Offspring size–number tradeoffs and food quality feedbacks impact population dynamics in a Daphnia–algae system

Population fluctuations can be affected by both extrinsic (e.g. weather patterns, food availability) and intrinsic (e.g. life‐history) factors. A key life‐history tradeoff is the production of offspring size versus number, ranging from many small offspring to few large offspring. Models show that this life‐history tradeoff in offspring size and number, through maturation time, can have significant impacts on population dynamics. However, few manipulative experiments have been conducted that can isolate life‐history effects from impacts of extrinsic factors in consumer–resource systems. We experimentally tested the effect of an offspring size–number tradeoff on population stability and food availability in a consumer–resource system. Using Daphnia pulex, we created a shift from many, small offspring being produced to fewer, larger offspring. Two sets of experiments were performed to examine the interaction of an extrinsic factor (light levels) and intrinsic population structure on dynamics, and we controlled for the ingestion pressure on algal prey at the time of the manipulation. We predicted that the tradeoff would impact internal consumer population characteristics, including biasing the stage structure towards adults, increasing adult size, and increasing average population‐level reproduction. This adult‐dominated stage structure was predicted to then lead to instability and a low quantity–high quality food state. Under all light levels, the manipulated populations became dominated by large adults. Contrary to predictions, the amplitudes of fluctuations in Daphnia biomass were lower in populations shifted to few–large offspring, representing higher stability in these populations. Furthermore, in high light conditions, a stable low Daphnia – high algae biomass (low food quality) state was observed in few–large offspring treatments but not in control (many–small offspring) treatments. Our results show a strong link between light levels as an extrinsic factor and the life‐history tradeoff of consumer offspring size versus number that impacts consumer–resource population dynamics through feedbacks with resource quality.     

The Worldwide Variation in Avian Clutch Size across Species and Space

Traits such as clutch size vary markedly across species and environmental gradients but have usually been investigated from either a comparative or a geographic perspective, respectively. We analyzed the global variation in clutch size across 5,290 bird species, excluding brood parasites and pelagic species. We integrated intrinsic (morphological, behavioural), extrinsic (environmental), and phylogenetic effects in a combined model that predicts up to 68% of the interspecific variation in clutch size. We then applied the same species-level model to predict mean clutch size across 2,521 assemblages worldwide and found that it explains the observed eco-geographic pattern very well. Clutches are consistently largest in cavity nesters and in species occupying seasonal environments, highlighting the importance of offspring and adult mortality that is jointly expressed in intrinsic and extrinsic correlates. The findings offer a conceptual bridge between macroecology and comparative biology and provide a global and integrative understanding of the eco-geographic and cross-species variation in a core life-history trait.     

Reproductive plasticity, ovarian dynamics and maternal effects in response to temperature and flight in Pararge aegeria

In nature, ovipositing females may be subjected to multiple extrinsic and intrinsic environmental factors simultaneously. To adequately assess a species response to environmental conditions during oviposition it may therefore be necessary to consider the interaction between multiple intrinsic and extrinsic factors simultaneously. Using the butterfly, Pararge aegeria, this study examined the combined effects of extrinsic (temperature and flight) and intrinsic (body mass and age) factors on ovarian dynamics, egg provisioning and reproductive output, and explored how these effects subsequently influenced offspring fitness when egg-stage development occurred in a low humidity environment. Both temperature- and flight-mediated plasticity in female reproductive output was observed, and there were strong temperature by flight interaction effects for the traits oocyte size and egg mass. As females aged, mean daily fecundity differed across temperature treatments, but not across flight treatments. Overall, temperature had more pronounced effects on ovarian dynamics than flight. Flight mainly influenced egg mass via changes in relative water content. A mismatch between the physiological response of females to high temperature and the requirements of their offspring had a negative impact on offspring fitness via effects on egg hatching success.     

