Peter Arcese

Are Integrated Conservation-Development Projects (ICDPs) Sustainable? On the conservation of large mammals in sub-Saharan Africa

Abstract Initiatives to link rural development and species conservation, known as integrated conservation-development projects (ICDPs), have been launched with considerable fanfare and funding around the world. Although ICDPs hold appeal as broader ecological efforts than the conservation and development strategies that preceded them, they also suffer conceptual flaws that may limit their appropriateness and potential sustainability, at least when applied to the protection of large African mammals.

Human demography and reserve size predict wildlife extinction in West Africa

Species - area models have become the primary tool used to predict baseline extinction rates for species in isolated habitats, and have influenced conservation and land-use planning worldwide. In particular, these models have been used to predict extinction rates following the loss or fragmentation of natural habitats in the absence of direct human influence on species persistence. Thus, where direct human influences, such as hunting, put added pressure on species in remnant habitat patches, we should expect to observe extinction rates higher than those predicted by simple species - area models. Here, we show that extinction rates for 41 species of large mammals in six nature reserves in West Africa are 14-307 times higher than those predicted by models based on reserve size alone. Human population and reserve size accounted for 98% of the observed variation in extinction rates between reserves. Extinction occurred at higher rates than predicted by species-area models for carnivores, primates and ungulates, and at the highest rates overall near reserve borders. Our results indicate that, where the harvest of wildlife is common, conservation plans should focus on increasing the size of reserves and reducing the rate of hunting.

Optimal conservation of migratory species.

Background Migratory animals comprise a significant portion of biodiversity worldwide with annual investment for their conservation exceeding several billion dollars. Designing effective conservation plans presents enormous challenges. Migratory species are influenced by multiple events across land and sea–regions that are often separated by thousands of kilometres and span international borders. To date, conservation strategies for migratory species fail to take into account how migratory animals are spatially connected between different periods of the annual cycle (i.e. migratory connectivity) bringing into question the utility and efficiency of current conservation efforts. Methodology/Principal Findings Here, we report the first framework for determining an optimal conservation strategy for a migratory species. Employing a decision theoretic approach using dynamic optimization, we address the problem of how to allocate resources for habitat conservation for a Neotropical-Nearctic migratory bird, the American redstart Setophaga ruticilla, whose winter habitat is under threat. Our first conservation strategy used the acquisition of winter habitat based on land cost, relative bird density, and the rate of habitat loss to maximize the abundance of birds on the wintering grounds. Our second strategy maximized bird abundance across the entire range of the species by adding the constraint of maintaining a minimum percentage of birds within each breeding region in North America using information on migratory connectivity as estimated from stable-hydrogen isotopes in feathers. We show that failure to take into account migratory connectivity may doom some regional populations to extinction, whereas including information on migratory connectivity results in the protection of the species across its entire range. Conclusions/Significance We demonstrate that conservation strategies for migratory animals depend critically upon two factors: knowledge of migratory connectivity and the correct statement of the conservation problem. Our framework can be used to identify efficient conservation strategies for migratory taxa worldwide, including insects, birds, mammals, and marine organisms.

Immigration and the ephemerality of a natural population bottleneck: evidence from molecular markers

Population bottlenecks are often invoked to explain low levels of genetic variation in natural populations, yet few studies have documented the direct genetic consequences of known bottlenecks in the wild. Empirical studies of natural population bottlenecks are therefore needed, because key assumptions of theoretical and laboratory studies of bottlenecks may not hold in the wild. Here we present microsatellite data from a severe bottleneck (95% mortality) in an insular population of song sparrows (Melospiza melodia). The major findings of our study are as follows: (i) The bottleneck reduced heterozygosity and allelic diversity nearly to neutral expectations, despite non–random survival of birds with respect to inbreeding and wing length. (ii) All measures of genetic diversity regained pre–bottleneck levels within two to three years of the crash. This rapid recovery was due to low levels of immigration. (iii) The rapid recovery occurred despite a coincident, strong increase in average inbreeding. These results show that immigration at levels that are hard to measure in most field studies can lead to qualitatively very different genetic outcomes from those expected from mutations only. We suggest that future theoretical and empirical work on bottlenecks and metapopulations should address the impact of immigration.

Effective enforcement in a conservation area.

Wildlife within protected areas is under increasing threat from bushmeat and illegal trophy trades, and many argue that enforcement within protected areas is not sufficient to protect wildlife. We examined 50 years of records from Serengeti National Park in Tanzania and calculated the history of illegal harvest and enforcement by park authorities. We show that a precipitous decline in enforcement in 1977 resulted in a large increase in poaching and decline of many species. Conversely, expanded budgets and antipoaching patrols since the mid-1980s have greatly reduced poaching and allowed populations of buffalo, elephants, and rhinoceros to rebuild.

