Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya

Competition and compatibility between livestock and wildlife in Africa has been a point of considerable speculation, with implications for conservation. However, controlled replicated experiments are lacking. Here we report on the results of a long-term exclosure experiment in Laikipia, Kenya, in which different guilds of large mammalian herbivores have been independently manipulated since 1995. In plots from which cattle were excluded, the density of zebra dung in 2000 was on average 46% greater than in control plots. This was due to differential zebra use, and not to differential rates of dung removal (by dung beetles or other factors). Vegetation data indicate that cattle fully compensate for the absence of wildlife; all plots accessible to cattle had similarly low grass cover. However, wildlife do not fully compensate for the absence of cattle; plots with only wildlife had more grass cover than plots accessible to cattle. Zebra dung density was strongly correlated with total grass cover, suggesting that zebras are effectively tracking resource abundance. There is also evidence of pair-wise competition between cattle and elephants, and between elephants and zebras. The strong competition between cattle and zebras appears to be mitigated by the presence of elephants. A significant cattle x elephant interaction on the abundance of zebra dung indicates that elephants reduce the negative effects of cattle on zebras. In the presence of cattle, elephants facilitate the abundance of zebra, apparently by suppressing resource extraction (bite rates) by cattle. The precise mechanism for this indirect facilitation is not clear, but it may be related to the demonstrated reduction in forb cover associated with elephant presence.     

Habitat management and patterns of predation of Northern Lapwings on wet grasslands: The influence of linear habitat structures at different spatial scales

In managed landscapes, habitat structure is frequently manipulated through the creation of features such as tracks, hedges, and waterways. If predator and prey activity are concentrated around these features, levels of predation may be elevated in these landscapes. This issue is of particular importance when habitat structures are used to attract species of conservation concern. For example, the installation of linear waterways in wet grasslands is a common form of habitat management to benefit breeding waders and wader nests and foraging chicks tend to be aggregated around wet features. If predator activity is also focused around these features, and if their linearity increases the probability of prey being located, then the conservation benefits of this management technique may be eliminated. We explore predator movement in relation to the structure and complexity of linear wet features within a lowland wet grassland landscape. We examine patterns of nest and chick predation in lapwing (Vanellus vanellus) at the whole-site, between-field and within-field scales. Mammalian predators were responsible for the majority of nest predation. However, we found no evidence that mammalian predators used linear wet features disproportionately within the landscape, or that wet feature distribution influenced the probability of nest or chick predation. At the whole-site scale, nest predation rates were significantly higher in areas with greater predator presence and lowest where the number of breeding neighbours was high. Thus, predation levels were influenced by large-scale patterns of predator presence and lapwing density but not by the use of linear wet features as a habitat management tool. Managing predator impacts is therefore likely to require empirical assessments of local predator distribution and abundance in order to target measures effectively.     

Savanna herbivore dynamics in a livestock-dominated landscape: I. Dependence on land use, rainfall, density, and time

Ecosystem processes in African savannas can be better conserved if management is based on a mechanistic understanding of wildlife dynamics in livestock-dominated landscapes. For Laikipia District, a non-protected savanna region in northern Kenya, we used spatially explicit estimates of density to characterize factors influencing the dynamics of large herbivores on three land-use types: commercial ranches that favor wildlife, communal ‘group ranches’ practicing pastoralism, and the remainder (‘transitional’ properties). For 21-year time series of nine wild and two domestic species, linear model selection was used to ascribe between 45% (Grant’s gazelle) and 95% (plains zebra) of observed variation in biomass density to land use, rainfall-dependence, density-dependence, and trends over time.Strongly opposing patterns of variation across the landscape in wildlife and livestock densities affirmed the primacy of land use among factors influencing wildlife abundance in non-protected areas. Rainfall limited densities of only the dominant grazing species throughout the monitoring period (plains zebra and cattle), and of most other species while their densities were high. Regulating effects of density were detected only for the dominant wild grazing and browsing species (zebra and giraffe). All but two wild species (zebra and Grant’s gazelle) declined on at least one land-use type, for reasons that varied among land uses.Where favored, diverse and abundant wild herbivores (mean of 1.7 t km⁻² on pro-wildlife ranches) can thrive even when sharing the landscape with a slightly higher biomass density of livestock (mean of 2.7 t km⁻²). Where not favored, only a few resilient wild species (e.g. gazelles and plains zebra) persist with high densities of livestock (mean of 4.6 t km⁻² on transitional ranches). Maintaining higher wild species diversity in the landscape will depend on the creation of a network of unfenced conservation areas in which livestock densities are persistently low or zero, which are sufficiently large to act as ‘sources’ of wild species that are prone to displacement by humans and livestock, and which generate benefits to community members that exceed opportunity costs.     