Song complexity is associated with habitat quality in an upland passerine

Understanding the influence of intrinsic (genetic and morphological) and extrinsic (geographical, environmental and social) factors on the performance and spatial differentiation of sexual signals, such as bird song, can help identify behavioural indicators of individual quality, habitat degradation and social environment. We used the Iberian Bluethroat Luscinia svecica azuricollis, a migratory bird that breeds in fragmented landscapes dominated by shrublands, as a case study to: (1) assess how a set of acoustic indicators of song performance are driven by intrinsic and extrinsic factors; and (2) contrast deterministic (adaptations to the environmental context and morphological constraints) vs. stochastic (differentiation by geographical isolation) explanations for song differentiation patterns. We explored acoustic indicators of song performance (spectral, temporal and song complexity) in relation to parameters related to genetic structure, body size, habitat type, habitat quality (assessed through a spatially explicit modelling approach) and social context (population abundance and songbird community composition). Then, we explored the contribution of genetic, geographical and environmental dissimilarity to song diversification across space. Our results highlight an association of song spectral variables with genetic structure and a significant connection between song complexity and duration with habitat quality. We found no relationship between social features and acoustic variables, or between song differentiation and genetic or geographical distances. There was, however, a correlation between song differentiation and environmental dissimilarity. We recommend the consideration of song complexity as an indicator of habitat quality.     

Ecologically dependent and intrinsic genetic signatures of postzygotic isolation between sympatric host races of the leaf beetle Lochmaea capreae

The fitness of hybrids might be compromised as a result of intrinsic isolation and/or because they fall between ecological niches due to their intermediate phenotypes (“extrinsic isolation”). Here, we present data from several crosses (parental crosses, F1, F2, and backcrosses) between the two host races of Lochmaea capreae on willow and birch to test for extrinsic isolation, intrinsic isolation, and environmentally dependent genetic incompatibilities. We employed a reciprocal transplant design in which offspring were raised on either host plant and their survival was recorded until adulthood. We also applied joint‐scaling analysis to determine the genetic architecture of hybrid inviability. The relative fitness of the backcrosses switched between environments; furthermore, the additive genetic–environment interaction was detected as the strongest effect in our analysis. These results provide strong evidence that divergent natural selection has played a central role in the evolution of hybrid dysfunction between host races. Joint‐scaling analysis detected significant negative epistatic effects that are most evident in the poor performance of F2‐hybrids on willow, indicating signs of intrinsic isolation. We did not find any evidence that genetic incompatibilities are manifested independently of environmental conditions. Our findings suggest the outcome of natural hybridization between these host races is mainly affected by extrinsic isolation and a weak contribution of intrinsic isolation.     

Intrinsic post‐ejaculation sperm ageing does not affect offspring fitness in Atlantic salmon

Post‐meiotic sperm ageing, both before ejaculation and after ejaculation, has been shown to negatively affect offspring fitness by lowering the rate of embryonic development, reducing embryonic viability and decreasing offspring condition. These negative effects are thought to be caused by intrinsic factors such as oxidative stress and ATP depletion or extrinsic factors such as temperature and osmosis. Effects of post‐ejaculation sperm ageing on offspring fitness have so far almost exclusively been tested in internal fertilizers. Here, we tested whether intrinsic post‐ejaculation sperm ageing affects offspring performance in an external fertilizer, the Atlantic salmon Salmo salar. We performed in vitro fertilizations with a split‐clutch design where sperm were subjected to four post‐ejaculation ageing treatments. We varied the duration between sperm activation and fertilization while minimizing extrinsic stress factors and tested how this affected offspring fitness. We found no evidence for an effect of our treatments on embryo survival, hatching time, larval standard length, early larval survival or larval growth rate, indicating that intrinsic post‐ejaculation sperm ageing may not occur in Atlantic salmon. One reason may be the short life span of salmon sperm after ejaculation. Whether our findings are true in other external fertilizers with extended sperm activity remains to be tested.     

Long-term shifts in the cyclicity of outbreaks of a forest-defoliating insect

Optimisation of reproductive investment is crucial for Darwinian fitness, and detailed long-term studies are especially suited to unravel reproductive allocation strategies. Allocation strategies depend on the timing of resource acquisition, the timing of resource allocation, and trade-offs between different life-history traits. A distinction can be made between capital breeders that fuel reproduction with stored resources and income breeders that use recently acquired resources. In capital breeders, but not in income breeders, energy allocation may be decoupled from energy acquisition. Here, we tested the influence of extrinsic (weather conditions) and intrinsic (female characteristics) factors during energy storage, vitellogenesis and early gestation on reproductive investment, including litter mass, litter size, offspring mass and the litter size and offspring mass trade-off. We used data from a long-term study of the viviparous lizard, Lacerta (Zootoca) vivipara. In terms of extrinsic factors, rainfall during vitellogenesis was positively correlated with litter size and mass, but temperature did not affect reproductive investment. With respect to intrinsic factors, litter size and mass were positively correlated with current body size and postpartum body condition of the previous year, but negatively with parturition date of the previous year. Offspring mass was negatively correlated with litter size, and the strength of this trade-off decreased with the degree of individual variation in resource acquisition, which confirms theoretical predictions. The combined effects of past intrinsic factors and current weather conditions suggest that common lizards combine both recently acquired and stored resources to fuel reproduction. The effect of past energy store points out a trade-off between current and future reproduction.     

