also influenced by the physical quality of the matrix
to be crossed to reach a breeding habitat and by the affinity of the species for specific
terrestrial habitats, matrix characteristics may enhance or hinder dispersal success.
These characteristics would, in turn, affect the composition of larval assemblages at
local level and, consequently, determine metacommunity structure and dynamics.
3.
Here we compared the structures and dynamics of two metacommunities with the
same pool of anurans along similar freshwater gradients in two regions that are well
differentiated in terms of their respective terrestrial matrix.
4.
Abundance of tadpole species and species assemblage in the two regions were
determined principally by local processes (at pond level); however, the structure and
dynamics of the communities differed. In one region species abundance was explained
in part by landscape factors and consequently showed lower co-occurrence and lower
colonization rates (species sorting models) indicating that terrestrial habitat could
restrict animal movements, whereas in the other region higher co-occurrence and higher
colonization rates (mass effect models) indicated low dispersal limitations.
Abstract: The Common Toad Bufo bufo is the amphibian with the highest rates of road mortality in
many European countries. This elevated incidence of road kills has frequently been associated with migration
to breeding sites. In this study, we analysed the mortality of the Common Toad in the road network in Catalonia
(NE Spain), and investigated the related causative factors on four roads near a breeding site in the Pyrenees.
Results suggest that the high mortality rate is due to a combination of factors: toad abundance, traffic density
and quality of water bodies for breeding. On the road with the highest incidence of road kills we investigated
whether deaths occurred at specific spots or in a random manner. The road was divided into 500 m sections
and each section was classified according to biotic (type of vegetation) and abiotic (presence of streams,
roadside topography) variables. Multiple correspondence analysis showed that sections with streams crossing
under the road had the highest mortality rate, suggesting that such water bodies flowing into the breeding pond
are the toadsâ main migratory pathways for hibernation and breeding. As toads use the same migratory routes
each year, it is critical to identify areas with a high potential mortality so that efficient measures can be
designed to increase wildlife permeability, and thereby reduce habitat fragmentation. This methodology could
be applied in other areas with high amphibian mortality.
Abstract: Question: In organisms with a complex life cycle, are stages phenotypically coupled or does
metamorphosis break all developmental links?
Hypothesis: For those organisms with developmental phenotypic plasticity, if metamorphosis
does not break all developmental links, then changes in juvenile performance will occur as a
cost of phenotypic plasticity.
Organism: The anuran Pelodytes punctatus from the north-east Iberian Peninsula.
Methods: Two experimental treatments: (1) constant water level and (2) drying treatment.
Larvae phenotypic plasticity was measured using morphological and life-history (time to
and mass at metamorphosis) traits. After metamorphosis, toadlet morphology and its jump
capacity were measured in both treatments.
Results: Tadpoles in the drying treatment accelerated metamorphosis and reached this stage
with a lower body mass. They also showed a reduced tail fin during the larval phase. Toadlets
in the drying treatment showed shorter and less muscular hind limbs and a reduced jump
capacity compared with individuals in the constant water treatment independently of time of
development.
Abstract: Question: Is developmental phenotypic plasticity an adaptive trait and therefore more flexible
in variable and unpredictable environments?
Organism: The anuran larvae community encompassing Alytes obstetricans, Pelodytes
punctatus, Bufo bufo, B. calamita, Hyla meridionalis, and Rana perezi.
Methods: In the field, we examined the ecological breadth (spatial and temporal variability)
of the six species along a pond permanency gradient in 240 ponds. In the laboratory, we
measured developmental plasticity (time to and size at metamorphosis) of each species using
two treatments: (1) constant water level and (2) drying treatment. A comparative analysis was
undertaken of developmental plasticity and the function of species ecological breadth and their
phylogenetic relationship.
Results: Species that use a wide variety of habitats or unpredictable environments showed a
greater plasticity of responses than those occurring in predictable habitats. At the two extremes
of the hydroperiod (ephemeral and permanent ponds), specialist developmental phenotypes
with limited plasticity occur, whereas species from variable habitats (temporary ponds) can be
considered plastic strategists with asymmetric bet-hedging. Our results support the hypothesis
that interspecific differences in developmental phenotypic plasticity are adaptive and are related
to ecological breadth and unpredictability.
Abstract: We studied the temporal breeding patterns and strategies of anuran assemblages in the Mediterranean region over
five consecutive years. We collected monthly data on the number of clutches, tadpoles and juveniles presence of six species
in 98 ponds. The data showed a great temporal segregation of species. Species using permanent ponds have a breeding peak
that is related to temperature whereas reproductive success in temporary pond breeders is determined by rainfall pulses. Many
species showed great plasticity of reproduction with two peaks: one in spring and the other in autumn. In spite of this temporal
segregation, a large overlap was observed among species during the larval phase period. Three species (Alytes obstetricans,
Pelodytes punctatus and Rana perezi) have over-wintering tadpoles. We discuss temporal segregation, differences between
species in their breeding strategies and variable conditions between years as factors that favour the temporal coexistence of
species in the Mediterranean region.