Empty forests: Large carnivore and prey abundance in Namdapha National Park, north-east India

Illegal hunting poses a dual threat to large carnivores through direct removal of individuals and by prey depletion. We conducted a camera-trapping survey in the Namdapha National Park, north-east India, conducted as part of a programme to evaluate carnivore and prey species abundance. Clouded leopard (Neofelis nebulosa) was the only large carnivore detected by camera-trapping. Indirect evidences indicated the presence of the wild dog (Cuon alpinus) and leopard (Panthera pardus), however, there was no evidence of tigers (Panthera tigris), suggesting their possible extinction from the lower elevation forests. Of the major ungulate prey species, sambar (Cervus unicolor) and wild pig (Sus scrofa) were the only large prey detected, while the Indian muntjac (Muntiacus muntjak) was the only small prey species detected. Relative abundances of all species were appreciably lower than estimates from other tropical forests in south-east Asia. We suspect that illegal hunting may be the cause for the low carnivore and prey species abundance. An ongoing community-based conservation programme presents an opportunity to reduce local people’s dependence on hunting by addressing their socio-economic needs and for using their skills and knowledge of the landscape for wildlife conservation. However, long-term wildlife monitoring is essential to assess the efficacy of the socio-economic interventions in bringing about wildlife recovery.     

Resolving the urban nest predator paradox: The role of alternative foods for nest predators

Urbanization is a leading cause of species endangerment in the United States; however, certain species thrive in urban habitats. The loss of key predators or the addition of new predators in urban areas could alter the structure of urban communities. A reduction in nest predation is hypothesized to explain the high density of urban birds, yet urban areas typically have increased populations of avian nest predators. The loss of important nest predators in urban habitats, prey switching of urban predators, or successful nest defense against avian nest predators could explain this urban nest predator paradox. To assess these hypotheses I compared nest predation rates of Northern mockingbirds (Mimus polyglottos) in parking lots and residential neighborhoods to populations in pastures and wildlife preserves during 2007–2009 in Florida, USA and placed video cameras on a subset of nests in 2008–2009. Data do not support the hypothesis that urban nest predation rates are consistently lower than non-urban nest predation rates. Of the 56 nest predation events recorded, cats were the dominant urban predator and Cooper’s hawks (Accipiter cooperii) were the dominant non-urban predator. There was no evidence for a loss of important nest predators in urban habitats; however, prey switching by Cooper’s hawks likely occurred. There was also indirect evidence for the importance of nest defense. Furthermore, some of the cats recorded as nest predators in residential neighborhoods were owned cats and all but one cat predation event occurred at night. To reduce nest predation rates, cat owners should keep their cats indoors at night.     

Predator-prey relationships and responses of ungulates and their predators to the establishment of protected areas: A case study of tigers, leopards and their prey in Bardia National Park, Nepal

Interactions among sympatric large predators and their prey and how they respond to conservation measures are poorly known. This study examines predictions concerning the effects of establishing a protected area in Nepal on tigers (Panthera tigris), leopards (Panthera pardus), and their ungulate prey. Within a part of the park, after 22 years the total density of wild ungulates had increased fourfold, to ca. 200 animals/km², almost exclusively due to a remarkable increase in chital deer (Axis axis). Tiger density also increased markedly to nearly 20 animals/100 km², whereas leopard density did not and was ca. 5 animals/100 km². The prediction that grazers should increase more than browsers was only partially supported. The prediction of positive density dependence in prey selection was not supported. Instead, the most abundant species (chital and hog deer, Axis porcinus) were killed less frequently than expected, whereas the lower-density wild boar (Sus scrofa) was preferred. Predictions that (i) initially rare species suffer highest predation was partially supported, that (ii) predation is highest among the most abundant prey was not supported, and that (iii) predation is highest among the most preferred prey independently of their densities was supported. Clearly, the conservation efforts adopted in Bardia were successful, as both tigers and their natural prey base increased. However, the positive numerical response of tigers limited and depressed the abundance of some prey species. Thus, conservation activities aimed at restoring large predators are likely to change in the composition of the overall mammal community, potentially eliminating rare but preferred prey species.     