Maternal influences on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination

Maternal and environmental factors are important sources of phenotypic variation because both factors influence offspring traits in ways that impact offspring and maternal fitness. The present study explored the effects of maternal factors (maternal body size, egg size, yolk‐steroid allocation, and oviposition‐site choice) and seasonally‐variable environmental factors on offspring phenotypes and sex ratios in a multi‐clutching lizard with environmental sex determination (Amphibolurus muricatus). Maternal identity had strong effects on offspring morphology, but the nature of maternal effects differed among successive clutches produced by females throughout the reproductive season (i.e. maternal identity by environment interactions). The among‐female and among‐clutch variation in offspring traits (including sex ratios) was not mediated through maternal body size, egg size, or variation in yolk steroid hormones. This lack of nongenetic maternal effects suggests that phenotypic variation may be generated by gene by environment interactions. These results demonstrate a significant genetic component to variation in offspring phenotypes, including sex ratios, even in species with environmental sex determination. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 256–266.     

Geographic variation in primary sex allocation per flower within and among 12 species of Pedicularis (Orobanchaceae): Proportional male investment increases with elevation

? Premise of the study: The study of geographic variation in ecologically important traits within and among taxa is a first step toward understanding the environmental factors that contribute to population differentiation and species divergence. This study examines variation in mean sex allocation per flower (androecium mass/gynoecium mass) among 49 wild populations representing 12 Pedicularis species across an elevation gradient on the eastern Tibetan Plateau. ? Methods: We used population means to evaluate sources of variation in per-flower sex allocation within and across species. In particular, we evaluate the relative influence of intrinsic (i.e., plant size, estimated as aboveground stem biomass) vs. extrinsic factors affecting mean sex allocation among populations. ? Key results: Mean sex allocation per flower (the relative investment in male floral organs) is negatively correlated with mean plant size; populations of large plants produce relatively female-biased flowers. This relationship between mean plant size and mean sex allocation is not statistically significant, however, when the effect of elevation is controlled statistically. Among populations within and across species, mean sex allocation increases with elevation. This relationship persists even when the effect of mean plant size is controlled statistically. Factors associated with increasing elevation appear to favor genotypes and/or taxa with male-biased flowers. ? Conclusion: Extrinsic environmental conditions may be more important than intrinsic resource status in determining patterns of geographic variation in mean sex allocation among populations or species of Pedicularis. We cannot conclude whether the effect of elevation on mean sex allocation is the result of environmentally induced plasticity, genetically based adaptation, or species sorting, but it is only partly mediated by mean plant size.     

Primary floral allocation per flower in 12 <Emphasis Type="Italic">Pedicularis</Emphasis> (Orobanchaceae) species: significant effect of two distinct rewarding types for pollinators

For animal-pollinated hermaphrodite plants, the factors that affect floral allocation were usually assigned to extrinsic (environment) and intrinsic ones (resources status). Few studies focused on the effect of rewarding type of plants (pollen vs. nectar and pollen). In this study, we investigated the variation in floral allocation per flower with respect to two distinct rewarding types for pollinators in 12 Pedicularis species in alpine regions, testing for the effects of species, plant size, and elevation simultaneously. The result showed that the rewarding type affected floral allocation significantly, and there was a female-biased floral allocation pattern in nectarless rewarding species relative to nectar and pollen rewarding ones and provided a new insight into variation in floral allocation. It was discussed with respect to activities and foraging behavior of pollinators on the basis of sex allocation theory. Moreover, environmental conditions (elevation) may also play a relatively important role in determining patterns of variation in floral allocation per flower, whereas plant size may not.     

