Turtle mating patterns buffer against disruptive effects of climate change

For organisms with temperature-dependent sex determination (TSD), skewed offspring sex ratios are common. However, climate warming poses the unique threat of producing extreme sex ratio biases that could ultimately lead to population extinctions. In marine turtles, highly female-skewed hatchling sex ratios already occur and predicted increases in global temperatures are expected to exacerbate this trend, unless species can adapt. However, it is not known whether offspring sex ratios persist into adulthood, or whether variation in male mating success intensifies the impact of a shortage of males on effective population size. Here, we use parentage analysis to show that in a rookery of the endangered green turtle (Chelonia mydas), despite an offspring sex ratio of 95 per cent females, there were at least 1.4 reproductive males to every breeding female. Our results suggest that male reproductive intervals may be shorter than the 2-4 years typical for females, and/or that males move between aggregations of receptive females, an inference supported by our satellite tracking, which shows that male turtles may visit multiple rookeries. We suggest that male mating patterns have the potential to buffer the disruptive effects of climate change on marine turtle populations, many of which are already seriously threatened.     

Survival rates in a small hibernator,the edible dormouse: a comparison across Europe

Understanding how local environmental factors lead to temporal variability of vital rates and to plasticity of life history tactics is one of the central questions in population ecology. We used long‐term capture‐recapture data from five populations of a small hibernating rodent, the edible dormouse Glis glis, collected over a large geographical range across Europe, to determine and analyze both seasonal patterns of local survival and their relation to reproductive activity. In all populations studied, survival was lowest in early summer, higher in late summer and highest during hibernation in winter. In reproductive years survival was always lower than in non‐reproductive years, and females had higher survival rates than males. Very high survival rates during winter indicate that edible dormice rarely die from starvation due to insufficient energy reserves during the hibernation period. Increased mortality in early summer was most likely caused by high predation risk and unmet energy demands. Those effects have probably an even stronger impact in reproductive years, in which dormice were more active. Although these patterns could be found in all areas, there were also considerable differences in average survival rates, with resulting differences in mean lifetime reproductive success between populations. Our results suggest that edible dormice have adapted their life history strategies to maximize lifetime reproductive success depending on the area specific frequency of seeding events of trees producing energy‐rich seeds.     

Climate influences on female survival in a declining population of southern elephant seals (Mirounga leonina)

The Southern Ocean has been disproportionately affected by climate change and is therefore an ideal place to study the influence of changing environmental conditions on ecosystems. Changes in the demography of predator populations are indicators of broader shifts in food web structure, but long‐term data are required to study these effects. Southern elephant seals (Mirounga leonina) from Macquarie Island have consistently decreased in population size while all other major populations across the Southern Ocean have recently stabilized or are increasing. Two long‐term mark‐recapture studies (1956–1967 and 1993–2009) have monitored this population, which provides an opportunity to investigate demographic performance over a range of climatic conditions. Using a 9‐state matrix population model, we estimated climate influences on female survival by incorporating two major climatic indices into our model: The Southern Annular Mode (SAM) and the Southern Oscillation Index (SOI). Our best model included a 1 year lagged effect of SAM and an unlagged SOI as covariates. A positive relationship with SAM1 (lagged) related the previous year''s SAM with juvenile survival, potentially due to changes in local prey availability surrounding Macquarie Island. The unlagged SOI had a negative effect on both juvenile and adult seals, indicating that sea ice dynamics and access to foraging grounds on the East Antarctic continental shelf could explain the different contributions of ENSO events on the survival of females in this population.     