Implications of intraguild predation for sea turtle nest protection

In the United States, raccoons Procyon lotor are often removed from sea turtle nesting beaches to decrease egg mortality. However, raccoons also consume ghost crabs Ocypode quadrata, another common egg predator. Reducing predator populations can benefit secondary predators, inflating total predation pressure and leading to a decline in prey species. We used track and burrow counts to compare raccoon and ghost crab abundance at four beaches in Florida, USA, that differ in management activity and determined predation rates on loggerhead Caretta caretta nests by each predator. Mean raccoon abundance (range 0.12-0.46 tracks plot⁻¹ night⁻¹) and ghost crab density (0.09-0.19 burrows m⁻²) were inversely correlated. Ghost crabs were largest at the site with the fewest raccoons. The stable nitrogen isotope ratios of ghost crabs (mean 9.8‰) were positively correlated with body mass, indicating larger ghost crabs feed at a higher trophic level and suggesting large ghost crabs may consume more loggerhead eggs. The highest rates of egg predation by both predators (31%) occurred where raccoon abundance was lowest and ghost crab abundance was highest, suggesting ghost crab burrows may facilitate predation by raccoons. Our data suggest that predation by raccoons limits ghost crabs and that removing raccoons can increase ghost crab abundance and sea turtle egg mortality. Although predator removal can be effective when nest predation rates are quite high, maintaining moderate raccoon densities may be important for controlling ghost crabs. These results highlight the importance of understanding food web connectivity in developing management strategies to achieve conservation goals, especially when the species of concern are threatened or facing extinction.     

Conserving the benefits of predator biodiversity

Organisms at higher trophic levels often face a disproportionate risk of local or regional extinction, while at the same time many ecosystems are being invaded by non-native predators. Global environmental change fosters both processes, further altering predator biodiversity. Thus, there has been growing interest in how predator species richness impacts ecosystem functioning. Manipulative experiments have revealed that complementarity and sampling effects, two mechanisms commonly found to underlie diversity effects at other trophic levels, also commonly impact the relationship between predator diversity and prey suppression. Intraguild predation and non-consumptive (behaviorally-mediated) effects on prey, two mechanisms without direct analogs among plants, also strongly impact predator-diversity effects. Predator diversity studies are particularly relevant to conservation because they focus on the trophic group that is most prone to extinction, and because they nearly always measure diversity effects that span several trophic levels. Predator invasions may partly offset species-richness losses to extinction, but because invasive predators typically reach much higher densities and exert stronger impacts on prey than do native species, and because they also displace ecologically-similar native predators, invasion is likely to disrupt natural predator function. A framework for predicting which predator-diversity mechanisms are likely to operate in a given community, and experiments that span more realistic spatiotemporal scales and include large vertebrate predators, are needed to improve the relevance of predator-diversity experiments to conservation decision-making in the future.     

Do wildlife passages act as prey-traps?

A number of studies have proposed that wildlife passages beneath roads and railway lines might be exploited by mammalian predators as ‘prey-traps’ with prey-species being effectively funnelled into areas of high concentration. This proposition has raised the possibility that use of passages by predators may reduce the effectiveness of passages in conserving other forms of wildlife. We review the literature and conclude that evidence for the existence of prey-traps is scant, largely anecdotal and tends to indicate infrequent opportunism rather than the establishment of patterns of recurring predation. Most passage studies record no evidence of predation in or around passages. Conversely, there is some evidence that predator species use different passages than their prey.     

A conservation success story in the otherwise dire megafauna extinction crisis: The Asiatic lion (Panthera leo persica) of Gir forest

Carnivores in Asia and throughout the world face high risk of extinction due to factors such as continued habitat loss and hunting. However, the Asiatic lion of Gir forest, India presents a conservation success story whose history may help to guide the recovery and conservation of other imperiled predators. Protection of core and satellite habitats and the relocation of pastoral communities and their livestock triggered forest recovery and coincident increases in native prey populations. Wild ungulate populations increased by 10-fold between 1970 and 2010, supporting an increase in the lion population from 180 animals in 1974 to 411 animals in 2010. Coincident with this increase, lions shifted their predation preferences from a diet composed of 75% livestock to one composed of just 25% livestock. This example demonstrates the value of native prey populations to sustain imperiled carnivore species, and the use of protected areas and livestock exclusion to maintain healthy prey populations.     