Population ecology and conservation of endangered megafauna: the case of European bison in Białowieża Primeval Forest, Poland

The European bison Bison bonasus is an example of nearly extinct 'charismatic megafauna'. The Białowieża Primeval Forest in Poland is among the few places where they still live in the wild. The management of this free-living herd has to reconcile to the conservation needs of a species and the economic and environmental objectives of their habitat: protected as well as commercial woodlands of Białowieża. Here we present a detailed account of the population development and analyse variation in vital rates based on monitoring that started in 1952 and continued until 2002. The population was allowed to grow freely until 1970, when removal started with the aim to stabilize population size. We found that recruitment rate, but not mortality, was density dependent, suggesting that the population density was not very high relative to resource levels. Winters with much snow and cold temperature had a strong negative effect on survival. May temperature of the previous year positively affected recruitment rates. Masting (oak seed) also positively affected recruitment rates, which provides a rare account of masting affecting the performance of a large ruminant. Sex ratio of offspring was even and was not strongly affected by density or climate. We use an age-structured matrix model to show how this knowledge of intrinsic and extrinsic factors affecting vital rates may help managerial decisions by providing explicit links between given environmental conditions and the population growth rates.     

Maternal investment in egg size: environment- and population-specific effects on offspring performance

Geographic variation in maternal investment in offspring size can be adaptive if differences in investment translate into improved offspring performance in the given environments. We compared two moor frog, Rana arvalis, populations in the laboratory to test the hypothesis that investment in large eggs in populations originating from stressful (acid) environments improves offspring performance when reared in stressful (acid) conditions. We found that large initial size (hatchling mass) had moderate to strong, environment-dependent positive effects on larval and metamorphic traits in the acidic origin population, but only weak effects in the neutral origin population. Our results suggest that interactions between environmental conditions and initial size can be important determinants of individual performance, and that investment in large eggs is adaptive in acid environments. These findings emphasize the role of maternal effects as adaptations to environmental stress.     

Intrinsic and Extrinsic Factors Influence Expression of Defensive Behavior in Plains Hog‐Nosed Snakes (Heterodon nasicus)

Animals failing to deter predation are eaten. Among the many deterrents to predation, antipredator behaviors are perhaps the most variable, ranging from active (fight or flight) to passive (immobility). We assessed variation in the expression of a passive defensive behavior, death‐feigning, in Plains Hog‐nosed Snakes (Heterodon nasicus) and predicted that intrinsic and extrinsic factors would influence the duration of this behavior and the latency to its onset. We simulated predatory attacks on 27 snakes encountered in the field, and analyzed the behavioral responses of snakes as a function of differences among individuals (sex and size) and environmental factors (temperature and microhabitat). Larger snakes death‐feigned for longer durations than smaller ones; this relationship was stronger for female snakes than for males. Death feints were initiated sooner when snakes were encountered at higher temperatures. Extrinsic factors had a greater influence on latency to death‐feigning behavior, whereas intrinsic factors more strongly influenced its duration. Because our results involved wild snakes, they provide an improved, highly relevant understanding of individual and environmental factors that regulate the expression of immobile defensive behavior. Furthermore, additional hypotheses can now be proposed that address the evolution of defensive behaviors that leave animals prone to attack.     

Changes in seasonal climate outpace compensatory density‐dependence in eastern brook trout

Understanding how multiple extrinsic (density‐independent) factors and intrinsic (density‐dependent) mechanisms influence population dynamics has become increasingly urgent in the face of rapidly changing climates. It is particularly unclear how multiple extrinsic factors with contrasting effects among seasons are related to declines in population numbers and changes in mean body size and whether there is a strong role for density‐dependence. The primary goal of this study was to identify the roles of seasonal variation in climate driven environmental direct effects (mean stream flow and temperature) vs. density‐dependence on population size and mean body size in eastern brook trout (Salvelinus fontinalis). We use data from a 10‐year capture‐mark‐recapture study of eastern brook trout in four streams in Western Massachusetts, USA to parameterize a discrete‐time population projection model. The model integrates matrix modeling techniques used to characterize discrete population structures (age, habitat type, and season) with integral projection models (IPMs) that characterize demographic rates as continuous functions of organismal traits (in this case body size). Using both stochastic and deterministic analyses we show that decreases in population size are due to changes in stream flow and temperature and that these changes are larger than what can be compensated for through density‐dependent responses. We also show that the declines are due mostly to increasing mean stream temperatures decreasing the survival of the youngest age class. In contrast, increases in mean body size over the same period are the result of indirect changes in density with a lesser direct role of climate‐driven environmental change.     

