Jaguar (Panthera onca) density and tenure in a critical biological corridor.

We estimated jaguar density and tenure, and investigated ranging behavior, using camera traps across the Maya Forest Corridor, a human-influenced landscape in central Belize that forms the only remaining connection for jaguar populations inhabiting two regional forest blocks: the Selva Maya and the Maya Mountain Massif. Jaguars were ubiquitous across the study area. Similar to the neighboring Selva Maya, mean density ranged from 1.5 to 3.1 jaguars per 100 km2, estimated by spatial capture-recapture models. Cameras detected almost twice as many males as females, probably reflecting detection bias, and males ranged more widely than females within the camera grid. Both sexes crossed two major rivers, while highway crossings were rare and male-biased, raising concern that the highway could prevent female movement if traffic increases. Jaguars were more transient where the landscape was fragmented with settlements and agriculture than in contiguous forest. Compared with jaguars in the protected forests of the Maya Mountains, jaguars in central Belize displayed a lower potential for investment in intraspecific communication, indicative of a lower quality landscape; however, we did detect mating behavior and juveniles. Tenure of individuals was shorter than in the protected forests, with a higher turnover rate for males than females. At least three-quarters of reported jaguar deaths caused by people were male jaguars, and the majority was retaliation for livestock predation. Jaguars seem relatively tolerant to the human-influenced landscape of central Belize. However, intensification of game hunting and lethal control of predators would threaten population persistence, while increased highway traffic and clear-cutting riparian forest would severely limit the corridor function. Our results show that the viability of the corridor, and thus the long-term survival of jaguar populations in this region, will depend on appropriate land-use planning, nonlethal control of livestock predators, enforcement of game hunting regulations, and wildlife-friendly features in future road developments.

Utilizando trampas-cámara, se estimó la densidad, permanencia y desplazamiento de jaguares a través del Corredor del Bosque Maya, un paisaje dominado por humanos en la zona central de Belice y que actualmente representa la única posibilidad de conectividad para las poblaciones de jaguares que habitan en dos grandes bloques boscosos regionales: La Selva Maya y El Macizo de las Montañas Mayas. Los jaguares estuvieron presentes en toda el área de estudio. De igual forma que en la vecina Selva Maya, la densidad media varió de 1.5 a 3.1 jaguares por cada 100 km2, estimada con modelos espaciales de captura-recaptura. Las cámaras detectaron casi el doble de machos que hembras, probablemente reflejando un sesgo de detección; y los machos se desplazaron más ampliamente que las hembras a lo largo de la cuadrícula de las cámaras. Jaguares de ambos sexos cruzaron dos ríos principales, mientras que el cruce de carreteras no fue común y estuvo sesgado hacia los machos, generando la preocupación de que las carreteras puedan impedir el movimiento de hembras si el tráfico vehicular aumenta. Los jaguares fueron más transitorios en paisajes fragmentados por asentamientos humanos y agricultura que en áreas de bosque continuo. Comparando con los jaguares de los bosques protegidos de las Montañas Mayas, los jaguares de la zona central de Belice mostraron menor potencial para invertir en comunicación intraespecífica, indicador de un paisaje de menor calidad; sin embargo, se detectó comportamiento de apareamientos y la presencia de juveniles. La permanencia de individuos fue más corta que en los bosques protegidos, con una tasa de recambio más alta para machos que para hembras. Al menos las tres cuartas partes de las muertes reportadas de jaguares causadas por humanos correspondieron a jaguares machos, la mayoría como retaliación por la muerte de ganado. Los jaguares parecen relativamente tolerantes del paisaje dominado por humanos en la zona central de Belice. Sin embargo, el aumento de la cacería de especies presa y el control letal de predadores amenazaría la persistencia de la población, mientras que el aumento del tráfico vehicular y la deforestación de bosques de galería reducirían severamente la funcionalidad del corredor. Nuestros resultados muestran que la viabilidad del corredor y por lo tanto la sobrevivencia de jaguares a largo plazo en esta región dependerá de la planificación apropiada del uso del suelo, de un control no letal de predadores de ganado, una mejor regulación de la cacería, y de una infraestructura amigable con la vida silvestre en las futuras carreteras.

Outcomes of reciprocal invasions between genetically diverse and genetically uniform populations of Daphnia obtusa (Kurz).

Ecological theory predicts that genetic variation produced by sexual reproduction results in niche diversification and provides a competitive advantage both to facilitate invasion into genetically uniform asexual populations and to withstand invasion by asexual competitors. We tested the hypothesis that a large group of diverse clones of Daphnia obtusa has greater competitive advantage when invading into genetically uniform populations of this species than a smaller group with inherently less genetic diversity. We compared competitive outcomes to those of genetically uniform groups of small and large size invading into genetically diverse populations. Genetically diverse invaders of initially large group size increased their representation by more than those of initially small size; in contrast, genetically uniform invaders of initially large group size diminished on average by more than those of initially small size. These results demonstrate an advantage to the genetic variation produced by sexual reproduction, both in invasion and resisting invasion, which we attribute to competitive release experienced by individuals in genetically diverse populations.

The accumulation of deleterious mutations within the frozen niche variation hypothesis.

The frozen niche variation hypothesis proposes that asexual clones exploit a fraction of a total resource niche available to the sexual population from which they arise. Differences in niche breadth may allow a period of coexistence between a sexual population and the faster reproducing asexual clones. Here, we model the longer term threat to the persistence of the sexual population from an accumulation of clonal diversity, balanced by the cost to the asexual population resulting from a faster rate of accumulation of deleterious mutations. We use Monte-Carlo simulations to quantify the interaction of niche breadth with accumulating deleterious mutations. These two mechanisms may act synergistically to prevent the extinction of the sexual population, given: (1) sufficient genetic variation, and consequently niche breadth, in the sexual population; (2) a relatively slow rate of accumulation of genetic diversity in the clonal population; (3) synergistic epistasis in the accumulation of deleterious mutations.