Population decline of tsessebe antelope (Damaliscus lunatus lunatus) on a mixed cattle and wildlife ranch in Zimbabwe

The estimated number of tsessebes on a cattle and wildlife ranch in Zimbabwe decreased during 1995-1999 from 2209 to 435 animals. Existing records of rainfall, cattle management, wildlife numbers, captures, hunting and predation were analysed and, together with a demographic model and limited fieldwork, used to identify the probable cause of this decline. There was no convincing evidence that cheetah predation, excessive legal or illegal offtakes, a food shortage as a direct consequence of the 1994/1995 drought, or interspecific competition with wild herbivores were likely causes. After the 1991/1992 drought, tsessebe number was negatively correlated with cattle biomass, suggesting that cattle and tsessebe have competed for food since then. Two factors probably caused a long-lasting reduction in the dry-season availability of green grass leaf (the preferred food of tsessebe). First, drought and heavy grazing pressure by cattle may have shifted sward composition away from leafy grasses and towards grass species with small, wiry leaves. Secondly, while shrub encroachment has been occurring for decades, the 1991/1992 drought probably encouraged the establishment of another cohort of bushes, which now compete with grasses for soil moisture, reducing the water available for grass growth during the dry season. The competition between tsessebe and cattle was masked by significant cattle destocking during 1992-1995, but became apparent after 1995 when cattle numbers were increased. This competition was exaggerated by a general decline, since 1994, in rainfall during September-October, which further reduced the late dry season supply of green grass.     

Herbivory, hunting, and long-term vegetation change in degraded savanna

Large ungulate populations are associated with the degradation of many forest plant communities, but it is unclear if these population sizes are strictly a contemporary phenomenon. Human exploitation models predict they are not, with ungulate numbers varying with long-term fluctuations in hunting pressure. Alternatively, human disturbance models predict that abiotic limitations normally restrict herbivores, with contemporary increases reflecting increased productivity associated with agriculture and forestry. Both can explain ungulate abundance, but may have different implications for plant conservation because they predict different levels of prior evolutionary exposure to herbivory. Here, I review historical records and stand structure studies from degraded oak savanna of western North America to examine whether current ungulate levels are strictly a contemporary phenomenon. Although it was impossible to quantify pre-European herd sizes, all evidence indicates a strong relationship between hunting pressure and ungulate abundance. Historical accounts repeatedly describe large herds of deer and elk at first European contact, followed by sharp declines immediately after colonization, and then rapid recovery beginning in the early 1900s as subsistence hunting waned. Stand structure data for oak woodland appear to support this model. Present-day oak woodlands mostly derive from mass recruitment from 1850 to 1910, coinciding with the near elimination of ungulates by hunting. Although these results suggest that large ungulate herds are not strictly a contemporary phenomenon, browsing intensity appears to be unprecedented given limited hunting, predator extirpation, and savanna fragmentation within productive pasture and early successional forest. Hunting pressure thus continues to be important, in that it is now largely absent.     

The red fox in Australia—an exotic predator turned biocontrol agent

The most important problem regarding mammal conservation in mainland Australia is the low abundance and limited distributions of many species, a legacy of an unprecedented collapse of the mammal fauna on a continental scale that unfolded following European colonisation. Two major hypotheses (not necessarily always mutually exclusive) have been proposed to account for the collapse (1) niche loss-damage due to a variety of causes and (2) predation by exotics, in particular by the red fox. This paper provides evidence the supporting the latter cause as a major factor.Five case studies in Western Australia demonstrate that the fox is an efficient predator that restricts medium-sized marsupials to refugia at low densities. Removal of the fox by baiting typically produces two prey responses (1) significant population recoveries and (2) the colonisation and exploitation of habitats outside of refugia. To date, 11 medium-sized marsupial species, representing seven families, have responded in a like manner. The impact of the fox on its known marsupial prey mimics a biocontrol agent as it severely limits prey distribution and abundance. Niche denial and population suppression characterise it's actions on a suite of vulnerable species not yet fully documented.     

Conservation of the dark-rumped petrel Pterodroma phaeopygia in the Galapagos Islands,Ecuador

The effects of predation and habitat deterioration produced by rats, cats, dogs, pigs, goats, burros and cattle, which have been introduced over the last two centuries to the Galapagos archipelago, have reduced the dark-rumped petrel Pterodroma phaeopygia population so that it is now in danger of extinction. By controlling rat numbers through poisoning, and by protecting the nesting colony from other predator and pest species through hunting, petrel breeding success in the Cerro Pajas colony, Floreana Island, has been increased. Preliminary studies indicate that immediate conservation efforts are also needed and are being initiated for at least two other petrel populations. Continued predator control is essential to halt further petrel population declines and to allow their numbers to recuperate.     