Of Monkeys and Men: A Metabolomic Analysis of Static and Dynamic Urinary Metabolic Phenotypes in Two Species

Background

Metabolomics has attracted the interest of the medical community for its potential in predicting early derangements from a healthy to a diseased metabolic phenotype. One key issue is the diversity observed in metabolic profiles of different healthy individuals, commonly attributed to the variation of intrinsic (such as (epi)genetic variation, gut microbiota, etc.) and extrinsic factors (such as dietary habits, life-style and environmental conditions). Understanding the relative contributions of these factors is essential to establish the robustness of the healthy individual metabolic phenotype.

Methods

To assess the relative contribution of intrinsic and extrinsic factors we compared multilevel analysis results obtained from subjects of Homo sapiens and Macaca mulatta, the latter kept in a controlled environment with a standardized diet by making use of previously published data and results.

Results

We observed similarities for the two species and found the diversity of urinary metabolic phenotypes as identified by nuclear magnetic resonance (NMR) spectroscopy could be ascribed to the complex interplay of intrinsic factors and, to a lesser extent, of extrinsic factors in particular minimizing the role played by diet in shaping the metabolic phenotype. Moreover, we show that despite the standardization of diet as the most relevant extrinsic factor, a clear individual and discriminative metabolic fingerprint also exists for monkeys. We investigate the metabolic phenotype both at the static (i.e., at the level of the average metabolite concentration) and at the dynamic level (i.e., concerning their variation over time), and we show that these two components sum up to the overall phenotype with different relative contributions of about 1/4 and 3/4, respectively, for both species. Finally, we show that the great degree diversity observed in the urinary metabolic phenotype of both species can be attributed to differences in both the static and dynamic part of their phenotype.     

Evolution of life‐history traits in geographically isolated populations of Vaejovis scorpions (Scorpiones: Vaejovidae)

Geographical isolation can over time accumulate life‐history variation which can eventually lead to speciation. We used five species of Vaejovis scorpions that have been isolated from one another since the Pleistocene glaciation to identify if biogeographical patterns have allowed for the accumulation of life‐history variation among species. Gravid females were captured and brought back to the lab until giving birth. Once offspring had begun to disperse, measurements of female size, reproductive investment, offspring size, offspring number, and variation in offspring size were recorded. Differences in how each species allocated energy to these variables were analysed utilizing path analysis and structural equation modelling. Female and offspring size, litter size, and total litter mass differed among species, but relative energetic investment did not. Most significant differences among species were not present after removing the effect of female size, indicating that female size is a major source of life‐history variation. Path analyses indicated that there was no size–number trade‐off within any species and that each species allocates energy toward total litter mass differently. Additionally, as offspring size increased, the variation in offspring mass decreased. These results show that each species allocates the same relative amount of energy in different ways. The variation seen could be a response to environmental variability or uncertainty, a product of maternal effects, or caused by the sufficient accumulation of genetic differences due to geographical isolation. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 715–727.     

Geographic variation in hatchling size in an oviparous skink: effects of maternal investment and incubation thermal environment

Geographic variation in offspring size can be viewed as an adaptive response to local environmental conditions, but the causes of such variation remain unclear. Here, we compared the size and composition of eggs laid by female Chinese skinks (Plestiodon chinensis) from six geographically distinct populations in southeastern China to evaluate geographic variation in hatchling size. We also incubated eggs from these six populations at three constant temperatures (24, 28 and 32 °C) to evaluate the combined effects of incubation temperature and population source on hatchling size. Egg mass and composition varied among populations, and interpopulation differences in yolk dry mass and energy content were still evident after accounting for egg mass. Population mean egg mass and thus hatchling mass were greater in the colder localities. Females from three northern populations increased offspring size by laying larger eggs relative to their own size. Females from an inland population in Rongjiang could increase offspring size by investing relatively more dry materials and thus more energy into individual eggs without enlarging the size of their eggs. The degree of embryonic development at oviposition was almost the same across the six populations, so was the rate of embryonic development and thus incubation length at any given temperature. Both incubation temperature and population source affected hatchling traits examined, but the relative importance of these two factors varied between traits. Our data show that in P. chinensis hatchling traits reflecting overall body size (body mass, snout‐vent length and tail length) are more profoundly affected by population source. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 283–296.     