Nonlinear impact of climate on survival in a migratory white stork population

1. There is growing evidence that ongoing climate change affects populations and species. Physiological limitation and phenotypic plasticity suggest nonlinear response of vital rates to climatic parameters, the intensity of environmental impact might be more pronounced while the frequency of extreme events increases. However, a poor understanding of these patterns presently hampers our predictive capabilities. 2. A recent climatic shift in the Sahel, from droughty to less severe condition, offers a good opportunity to test for an influence of the climatic regime on the response of organisms to their environment. Using a long-term capture-mark-recapture data set on a white stork (Ciconia ciconia) population wintering in Sahel, we investigated potential change in the impact of environmental conditions on survival and recruitment probabilities between 1981 and 2003. 3. We observed a decrease in the strength of the link between survival and Sahel rainfall during the last decade, down to a nondetectable level. Whether Sahel climate was found to affect the survival of storks under droughty conditions, individuals did not seem to respond to climatic variation when precipitation was more abundant. 4. This result gives evidence to a nonlinear response of a migrant bird to wintering environment. Present climate seems to fluctuate within a range of condition providing enough resources to maximize stork's survival. It suggests that whereas inter-annual variability impacted individuals, pluri-annual average condition affected the intensity of this impact. Such pattern may be more widespread than thought, and its modelling will be crucial to predict the impact of future climate change on population dynamics.     

Spatial variation in age-specific probabilities of first reproduction for Weddell seals

Spatial variation in vital rates can affect the dynamics and persistence of a population. We evaluated the prediction that age-specific probabilities of survival and first reproduction for Weddell seals would vary as a function of birth location in Erebus Bay, Antarctica. We used multi-state mark–resight models and 25 years of data to estimate demographic rates for female seals. We predicted that probabilities of survival and first reproduction would be higher for seals born at near-shore colonies or more southerly-located colonies with consistent ice conditions. Contrary to predictions, results revealed higher age-specific probabilities of first reproduction at offshore colonies relative to near-shore colonies and no spatial variation in survival rates. For 7-year old females (average age at 1st reproduction=7.6 years old) born at offshore colonies to mothers aged 10.8 years (average maternal age), probability of first reproduction was 0.43 (SE=0.07), whereas probability of first reproduction for females born at near-shore colonies was 0.30 (SE=0.05) based on estimates from our top-ranked model. Breeding probabilities following first reproduction were also higher at offshore colonies. Thus, our results (1) provide evidence of spatial variation in breeding probabilities, (2) reveal the importance of birth location on a female's vital rates, and (3) suggest that the effect persisted for many years. Birth-colony effects may be attributed to spatial variation in prey availability, or to heterogeneity in female quality in this population. If females who are superior competitors consistently chose offshore colonies for pupping, pups born at these locations may have inherited those superior qualities and displayed higher probabilities of first reproduction, relative to seals born at other colonies. Further research into physical or food-related differences among colonies may offer insight into spatial variation in breeding probabilities documented in this paper.     

Mark‐recapture modeling accounting for state uncertainty provides concurrent estimates of survival and fecundity in a protected harbor seal population

Harbor seal breeding behavior and habitats constrain opportunities for individual‐based studies, and no current estimates of both survival and fecundity exist for any of the populations studied worldwide. As a result, the drivers underlying the variable trends in abundance exhibited by harbor seal populations around the world remain uncertain. We developed an individual‐based study of harbor seals in northeast Scotland, whereby data were collected during daily photo‐identification surveys throughout the pupping seasons between 2006 and 2011. However, a consequence of observing seals remotely meant that information on sex, maturity‐stage, or breeding status was not always available. To provide unbiased estimates of survival rates we conditioned initial release of individuals on the first time sex was known to estimate sex‐specific survival rates, while a robust design multistate model accounting for uncertainty in breeding status was used to estimate reproductive rate of multiparous and ≥3‐yr‐old females. Survival rates were estimated at 0.95 (95% CI = 0.91–0.97) for females and 0.92 (0.83–0.96) for males, while reproductive rate was estimated at 0.89 (0.75–0.95) for multiparous and 0.69 (0.64–0.74) for ≥3‐yr‐old females. Stage‐based population modeling indicated that this population should be recovering, even under the current shooting quotas implemented by the recent management plan.     

Swimming against the tide: resilience of a riverine turtle to recurrent extreme environmental events

Extreme environmental events (EEEs) are likely to exert deleterious effects on populations. From 1996 to 2012 we studied the nesting dynamics of a riverine population of painted turtles (Chrysemys picta) that experienced seven years with significantly definable spring floods. We used capture–mark–recapture methods to estimate the relationships between more than 5 m and more than 6 m flood events and population parameters. Contrary to expectations, flooding was not associated with annual differences in survival, recruitment or annual population growth rates of the adult female segment of the population. These findings suggest that female C. picta exhibit resiliency to key EEE, which are expected to increase in frequency under climate change.     