Underestimated and severe: Small mammal decline from the forests of south-eastern Australia since European settlement, as revealed by a top-order predator

In Australia, numerous small mammal species have suffered extinction or severe declines in distribution and abundance following European settlement. The extent of these declines from forested areas of south-eastern Australia, however, remains poorly understood. In this paper we use sub-fossil deposits of the sooty owl (Tyto tenebricosa tenebricosa) as a tool for understanding the diversity of the small mammal palaeocommunity. These results are compared to the contemporary sooty owl diet from the same geographical region to investigate the degree of small mammal decline following European settlement.Of 28 mammal species detected in sub-fossil deposits and considered prey items of the sooty owl at the time of European settlement, only 10 species were detected in the contemporary sooty owl diet. Numerous small mammal species have not only recently suffered severe declines in distribution and abundance but have also recently undergone niche contraction, as they occupied a greater diversity of regions and habitats at the time of European settlement. For some species our understanding of their true ecological niche and ecological potential is therefore limited. The species that underwent the greatest declines occupied open habitat types or were terrestrial. The severity of decline is also likely to have resulted in severe disruption of ecosystem functions, with wide scale ecosystem consequences. There is an urgent need to improve small mammal conservation, to maintain crucial ecosystem functions performed by small mammals. It is recommended that broad-scale exotic predator control programs are conducted which may also provide suitable conditions for the re-introduction of locally extinct species.     

Free-ranging domestic dogs (Canis familiaris) as predators and prey in rural Zimbabwe: threats of competition and disease to large wild carnivores

Domestic dogs (Canis familiaris) arrived in Zimbabwe ca. 1000 years ago. Numbers of free-ranging dogs have reached unprecedented levels in communal lands (agro-pastoralist rural areas), and interact with large wild carnivores along boundaries with wildlife reserves as predators and prey. This study examined a population of 236 dogs in a 33-km² section of Gokwe Communal Land (GCL) bordering the Sengwa Wildlife Research Area (SWRA) in north-western Zimbabwe in 1995-1996. Dogs were found up to 6 km within the SWRA, and were the most common carnivore on the GCL-SWRA boundary. Observations of 16 radio-collared dogs showed that they were inefficient predators. Only 20 kills were recorded amongst the remaining dog population, of which three were wild ungulates. Dogs were unsuccessful predators due to their small group size (mean 1.7) and body mass (mean 14.7 kg), and the abundance of alternative food. It is therefore unlikely that they compete with large carnivores for wild prey. However, leopards (Panthera pardus), lions (P. leo) and spotted hyaenas (Crocuta crocuta) preyed on dogs in GCL, removing ?6% of the dog population in 1993. Such predation provides ideal circumstances for disease transmission. Canid disease was prevalent in the study area; including rabies and probably distemper. The risk of infection is greatest during the dry season (May-October), when peaks in rates of disease, carnivore incursions into GCL, and predation on dogs coincided. The role of jackals (Canis adustus and Canis mesomelas) and spotted hyaena predation of dogs is discussed in relation to disease epidemics within wildlife reserves. With a dog population growth rate of 6.5% per annum, and the prevalence of canid diseases, the conservation threat posed by dogs is escalating on communal land-wildlife reserve boundaries in Zimbabwe. Measures to control dog numbers and improve vaccination coverage of dogs are discussed.     

Is nest predator exclusion an effective strategy for enhancing bird populations?

Evidence suggests that nest predation is a serious problem for the conservation of bird populations. Managers are, therefore, faced with decisions of whether to intervene to reduce this impact and if so what interventions to use. Nest predator exclusion is one of the most widely used methods for reducing predation, particularly for ground-nesting species, but studies testing its effectiveness have shown mixed results. We used explicit systematic review methodology to determine the impact of nest predator exclusion on hatching success. We used meta-analysis to summarise results from 16 predator exclusion studies. We also investigated whether factors relating to characteristics of the prey, predator species, location and study methodology explained heterogeneity in effect sizes. Predator exclusion using either exclusion fences or nest-cages resulted in a significant increase in hatching success. This was the case for declining as well as increasing bird populations indicating that nest predator exclusion is an effective method of increasing hatching success of vulnerable species. Nest-cages had a larger effect on hatching success than exclusion fences, although this difference was not significant and additional nest-cage studies are required as sample sizes were small. Heterogeneity in effect sizes was not explained by any of the covariates investigated. Studies have shown that nest-cages can lead to increased levels of predation on incubating adults and so should be used with caution especially within small populations. Research is required to determine whether increased hatching success following nest predator exclusion results in increased breeding populations as improving hatching success alone does not ensure improved conservation status of bird populations.     