The ecological cost of sex.

Why sex prevails in nature remains one of the great puzzles of evolution. Sexual reproduction has an immediate cost relative to asexual reproduction, as males only express their contribution to population growth through females. With no males to sustain, an asexual mutant can double its relative representation in the population in successive generations. This is the widely accepted 'twofold cost of males'. Many studies have attempted to explain how sex can recoup this cost from fitness benefits associated with the recombination of parental genotypes, but these require complex biological environments that cycle over evolutionary timescales. In contrast, we have considered the ecological dynamics that govern asexual invasion. Here we show the existence of a threshold growth rate for the sexual population, above which the invasion is halted by intraspecific competition. The asexual population then exerts a weaker inhibitory effect on the carrying capacity of the sexual population than on its own carrying capacity. The stable outcome of this is coexistence on a depleted resource base. Under these ecological circumstances, longer-term benefits of sex may eventually drive out the asexual competitor.

Balanced dispersal between spatially varying local populations: an alternative to the source-sink model.

Analysis of long-term monitoring data on breeding collared flycatchers (Ficedula albicollis Temm.) has revealed equal numbers of immigrations and emigrations between neighboring populations of different sizes. Dispersal patterns were close to patterns simulated under a conditional dispersal and with populations near saturation level. Local growth rates of the 11 sites were computed and did not support the idea that the observed balanced exchanges could be the result of a source-sink system. This is the first empirical evidence for a system of discrete habitat patches with component populations that exist as simultaneous sources and sinks to their neighbors. Dispersal propensities were inversely related to population sizes, which showed little variation in time. These results are consistent with recent modeling of dispersal as an evolutionarily stable strategy, and they demonstrate that dispersal can be an active phenomenon requiring neither the dominance hierarchies nor the temporal instability generally invoked by ecological and population genetic models. We note a parallel to the concept of Ideal Free Distributions and discuss implications for the evolution of dispersal mechanisms in fragmented populations.

Physiological response of the European hedgehog to predator and nonpredator odour.

A respiratory chamber was used to investigate physiological responses of hedgehogs to predator and nonpredator odour cues, introduced by passing air through different faecal suspensions. Five recently caught hedgehogs showed a significant increase in oxygen consumption (29% +/- 18% at 95% c.i.) when treated with badger (predator) faecal suspension, and 10 hedgehogs held in captivity for ca. 2 years showed no significant response. The responses of recently caught hedgehogs to odour from badger (predator) and roe deer (non-predator) faecal suspensions were then investigated, over a range of concentrations spanning 3 orders of magnitude. Five hedgehogs were tested with badger odour; of these, 3 were also tested with roe deer odour. The mean rise in oxygen consumption was significantly greater in response to badger than to roe deer faecal suspension, but there was no significant variation in strength of response over the range of concentrations tested, and increased oxygen consumption was not associated with any increase in levels of visible activity. The responses are interpreted as an increase in arousal in response to a potential predatory threat. Lack of response in the captive-held animals raises questions about the welfare of such animals following release. Energy costs and foraging inefficiency associated with arousal may be significant factors of foraging decisions involving predation risk, but more naturalistic measurements would be required for any quantitative analysis.

Testing the role of intraguild predation in regulating hedgehog populations.

Potential competitors that eat each other can engender patterns of spatial segregation similar to those produced by competition, and distinguishable only by field manipulation. This paper reports the results of a perturbation experiment to test the factors responsible for small-scale discontinuities in the distribution of a common insectivore. Populations of hedgehogs (Erinaceus europaeus) were monitored following their introductions into an area where they had been absent, and into a neighbouring area where they were known to persist. The two sites had a similar availability of preferred habitat, and the growth rates of introduced hedgehogs were similar. The density of badgers (Meles meles), larger members of the same guild, appears to produce differences in mortality and dispersal, which returned the populations close to their original levels within 2 months of the transplant.

Temperature regulation of young coypus (Myocastor coypus) in air and water.

Coypus (Myocastor coypus Molina) have recently colonized temperate regions of Europe in large numbers, originating from populations indigenous to subtropical regions of South America. Observations of coypu behavior in the wild and in enclosures under a temperate climate showed a preference for close proximity to water and frequent swimming bouts. Little change was observed in the semiaquatic habit in winter, despite high mortality during this period, particularly among young and adult male coypus. Evidence for constraints on thermal adaptation was sought from measurements in a thermostatic chamber of the resting metabolic rate (RMR) of young coypus caught from wild populations in France and of the body (Tb) and skin (Tsk) temperatures as a function of ambient temperature (Ta). A light heterothermic response with deep Tb falling by 0.8 degree C and stabilizing at a new level of 36.7 degrees C was observed in water and air at Ta below the lower critical temperatures. In common with other semiaquatic mammals, RMR (2.94 W/kg) was high relative to terrestrial mammals of equivalent body mass. Minimal thermal conductance was 0.10 W.kg-1.degree C-1 in air for Ta between -10 and +20 degrees C, and conductance varied in water from 0.24 to 1.18 W.kg-1.degrees C-1 for Ta between 5 and 35 degrees C. The physiological adaptations to cold and particularly the high insulative value of the fur (80-90% of the insulation) help to explain the successful extension of the coypu's range to temperate regions. Energetic costs were nevertheless high in cold water, suggesting that social factors may be implicated in severe winter mortality, particularly dominance hierarchy regulating the persistent use of water bodies even under freezing conditions.