Sex- and age-dependent effects of population density on life history traits of red deer Cervus elaphus in a temperate forest

We studied both the short‐ and long‐term effects of density on three life history traits of a red deer population inhabiting a temperate forest. Both male and female body mass increased when population density decreased, but male mass changed to a greater extent than female mass. Density did not influence female survival irrespective of age, however, survival of males was lower at high density for all age classes except the prime‐age class. Pregnancy rates of primiparous females increased markedly with decreasing density, whereas those of adult hinds were fairly constant and unrelated to density. For both sexes, of the studied life history traits we detected a long‐term effect of density at birth (cohort effect) only on body mass. These results suggest that density influences life history traits in the same way as factors of environmental variation such as climate. In this population we did not find any evidence for an influence of climatic conditions on life history traits of red deer. Both mild winters and the absence of summer droughts during the study period could account for such an absence of climatic effects. We interpreted our results to show that 1) as expected for a highly dimorphic and polygynous species such as red deer, male traits showed consistently higher sensitivity to variation in density than female traits, illustrating possible costs caused by sexual selection in males, 2) the female‐based Eberhardt's model according to which increasing density should sequentially affect juvenile survival, reproductive rates of primiparous females, reproductive rates of adults and lastly adult survival was only partly supported because we found that pregnancy rate of primiparous females rather than juvenile survival was the most sensitive trait to variation in density. We propose that including variation in male traits would improve the accuracy of models of population dynamics of large mammals, at least for highly dimorphic species. Because the population we studied was not fenced, we only measured apparent survival. We discuss how dispersal, in relation to the phenotypic quality of young deer, might be a potential regulating factor under such conditions.     

Variation in probability of first reproduction of Weddell seals

1. For many species, when to begin reproduction is an important life-history decision that varies by individual and can have substantial implications for lifetime reproductive success and fitness. 2. We estimated age-specific probabilities of first-time breeding and modelled variation in these rates to determine age at first reproduction and understand why it varies in a population of Weddell seals in Erebus Bay, Antarctica. We used multistate mark-recapture modelling methods and encounter histories of 4965 known-age female seals to test predictions about age-related variation in probability of first reproduction and the effects of annual variation, cohort and population density. 3. Mean age at first reproduction in this southerly located study population (7.62 years of age, SD=1.71) was greater than age at first reproduction for a Weddell seal population at a more northerly and typical latitude for breeding Weddell seals (mean=4-5 years of age). This difference suggests that age at first reproduction may be influenced by whether a population inhabits the core or periphery of its range. 4. Age at first reproduction varied from 4 to 14 years, but there was no age by which all seals recruited to the breeding population, suggesting that individual heterogeneity exists among females in this population. 5. In the best model, the probability of breeding for the first time varied by age and year, and the amount of annual variation varied with age (average variance ratio for age-specific rates=4.3%). 6. Our results affirmed the predictions of life-history theory that age at first reproduction in long-lived mammals will be sensitive to environmental variation. In terms of life-history evolution, this variability suggests that Weddell seals display flexibility in age at first reproduction in order to maximize reproductive output under varying environmental conditions. Future analyses will attempt to test predictions regarding relationships between environmental covariates and annual variation in age at first reproduction and evaluate the relationship between age at first reproduction and lifetime reproductive success.     

