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Invertebrates dominate many terrestrial ecosystems in terms of biomass, and they also structure ecosystems through their roles as pollinators, detritivores, primary consumers, predators and prey. Invasive rodents (rats and mice) are known to have detrimental effects on many island invertebrates, although these effects are seldom quantified or ecologically understood. Here we provide evidence of the effects of invasive rats ( Rattus spp.) on island invertebrate populations using a large-scale natural experiment. We investigated the effects of invasive rats on Falkland camel crickets ( Parudenus spp.) in the Falkland Islands (South Atlantic) by comparing an index of camel cricket relative abundance between 18 rat-infested islands, six rat-eradicated islands and 13 naturally rat-free islands (in total, 37 islands). Our study provided two key results. First, camel crickets were up to an order of magnitude more abundant on rat-free islands than on rat-infested or rat-eradicated islands. This difference was larger in native tussac grass Poa flabellata than in other vegetation types. Second, camel cricket populations recovered after rat eradication, because the relative abundance of camel crickets on rat-eradicated islands was intermediate between those of naturally rat-free and rat-infested islands, and among rat-eradicated islands relative abundance was lowest where rats had been cleared most recently. Our results demonstrate severe suppression of a superabundant and large-bodied island endemic invertebrate by invasive rodents, and its prompt recovery after rodent eradication. [ABSTRACT FROM AUTHOR]

The Madagascar plover Charadrius thoracicus is a shorebird endemic to western Madagascar, currently classified as globally vulnerable. It is restricted to specialized wetland habitats that are increasingly threatened by humans. To inform future conservation measures for this poorly known species, we develop a predictive habitat suitability map and use this map to estimate the size of the Madagascar plover population. We integrate spatially referenced presence-only observations of Madagascar plovers with Landsat data, elevation data and measures of distance to settlements and the coast to produce a habitat suitability model using ecological niche factor analysis. Validation of this model using a receiver operating characteristic plot suggests that it is at least 84% accurate in predicting suitable sites. We then use our estimate of total area of suitable habitat above a critical suitability threshold and data on Madagascar plover density in suitable sites to estimate the total population size to derive a total population estimate of 3100±396 standard error individuals. Finally, we explore the conservation applications of our model. [ABSTRACT FROM AUTHOR]

Many wildfowl species are declining and 34 out of 159 extant species are globally threatened, some of which are the subject of specific conservation programmes. Here we investigate which factors predict declining population trends across 154 species of Anseriformes. First we show that there are proportionately fewer declining wildfowl populations in North America, Europe and Australasia than in south and central America, Africa and Asia. Second, we use phylogenetic comparative analyses to test whether population size, global range size and ecological, life-history and sexually-selected traits predict population trends. We also consider anthropogenic threats, and human impacts within the breeding and non-breeding ranges of species. Using phylogenetically independent contrasts we show that small population size and small global ranges are the most important intrinsic factors that predispose wildfowl species to declining populations. Many wildfowl are hunted but, contrary to expectation, hunting did not influence population trends. Declining populations were associated with high International Union for the Conservation of Nature (IUCN) threat category, although the relationship is not very strong ( r=0.134, n=129 contrasts) possibly because the IUCN criteria integrate population size, range size and an assessment of threat. Two extrinsic factors were significant predictors of population declines: the increase in area of agricultural land within a species' range (an indirect measure of wetland loss), and the total number of different threat processes such as habitat loss and pollution that threaten a species. Taken together, our results strongly suggest that both anthropogenic threats and intrinsic ecological factors are influencing population declines in wildfowl. [ABSTRACT FROM AUTHOR]

Many shorebirds that breed in North America are declining. These trends reflect global patterns in shorebird populations. Here we ask what factors make some shorebird species more prone to decline than others. Specifically, we test the influence of migratory behaviour (route and distance), biogeography (population size and range), life history (body size, clutch size) and sexual selection (social mating system and testis size) on population trends in North American breeding shorebirds. Using phylogenetic comparative methods, we show that species that migrate across continental North America are more prone to decline than species that do not. Our finding that continental migrants are associated with population decline indicates that intrinsic factors may play an important role in predisposing a species to decline. Previous studies within the class Aves have failed to identify migration route as a correlate of decline or extinction risk. Two other intrinsic factors (oceanic migrants and threats on the non-breeding grounds) were also important in our overall models, although neither was significant alone. The moderate explanatory power of our variables indicates that other factors are also important for explaining shorebird declines. We suggest that contemporary threats, most notably habitat loss and degradation at migratory stopover sites, are likely to be important. [ABSTRACT FROM AUTHOR]