Influence of hybridization on animal space use: a case study using coyote range expansion

Hybridization between animal species is likely to increase as distributional and reproductive barriers continue to break down due to anthropogenically driven changes in habitat and climate. Yet, the influence of hybridization on ecological interactions and ecosystem function remains understudied. Animal space use, an important component of ecosystem dynamics, is a complex relationship between intrinsic factors, which hybridization can influence, and extrinsic factors, such as environmental heterogeneity. Using the coyote Canis latrans, a well‐studied species with a long history of hybridization with wolves and dogs Canis spp., we sought to assess the influence of hybridization relative to environmental factors in determining animal space use. We conducted a meta‐regression analysis of 67 datasets on coyote home range size across North America and generated models to predict coyote home range size. Climate (latitude) and environmental variability played important roles in determining patterns of coyote space use, likely through their influence on availability of prey resources. However, we found hybridization to be the preeminent factor driving variation in coyote space use, with non‐introgressed populations having considerably smaller home ranges than those from within the Canis hybrid zone of eastern North America. This pattern was upheld despite the variation in environmental factors between areas inside and outside the Canis hybrid zone. Our findings suggest that hybridization may serve as an important factor affecting ecosystems, as hybrids may have altered space requirements, and presumably different niche dimensions, compared to parental species. This, in turn, may influence the role that particular species play within communities. Synthesis Hybridization between animal species is likely to increase due to anthropogenically driven changes in habitat and climate. We used a meta‐regression analysis (n = 67) to examine the relationship between hybridization and coyote Canis latrans space use across North America. We found that independent of environmental factors, introgressed coyotes had larger home ranges. Our findings suggest that hybridization may serve as an important factor affecting ecosystems, as hybrids may have altered space requirements, and presumably different niche dimensions, compared to parental species. This, in turn, may influence the role that particular species play within communities.     

Inter‐annual variability and long‐term trends in breeding success in a declining population of migratory swans

Population declines among migratory Arctic‐breeding birds are a growing concern for conservationists. To inform the conservation of these declining populations, we need to understand how demographic rates such as breeding success are influenced by combinations of extrinsic and intrinsic factors. In this study we examined inter‐annual variation and long‐term trends in two aspects of the breeding success of a migratory herbivore, the Bewick's swan Cygnus columbianus bewickii, which is currently undergoing a population decline: 1) the percentage of young within the wintering population and 2) mean brood size. We used an information‐theoretic approach to test how these two measures of productivity were influenced over a 26 yr period by 12 potential explanatory variables, encompassing both environmental (e.g. temperature) and intrinsic (e.g. pair‐bond duration) factors. Swan productivity exhibited sensitivity to both types of explanatory variable. Fewer young were observed on the wintering grounds in years in which the breeding period (May to September) was colder and predator (Arctic fox) abundance was higher. The percentage of young within the wintering population also showed negative density‐dependence. Inter‐annual variance in mean swan brood size was best explained by a model comprised of the negative degree days during the swan breeding period, mean pair‐bond duration of all paired swans (i.e. mean pair duration), and an interaction between these two variables. In particular, mean pair duration had a strong positive effect on mean brood size. However, we found no long‐term directional trend in either measure of breeding success, despite the recent decline in the NW European population. Our results highlight that inter‐annual variability in breeding success is sensitive to the combined effects of both intrinsic and extrinsic factors.     

Extrinsic versus intrinsic factors in the decline and extinction of Australian marsupials

Recent attempts to explain the susceptibility of vertebrates to declines worldwide have largely focused on intrinsic factors such as body size, reproductive potential, ecological specialization, geographical range and phylogenetic longevity. Here, we use a database of 145 Australian marsupial species to test the effects of both intrinsic and extrinsic factors in a multivariate comparative approach. We model five intrinsic (body size, habitat specialization, diet, reproductive rate and range size) and four extrinsic (climate and range overlap with introduced foxes, sheep and rabbits) factors. We use quantitative measures of geographical range contraction as indices of decline. We also develop a new modelling approach of phylogenetically independent contrasts combined with imputation of missing values to deal simultaneously with phylogenetic structuring and missing data. One extrinsic variable-geographical range overlap with sheep-was the only consistent predictor of declines. Habitat specialization was independently but less consistently associated with declines. This suggests that extrinsic factors largely determine interspecific variation in extinction risk among Australian marsupials, and that the intrinsic factors that are consistently associated with extinction risk in other vertebrates are less important in this group. We conclude that recent anthropogenic changes have been profound enough to affect species on a continent-wide scale, regardless of their intrinsic biology.