Global climate patterns explain range-wide synchronicity in survival of a migratory seabird

To predict the impact of climate change over the whole species distribution range, comparison of adult survival variations over large spatial scale is of primary concern for long-lived species populations that are particularly susceptible to decline if adult survival is reduced. In this study, we estimated and compared adult survival rates between 1989 and 1997 of six populations of Cory's shearwater ( Calonectris diomedea ) spread across 4600 km using capture–recapture models. We showed that mean annual adult survival rates are different among populations along a longitudinal gradient and between sexes. Variation in adult survival is synchronized among populations, with three distinct groups: (1) both females and males of Corsica, Tremiti, and Selvagem (annual survival range 0.88–0.96); (2) both females and males of Frioul and females from Crete (0.82–0.92); and (3) both females and males of Malta and males from Crete (0.74–0.88). The total variation accounted for by the common pattern of variation is on average 71%, suggesting strong environmental forcing. At least 61% of the variation in survival is explained by the Southern Oscillation Index fluctuations. We suggested that Atlantic hurricanes and storms during La Niña years may increase adult mortality for Cory's shearwater during winter months. For long-lived seabird species, variation in adult survival is buffered against environmental variability, although extreme climate conditions such as storms significantly affect adult survival. The effect of climate at large spatial scales on adult survival during the nonbreeding period may lead to synchronization of variation in adult survival over the species' range and has large effects on the meta-population trends. One can thus worry about the future of such long-lived seabirds species under the predictions of higher frequency of extreme large-scale climatic events.     

Observational evidence of risk-sensitive reproductive allocation in a long-lived mammal

Organisms should adopt a risk-sensitive reproductive allocation when summer reproductive allocation competes with survival in the coming winter. This trade off is shown through autumn female body mass, which acts as an insurance against unpredictable winter environmental conditions. We tested this hypothesis on female reindeer in a population that has experienced a time period of dramatic increase in abundance. Environmental conditions during winter were fairly stable (with the exception of 1 year). We conclude that increased population abundance (perhaps in interaction with winter environmental conditions) could have represented a worsening of winter environmental conditions as both autumn offspring and spring female body mass decreased during the course of the study. Moreover, we found that the cost of reproduction was related to environmental conditions as: (1) autumn body mass was larger for barren than for lactating females, and this difference was temporally highly variable; (2) lactating females produced smaller offspring than barren ones in the following year; and (3) reproductive output (offspring size) decreased over time. We also found evidence of quality effects as lactating females had a higher reproductive success in the following year. In sum, a worsening of winter conditions lead to: (1) decreased reproductive output; (2) lowered autumn body mass for lactating females; and (3) increased body mass for barren females. Since females reduce their reproductive allocation as winter conditions becomes more severe, we conclude that reindeer have adopted a risk-sensitive reproductive allocation.     

Negligible effects of blood sampling on reproductive performance and return rates of Tree Swallows

Blood sampling is a frequently used method of collecting genetic and physiological data in natural populations, and understanding the possible impact of blood sampling on individuals and populations is important, both for the welfare of study organisms and to avoid introducing bias into analyses using bled individuals. Most studies of birds have revealed minimal negative effects of blood sampling. However, Brown and Brown (2009. Auk 126: 853–861) found that blood sampling reduced return rates of Cliff Swallows (Petrochelidon pyrrhonota), suggesting that these results are not always generalizable and that swallows (Hirundinidae) may be particularly sensitive to blood sampling. We examined the possible effects of blood sampling on the reproductive performance of female Tree Swallows (Tachycineta bicolor) and the return rates of both females and offspring in a population in New York state. To reduce the chances of Type II error, we tested 15 possible effects of blood sampling on reproductive performance and return rates using generalized linear mixed models. Overall, our results suggest that blood sampling had few negative effects on within‐year reproductive success or survival of adult females. The one exception was that bleeding nestlings had a negative effect on the number of young that fledged in broods of five or six nestlings. Bleeding did not negatively impact return rates of females or nestlings in our Tree Swallow population. Our results support those of other studies suggesting that blood sampling has few negative effects on within‐year reproductive success or survival of adult females, and reiterate the importance of systematically testing for possible effects with datasets compiled over multiple years because such effects may be impossible to detect via direct monitoring during a single breeding season.     

