Environmental change, extinction and human activity: evidence from caves in NW Madagascar

In the last 2000 years, changes on the island of Madagascar have resulted in the modification of key environments and the extinction of nearly all large native animals. Humans have long been suspected as the primary cause of this ecological catastrophe, but the exact mechanisms of the island's rapid transformation and the role of natural factors such as climate change remain uncertain. Caves in northwestern Madagascar are helping researchers to disentangle these factors, by providing many types of datable information concerning the past in close physical proximity. U -series dated pollen spectra from the caverns of Anjohibe provide a 40,000-year record of vegetation in the vicinity. Bone deposits from caves in the region provide new site records for extinct taxa, including Babakotia radofilai Godfrey et al . 1990, Plesiorycteropus madagascariensis Filhol 1895, and Mullerornis sp. Several extant taxa that were present in the region in the late Holocene are now locally extinct. Archaeological evidence from the caves suggests little or no human activity in the vicinity or interaction with the fauna at these sites until recent centuries.     

Social Influences on Group Membership in <Emphasis Type="Italic">Propithecus verreauxi verreauxi</Emphasis>

The size and composition of a social group can influence the reproductive success of its members. I examined the hypothesis that residents actively try to manipulate group size and composition in Verreaux’s sifaka (Propithecus verreauxi verreauxi). I collected behavioral data from 21 individuals in 5 social groups from November 2000 to March 2002 in the Kirindy Forest (C.F.P.F.) of western Madagascar. I investigated the affiliative and agonistic behaviors of resident males and females toward other group members to determine whether residents attempt to manipulate the costs and benefits of group membership. I also examined 3 cases of immigration attempts and 1 case of emigration. As expected, group members facilitated the residency of subordinate members of the opposite sex. For example, females sought out the subordinate males, responded to their calls, and even groomed them more. However, intrasexual relationships were also important for establishing or maintaining residency. The data, in conjunction with the observations of immigration and emigration events, suggest that resident individuals of both sexes attempt to influence group size and composition. I suggest that single–male groups are not the norm in Propithecus verreauxi verreauxi because females encourage, and males do not discourage, multiple males to reside in the group to increase group stability and to reduce the risk of infanticide.     

Female social dominance and basal metabolism in a malagasy primate,Propithecus verreauxi

Tight energetic constraints on reproductively active females are hypothesized to be an important determinant of the phenomenon of female dominance in Propithecus verreauxi, a primate endemic to Madagascar. Five wild sifakas were captured in the Beza Mahafaly Special Reserve in southern Madagascar, and resting metabolic rates (RMR) were measured. Levels were low, as predicted, with the exception of a possibly pregnant female.; Although the data were not conclusive, they were consistent with the hypothesis.     

Elevation gradients of lemur abundance emphasise the importance of Madagascar’s lowland rainforest for the conservation of endemic taxa

1. Elevation gradients correlate with changes in several environmental conditions and are known to be related to animal abundance. Animals in regions with a naturally limited extent of lowland rainforest are expected to have evolved adaptations to intermediate elevations that provided a stable environment during their evolution.
2. Since the lowland rainforest of Madagascar has a limited extent and suffers from increasing anthropogenic pressure, it is essential to understand how well species tolerate intermediate and high elevations. In this study, we aim to quantify the relationship between lemur abundance and elevation in the eastern rainforest of Madagascar.
3. We correlated abundance data on 26 lemur species (10 genera), including 492 records from 26 studies, with elevation. We analysed the consistency of correlations across species with a meta-analytical approach. We controlled for species’ body mass, elevational range and median elevation. We then ran generalised linear mixed models to determine whether lemur abundance was related to elevation, body mass, plant productivity and anthropogenic disturbance.
4. Overall, the abundance of lemur species in Malagasy rainforests was negatively correlated with elevation, and species occupying broader elevational ranges showed stronger correlations. Body mass was not related to species’ tolerance of high elevations. Even though several lemur species are able to occupy the entire elevation gradient, the few remaining patches of lowland rainforests host lemur species at greater abundances than other sites. Abundance across species was negatively related to body mass, elevation and seasonality in plant productivity and positively related to plant productivity.
5. Despite the ecological flexibility of many lemur species, the remnant patches of lowland rainforests host the highest levels of lemur abundance and are key to lemur conservation. It is crucial to preserve this priority habitat both for biodiversity conservation and for our understanding of lemur adaptations.

     

Edge effects and extinction proneness in a herpetofauna from Madagascar

Edge effects are thought to play a key role in fragmented habitats. It is often assumed that edge-avoiding species are more prone to local extinction than non-edge-avoiding species, but there are few data to support this assumption. Also, few data are available on the effects of edges on some groups, and there is little understanding of seasonal changes in edge effect intensity. To better understand the role that edge effects play in fragmented tropical forests, we assessed the distribution of reptiles and amphibians in six littoral rainforest fragments in southeastern Madagascar in 1999 (dry season) and 2000 (wet season). Using randomization tests, we found all three types of edge responses: edge-avoiders, interior-avoiders, and omnipresent species. However, edge responses varied considerably among seasons. For example, some species (e.g., Mantidactylus bicalcaratus, Phelsuma quadriocellata) were strong edge-avoiders in the dry season, but showed no preference for edge or interior habitats during the wet season. Also, edge-avoiding species tended to be more extinction-prone than non-edge-avoiding species. Abiotic data documented significantly higher temperatures and dew point temperatures near edges. Wind speed also tended to be higher and relative humidity tended to be lower near edges. Our results indicate that many amphibians and reptiles respond to altered microclimates near edges and these responses have a strong seasonal component. For many species, edge sensitivity does seem to be correlated with extinction vulnerability and therefore should be of primary consideration in plans to conserve biodiversity in fragmented tropical forests.