Earthworm primers for DNA-based gut content analysis and their cross-reactivity in a multi-species system

Specific primers can be used in polymerase chain reactions (PCR) to amplify prey DNA from the gut content of generalist predators at high specificity and sensitivity. A prerequisite for applying this approach to field studies, however, is to confirm that primers are actually targeting specific prey species or prey groups and do not produce false positive results by amplifying DNA either from predator species or from the wide range of potential alternative prey found under natural conditions. Here, we report on a new group-specific primer pair for earthworms designed from cytochrome oxidase c subunit 1 (COI) sequences of 11 earthworm species found in Central Europe that can be used to detect consumption of earthworms by invertebrate predators. Besides inter-specific also considerable intra-specific variation was found for COI sequences among most of the earthworm species. We, therefore, combined a universal forward primer with an earthworm-specific reverse primer which amplified a 523 bp product from all 11 species tested. Earthworm DNA amplification was also successful in the presence of excess DNA of a predator species. The primer pair was tested against 82 non-target invertebrate species commonly found in the same habitats, including potential prey for generalist predators and predators themselves. The earthworm primer was highly specific: only one of the non-target species showed a product of similar length as the earthworms, whereas PCR with 12 non-target species produced amplicons whose length differed from that of earthworms. We conclude that the new primer will be a useful tool to investigate the role earthworms play as a food resource in soil food-webs. Moreover, we suggest that future studies utilizing DNA-based approaches for prey detection should select non-target species for cross-reactivity tests according to their abundance and importance rather than choosing representatives of taxonomic units; this will help validate the results achieved using species- or group-specific primers and guarantee their meaningful ecological interpretation.     

Population viability and species interactions: Life outside the single-species vacuum

Population viability analysis (PVA) has become a widely used set of tools for evaluating relative extinction risk and prioritizing management options among imperiled populations. While PVA is a widely sanctioned tool in conservation biology, the field of population viability is in its infancy with respect to species interactions. In this paper, I review available methods for evaluating extinction risk when species interactions contribute significantly to population viability. This review includes an evaluation of six broad categories of species interactions (predation, disease, competition, mutualism, parasitism and host-parasitoid interactions) in population viability analysis, with a particular focus on predation as a case study. I first evaluated how often species interactions are considered when PVA is applied to population data from imperiled species. I identified 378 articles in commonly cited conservation journals, of which 24 attempted a viability analysis for populations threatened by interactions with other species. Most of these PVA’s treat a putative species interaction as a constant source of mortality rather than a coupled, dynamic population process. Second, I reviewed the literature to identify the availability of time-series of abundance data for two interacting species in which at least one species was threatened or endangered. Adequate time-series data were available for both species comprising an interacting pair in only 9 out of 407 papers reviewed. Third, I used a stochastic, fully stage-structured predator prey model to create time-series data (vital rates and projection matrices) in order to quantify the efficacy of two matrix-based, single-species PVA approaches. Simple single-species PVAs confound stochastic variation with population cycles induced by species interactions (in this case predation). As a result these models provide conservatively biased forecasts of viability. Unfortunately, the data needed to construct more complex PVA’s with feedback and multi-species stochasticity are rarely collected. I close with a discussion of key advances needed to “escape the population vacuum” in a move toward more realistic estimates of extinction risk.     

Wader nest distribution and predation in relation to man-made structures on coastal pastures

Coastal pastures and other wet grasslands are important but decreasing breeding habitats for many waders (Charadrii). Since loss of suitable habitat is a major reason for population declines, protection and restoration of these habitats is crucial. Reduction of the often high rate of nest predation is a potentially important tool in future conservation work. Here, we focus on predators’ use of raised structures in the landscape when searching for prey. Hooded crows (Corvus corone cornix) use man-made structures such as stone walls and barbed wire fences when foraging on coastal pastures in SW Sweden. However, few studies have examined wader breeding success in relation to man-made structures, and the extent to which such structures are used by searching nest predators. We measured the spatial distribution and rate of predation on wader nests in relation to such structures. Crows spent more time at or near man-made structures than expected by chance, but we found no significant difference in nest predation relative to distance from man-made structures. However, wader nests were placed farther away from man-made structures than expected by chance in two out of three years. Waders thus tend to avoid breeding close to man-made structures, which therefore reduce the suitable breeding area and probably also the local wader population size.