Slow life history and rapid extreme flood: demographic mechanisms and their consequences on population viability in a threatened amphibian

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Cyst bank life-history model for a fairy shrimp from ephemeral ponds

1. Ephemeral wetland habitats provide a useful model system for studying how life‐history patterns enable populations to persist despite high environmental variation. One important life‐history trait of both plants and crustaceans in such habitats involves hatching/germination of only some of the eggs/seeds at any time. This bet‐hedging leads to the development of a bank composed of dormant propagules of many ages. 2. The San Diego fairy shrimp, Branchinecta sandiegonensis (Crustacea: Anostraca), a dominant faunal element of ephemeral ponds in San Diego, California, is a suitable organism for studying the consequences of highly fluctuating environmental conditions. As a result of large‐scale habitat loss, the species is also endangered, and this motivated our specific study towards understanding the hatching dynamics of its egg bank for planning conservation efforts such as pool restoration and re‐creation. 3. We formulated a matrix population model using egg age within the bank to study the relationship between adult survival and reproduction, and survival in and hatching from the egg bank. As vital rates for fairy shrimp are only poorly known, we generated 48 matrices with parameters encompassing ranges of likely values for the vital rates of B. sandiegonensis. We calculated population growth rates and eigenvalue elasticities both for a static model and a model with periodic reproductive failure. 4. The model shows that in good filling events, population growth rate is very high and the egg bank is increased dramatically. While population growth rate is insensitive to long‐term survival in the egg bank in our static deterministic model, it becomes sensitive to survival in the egg bank when a regime of periodically failed reproductive events is imposed. 5. Under favourable conditions, it was best for shrimp to hatch from eggs as soon as possible. However, under a regime where failed reproductive events were common, it was best to hatch after several pool fillings. Because conditions change from favourable to unfavourable unpredictably, variation in age within the egg bank appears to be critical for the persistence of the population. This attribute needs to be carefully considered when restoring or creating new pools for conservation purposes.     

Phenological variation in annual timing of hibernation and breeding in nearby populations of Arctic ground squirrels

Ecologists need an empirical understanding of physiological and behavioural adjustments that animals can make in response to seasonal and long-term variations in environmental conditions. Because many species experience trade-offs between timing and duration of one seasonal event versus another and because interacting species may also shift phenologies at different rates, it is possible that, in aggregate, phenological shifts could result in mismatches that disrupt ecological communities. We investigated the timing of seasonal events over 14 years in two Arctic ground squirrel populations living 20 km apart in Northern Alaska. At Atigun River, snow melt occurred 27 days earlier and snow cover began 17 days later than at Toolik Lake. This spatial differential was reflected in significant variation in the timing of most seasonal events in ground squirrels living at the two sites. Although reproductive males ended seasonal torpor on the same date at both sites, Atigun males emerged from hibernation 9 days earlier and entered hibernation 5 days later than Toolik males. Atigun females emerged and bred 13 days earlier and entered hibernation 9 days earlier than those at Toolik. We propose that this variation in phenology over a small spatial scale is likely generated by plasticity of physiological mechanisms that may also provide individuals the ability to respond to variation in environmental conditions over time.     

Age-specific cost of first reproduction in female southern elephant seals

When to commence breeding is a crucial life-history decision that may be the most important determinant of an individual''s lifetime reproductive output and can have major consequences on population dynamics. The age at which individuals first reproduce is an important factor influencing the intensity of potential costs (e.g. reduced survival) involved in the first breeding event. However, quantifying age-related variation in the cost of first reproduction in wild animals remains challenging because of the difficulty in reliably recording the first breeding event. Here, using a multi-event capture–recapture model that accounts for both imperfect detection and uncertainty in the breeding status on an 18-year dataset involving 6637 individuals, we estimated age and state-specific survival of female elephant seals (Mirounga leonina) in the declining Macquarie Island population. We detected a clear cost of first reproduction on survival. This cost was higher for both younger first-time breeders and older first-time breeders compared with females recruiting at age four, the overall mean age at first reproduction. Neither earlier primiparity nor delaying primiparity appear to confer any evolutionary advantage, rather the optimal strategy seems to be to start breeding at a single age, 4 years.     