Stability, regulation, and the determination of abundance in an insular song sparrow population

The population dynamics of the Song Sparrow, Melospiza melodia, were studied for 15 yr on Mandarte Island, in southwestern British Columbia, Canada. This population exhibited a high median density (7.8 females/ha) and fluctuated strongly (10—fold or more) from year to year. The population received few successful immigrants, even at low densities, and its dynamics were thus driven by local events. Two strong density—dependent regulating mechanisms were detected. First, reproductive output was strongly depressed at high densities because of an increased rate of nest failure and a decline in mean clutch size. Greater nest failure at high density was due to increased predation on eggs and nestlings. Nest failure increased with the rate of nest parasitism by Brown—headed Cowbirds (Molothrus ater) and was lowest when cowbirds were absent from Mandarte, suggesting that cowbirds either cause or facilitate nest failure. Second, the rate of juvenile recruitment was inversely related to the density of adults, becaus...

Intrasexual competition, mating system and natal dispersal in song sparrows

Abstract This study examines relationships between natal dispersal and intrasexual competition, the mating system, inbreeding, inheritance and social status in five cohorts of song sparrows, Melospiza melodia, resident on Mandarte Island, B.C., Canada. The role of natal dispersal in population regulation is also considered. Several hypotheses of natal dispersal were tested with experimental and observational data. Dispersal distances were similar among the sexes, but distances depended strongly on point of origin on the island. Adding supplemental food on 15 territories dramatically reduced dispersal distance in each sex relative to controls, supporting the hypothesis that dispersal results from intrasexual competition for access to high-quality breeding territories. No evidence for genetic determination of dispersal distance, or for mechanisms that serve to prevent close inbreeding, was found. Social status was related to the time of settlement, but not to distance dispersed on Mandarte. Subordinate birds emigrated from Mandarte more often than dominants. Dispersal distance on Mandarte was unrelated to the probability of settling with a relative, but neither distance moved nor relatedness of the first mate were related to lifetime reproductive success. Disappearance of juveniles coincided with periods of territoriality in late summer through autumn and late winter through spring. The proportion of juveniles recruiting to the population declined as the number of territorial adults in the autumn increased. These results suggest a close link between intrasexual competition for breeding territories, natal dispersal and population regulation.

Inbreeding depresses immune response in song sparrows (Melospiza melodia): direct and inter–generational effects

A thorough knowledge of relationships between host genotype and immunity to parasitic infection is required to understand parasite–mediated mechanisms of genetic and population change. It has been suggested that immunity may decline with inbreeding. However, the relationship between inbreeding level and a hosts response to a novel immune challenge has not been investigated in a natural population. We used the pedigreed population of song sparrows (Melospiza melodia) inhabiting Mandarte Island, Canada, to test the hypothesis that a sparrows cell–mediated immune response (CMI) to an experimental challenge would decline with individual or parental inbreeding. CMI in 6–day–old chicks declined significantly with their mothers coefficient of inbreeding, demonstrating an inter–generational effect of maternal inbreeding on offspring immunity. In fledged juveniles and adult sparrows, CMI declined markedly with an individuals own coefficient of inbreeding, but not its mothers. This relationship was consistent across seasons, and was not attributable solely to heterosis in offspring of immigrant breeders. CMI also declined with age and increased with body condition in adult sparrows, but inbreeding explained 37% of the total variation. We emphasize the implications of this dramatic inbreeding depression in cell–mediated immunity for theories of parasite–mediated evolution and the susceptibility of small, inbred populations.

Repertoire size, territory acquisition and reproductive success in the song sparrow

Abstract Song repertoire size, time to first territory acquisition, territory size, territory tenure and lifetime reproductive success were measured in males of known age in a wild, resident population of song sparrows, Melospiza melodia. One-year-old males had smaller repertoires than older males, but this apparent change in repertoire size was due to attrition of individuals with small repertoires rather than to an increase in the repertoire size of individuals with age. Males with large repertoires held territories longer and had greater annual and lifetime reproductive success than males with small repertoires. Half-hour repertoire size, which may represent an ecologically more relevant measure of repertoire size perceived by a transient listener, was also positively related to territory tenure and annual reproductive success. Thus listeners might be able to assess a singing males competitive ability without sampling the entire repertoire.

Age, intrusion pressure and defence against floaters by territorial male song sparrows

Abstract Possession of a territory is essential to successful reproduction in male song sparrows, Melospiza melodia. However, the aggressive behaviour of territory owners frequently prevents some males from settling. Several factors that might affect the ability of territory owners to defend their territories against intrusion by non-territorial ‘floater’ males were investigated. Floaters lived secretively on the territories of owners, but were only occasionally detected by them. During consecutive breeding seasons, intrusions were most frequently observed on the territories of birds older or younger than 2 or 3 years. As males aged, intrusion pressure on their territories changed as predicted by patterns observed within seasons. Males experienced similar intrusion pressure in each year with respect to the means of their age classes. However, intrusion pressure on the same territory was not correlated across years, nor across different owners of a territory within years. Intrusion pressure was therefore an attribute of males rather than of territories. Males that experienced high intrusion pressure held territories for shorter periods, and they sometimes possessed handicaps that decreased their ability to evict floaters. Two-and 3-year-old males held their territories longest. Intrusion pressure was unrelated to floater density, territory size, to whether a female was present on the territory, or to the fertility of territorial females. This study shows that floaters intrude selectively against particular males, and that the ability to defend a territory against floaters first increases and then decreases with age in male song sparrows.