Abstract: Experimental manipulations of the densities of two larval anurans, Pelodytes punctatus
and Bufo bufo, showed that these species compete asymmetrically in semi-natural
conditions. Growth, mass at metamorphosis, date of metamorphosis, and survival were
used as measures of response to interspecific competition. A mechanistic approach was
used to collect information on the behaviour of the two species in different conditions.
The competitive superiority of Pelodytes at individual level was correlated with a larger
body, faster growth rate, increased per capita competitive impact on conspecifics, and
greater reduction in the availability of trophic and spatial resources. In the presence of
Pelodytes, Bufo showed slower growth, smaller size at metamorphosis and reduced
survival. In the interspecific treatments Bufo individuals modified their behaviour by
increasing activity and use of the water column while Pelodytes did not change their
foraging activity or space use in the aquaria. However, the presence of Bufo resulted in
a reduced larval period and smaller size at metamorphosis. We hypothesise that the
presence of Bufo act as a signal of environmental degradation and shorten the larval
period of Pelodytes, a typical temporal pond breeder. The smaller Bufo tadpoles are
potentially stronger competitors at population level because they use relatively large
amounts of energy (greater densities and higher metabolic rates). Consequently, they
use larger proportions of the shared resources than their larger competitor. A possible
evolutionary response for larger tadpoles is the development of interference
mechanisms or ââescapingââ from ephemeral ponds where mortality by drying
represent a high risk.
Abstract: To understand the interplay of local selection and gene flow it is necessary to examine adaptation over habitat mosaics with different types of patchy habitats in which variation in gene flow, selection, and drift can potentially produce varying evolutionary outcomes. We investigated the interplay of these factors over a 35x35 km fine-grained habitat mosaic with different temperature and predation environments in 18 populations of the anuran Rana arvalis. To test adaptive differentiation among populations, we compared quantitative genetic divergence in phenotypic traits measured under laboratory standard conditions (QST) and putatively neutral polymorphic microsatellites (FST) by contrasting QST and FST values. We detected evidence for directional selection for local optima in three of the quantitative traits we measured, QST being higher than FST (FST = 0.016) in growth rate (QST = 0.355), larval period (0.275) and gut length (0.576). Phenotypic traits were correlated with habitat characteristics suggesting a strong selection for similar phenotypes as a function of habitat. The low values of FST detected are in concordance with the very small amount of population structure detected inside the area of study, making definition of population boundaries difficult. The system showed characteristics of âsmall-worldâ networks which enhance gene-propagation speed. These results suggest that phenotypic divergence is governed by different mechanisms than divergence in neutral markers and arises at spatial scales that are independent from variation in neutral markers.
Abstract: We present the first approach to the genetic diversity and structure of the Balearic toad (Bufo balearicus Boettger, 1880) for the island of Menorca. Forty-one individ- uals from 21 localities were analyzed for ten microsatellite loci. We used geo-refer- enced individual multilocus genotypes and a model-based clustering method for the inference of the number of populations and of the spatial location of genetic dis- continuities between those populations.
Only six of the microsatellites analyzed were polymorphic. We revealed a northwest- ern area inhabited by a single population with several well-connected localities and another set of populations in the southeast that includes a few unconnected small units with genetically significant differences among them as well as with the individ- uals from the northwest of the island. The observed fragmentation may be explained by shifts from agricultural to tourism practices that have been taking place on the island of Menorca since the 1960s. The abandonment of rural activities in favor of urbanization and concomitant service areas has mostly affected the southeast of the island and is currently threatening the overall geographic connectivity between the different farming areas of the island that are inhabited by the Balearic toad.
Abstract: The thesis research concerned evolutionary ecology and community ecology of amphibians in two different areas of a Mediterranean region. The goal of the research was to test how anuran species coexist along a lentic freshwater gradient from ephemeral to permanent ponds. The community structure across the gradient has been explained by different ecological models, based on different trade-offs and inherent properties of the species. To test the different models he used four-year field surveys of communities to characterise pond-breeding habitats (with respect to temporariness, predator abundance and competitor abundance) and to evaluate the dynamics and spatial structures of the metacommunity. He also designed lab experiments to quantify species traits and phenotypic plasticity (life-history, morphological and behavioural traits) in response to different circumstances found in nature: pond drying, presence of invertebrate predators and intra- and interspecific competition. Comparative analysis of phenotypic plasticity traits was made in relation to species ecological breadths (quantified from field surveys) and phylogenetic relationships. In general, species that use a wide variety of habitats or unpredictable environments showed a greater plasticity of responses than those occurring in predictable habitats. At the two extremes of the hydroperiod (ephemeral and permanent ponds) there were specialists with limited plasticity, whereas species from intermediate temporary ponds showed higher levels of plasticity. Results therefore supported the hypothesis that interspecific differences in plasticity are adaptive and are related to ecological breadth and unpredictability of habitat. The correlations among traits of the different species reflected trade-offs suggested by the models (colonisation-competition; predator-permanence gradient; and competition ability-permanence gradient), but correlation coefficients did not favour any single trade-off model over the others. These results suggest that the community studied can be interpreted as a metacommunity in which local interactions and regional processes (colonisation-extinction rates) are related, and they emphasise the importance of habitat heterogeneity for both: local and regional diversity maintenance.