Sea turtle nesting distributions and oceanographic constraints on hatchling migration

Patterns of abundance across a species''s reproductive range are influenced by ecological and environmental factors that affect the survival of offspring. For marine animals whose offspring must migrate long distances, natural selection may favour reproduction in areas near ocean currents that facilitate migratory movements. Similarly, selection may act against the use of potential reproductive areas from which offspring have difficulty emigrating. As a first step towards investigating this conceptual framework, we analysed loggerhead sea turtle (Caretta caretta) nest abundance along the southeastern US coast as a function of distance to the Gulf Stream System (GSS), the ocean current to which hatchlings in this region migrate. Results indicate that nest density increases as distance to the GSS decreases. Distance to the GSS can account for at least 90 per cent of spatial variation in regional nest density. Even at smaller spatial scales, where local beach conditions presumably exert strong effects, at least 38 per cent of the variance is explained by distance from the GSS. These findings suggest that proximity to favourable ocean currents strongly influences sea turtle nesting distributions. Similar factors may influence patterns of abundance across the reproductive ranges of diverse marine animals, such as penguins, eels, salmon and seals.     

Effects of temperature on two Mediterranean population of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): II. Effects on demographic parameters

The effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus, the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts.Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 °C in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 °C is counter-balanced by the early attainment of sexual maturity induced at 30 °C. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus.     

Facultative semelparity in capelin Mallotus villosus (Osmeridae)-an experimental test of a life history phenomenon in a sub-arctic fish

Two alternative reproductive modes are present in fishes and reflect the age-specific mortality encountered through ontogenesis. Life-history hypotheses suggest that semelparity (i.e. death after a single reproductive event) evolves when the ratio of juvenile to adult survival is relatively high. Conversely, a relatively low ratio of juvenile to adult survival will favour iteroparity (i.e. death after two or more reproductive events). Fisheries management associates capelin (Mallotus villosus) spawning with mass mortality and semelparity even though life history models developed for this species suggest that females may follow an iteroparous trajectory. Capelin may spawn either inter-tidally on the beach or offshore in deeper, ocean waters but post-spawning survival and potential iteroparity has been notoriously difficult to assess in natural populations. Through a series of aquarium experiments we tested post-spawning survivability in a beach spawning and an ocean spawning population. The findings demonstrate that capelin which spawn offshore are absolute semelparous (death of both genders) while beach spawning capelin are iteroparous irrespective of sex. Beach spawning capelin regenerated ripe gonads from one spawning season to the next and provides the first conclusive evidence that capelin is physiologically capable of an iteroparous reproductive mode. The potential physical and biological processes which generate certain reproductive patterns in capelin are summarized and discussed in relation to life history hypotheses. We suggest that capelin is a facultative semelparous species in which dynamic changes within the semelparity-iteroparity continuum may occur as a result of subtle interactions between the spawning habitat, physical forcing, and predatory pressure.     

Mechanisms and reproductive consequences of breeding dispersal in a specialist predator under temporally varying food conditions

Individual variation in breeding dispersal has extensive ecological and evolutionary consequences, but the factors driving individual dispersal behaviour and their fitness consequences remain poorly understood. Our data on dispersal events of a rodent‐specialist predator, the Eurasian kestrel Falco tinnunculus, over 20 years in western Finland offers a unique opportunity to explore the mechanisms underlying breeding dispersal behaviour and its reproductive consequences in a wild bird population. Sex, age, body condition and previous breeding success affected breeding dispersal. Dispersal distances were longer in females than in males as well as longer in yearlings than in older individuals. Body condition was positively correlated to breeding dispersal distances, particularly for females. The lowest dispersal distances were recorded for intermediate brood sizes in the year preceding dispersal. Our results highlight sex‐ and environment‐specific consequences of breeding dispersal on reproductive performance. During increase phases of the three‐year vole cycles, males dispersing further had lower reproductive performance after dispersal, whereas in females, long breeding dispersal distances were associated with increased breeding success under all environmental conditions. These results suggest benefits associated to breeding dispersal in females, potentially related to large spatio‐temporal variation in main food abundance and intensity of intra‐specific competition. Breeding dispersal of males was costly during increasing food abundance, indicating the potential fitness benefits of environmental familiarity in this migratory species. Overall, our results indicate that both individual traits and environmental factors interact to shape breeding dispersal strategies in wide‐ranging predator populations under fluctuating food conditions.