1. Birds with large eyes can achieve a greater pupil diameter and/or focal length, and hence, all other things being equal, greater visual sensitivity and resolution than birds with small eyes. Thus eye size is predicted to reflect adaptations to ecology. 2. We tested three predictions about the relationships between eye size, foraging method (from wholly visual to tactile techniques) and the daily pattern of foraging activity (diurnal/nocturnal) in shorebirds, using phylogenetic comparative methods. 3. We found that shorebirds that forage at night were more likely to have large eyes, but species using vision to detect their prey did not have larger eyes than species that detect their prey by touch. We also found no evidence that nocturnal foragers are more likely than diurnal foragers to use tactile rather than visual cues to detect their prey. 4. These results indicate that evolutionary changes toward nocturnal habits are associated with increases in eye size, and thus with increases in aspects of visual capacity, but that foraging mode may not be the prime selective force in this taxon. [ABSTRACT FROM AUTHOR]

In classical and multi-clutch polyandry, females lay multiple clutches during a breeding season for more than one mate. The production of multiple clutches may be energetically demanding. We used comparative analyses to investigate three possible ways of reducing such egg-laying costs in polyandrous shorebirds: (1) reduction in egg size, (2) reduction in clutch size, and (3) evolutionary increase in female size. Paired comparisons of polyandrous and non-polyandrous taxa showed that females of polyandrous shorebirds lay smaller eggs than females of closely related monogamous and polygynous species. Directional analyses corroborated this result by indicating a significant decrease in egg size after phylogenetically independent origins of polyandry. The comparative analyses uniformly rejected the two alternatives, i.e. neither clutch size nor female size is related to social mating pattern. We also tested and rejected three alternative explanations for reduced egg size in polyandrous taxa. First, we found no evidence that polyandrous females have evolved smaller egg sizes in response to selection to match smaller size of males, which provide the parental care in these species. Second, reduction in egg size was not related to longer breeding seasons (and hence more opportunity for re-nesting). Third, reduced egg sizes were also not related to rates of clutch predation (another potential correlate of multiple clutch production). Our results are thus consistent with the hypothesis that selection for reducing laying costs explains small egg size in socially polyandrous shorebirds. [ABSTRACT FROM AUTHOR]

1. The shape of avian eggs is often explained by involving the mechanical properties of eggshell such as resistance to breakage or invoking physiological forces operating during egg development. 2. Here we take a different approach and investigate the efficient use of space. According to this approach the optimal egg shape is the one that produces the most compact fit under the incubating parent. 3. We extend the model of Andersson (1978) and use a numerical technique to investigate egg shapes in clutches of 1 to 10 eggs. In our model the shape of eggs is described by four parameters in a two-dimensional space. These parameters are free to vary - but eggs cannot be concave. 4. The optimal egg shape for each clutch size was found by a genetic algorithm. 5. The model predicts that egg shape should depend on clutch size. In particular, if the clutch consists of one egg then this egg should be spherical; whereas in clutches of two or three eggs the eggs should be biconical. In clutches of four the eggs should be pointed. The model also predicts that in clutches of over seven eggs the optimal egg shape should be approximately spherical. 6. These predictions are valuable because they point out that some of the variation in avian egg shapes may be explained solely by the efficient use of the brood patch area of the incubating parent. [ABSTRACT FROM AUTHOR]

We studied the clutch-size distribution of Kentish Plover Charadrius alexandrinus in 1991 and 1992 and tested three hypotheses for determination of clutch-size: egg-formation ability of females, incubation ability of parents and nest predation. Variation in clutch-size was small: 71 out of 74 clutches had three eggs (coeff. var. = 7%). Females spent more time foraging (51 ± 6%) pre-laying and during egg-laying than their mates (39 ± 5%). However, we concluded that egg-formation was not constrained by food availability because 77% and 100% of clutches were initiated before the peaks of prey density and of prey mass, respectively. Furthermore, the number of clutches initiated and completed over time was unrelated to prey density. By experimentally reducing and enlarging clutches, we found that enlarged clutches of four eggs took longer to hatch (24.8 ± 0.9 days) than control clutches of three (21.6 ± 0.7 days). Eggs of enlarged clutches also lost weight more slowly during incubation in both years compared with control clutches. No difference was found in the incubation behaviour or weight loss of parents between reduced, control and enlarged clutches. We found no evidence to support the nest predation hypothesis, since neither the proportion of nests predated nor the number of chicks hatched was different between reduced, control and enlarged clutches. The results of this study are most consistent with the incubation ability hypothesis, although the parental ability hypothesis has remained untested. [ABSTRACT FROM AUTHOR]