Agent-mediated spatial storage effect in heterogeneous habitat stabilizes competitive mouse lemur coexistence in Menabe Central, Western Madagascar

Where the small things are: Modelling edge effects on mouse lemur population density and distribution in northwestern Madagascar

Edge effects result from the penetration to varying depths and intensities, of abiotic and biotic conditions from the surrounding non-forest matrix into the forest interior. Although 70% of the world's forests are within 1 km of a forest edge, making edge effects a dominant feature of most forest habitats, there are few empirical data on inter-site differences in edge responses in primates. We used spatially explicit capture-recapture (SECR) models to determine spatial patterns of density for two species of mouse lemurs (Microcebus murinus and Microcebus ravelobensis) in two forest landscapes in northwestern Madagascar. The goal of our study was to determine if mouse lemurs displayed spatially variable responses to edge effects. We trapped animals using Sherman live traps in the Mariarano Classified Forest (MCF) and in the Ambanjabe Forest Fragment Site (AFFS) site within Ankarafantsika National Park. We trapped 126 M. murinus and 79 M. ravelobensis at MCF and 78 M. murinus and 308 M. ravelobensis at AFFS. For M. murinus, our top model predicted a positive edge response, where density increased towards edge habitats. In M. ravelobensis, our top model predicted a negative edge response, where density was lower near the forest edges and increased towards the forest interior. At regional and landscape-specific scales, SECR models estimated different density patterns between M. murinus and M. ravelobensis as a result of variation in edge distance. The spatial variability of our results using SECR models indicate the importance of studying the population ecology of primates at varying scales that are appropriate to the processes of interest. Our results lend further support to the theory that some lemurs exhibit a form of ecological flexibility in their responses to forest loss, forest fragmentation, and associated edge effects.

Determinants of habitat occupancy and spatial segregation of primates in the central Western Ghats, India

Primates are among the globally imperiled fauna requiring urgent conservation interventions to protect their habitat. Information on species distribution and factors influencing it are vital to species management and habitat protection. In this study, we assessed habitat occupancy of the lion-tailed macaque (Macaca silenus), bonnet macaque (M. radiata), and black-footed gray langur (Semnopithecus hypoleucos) that occur in the Kudremukh Wildlife Division, a large protected area network in the central Western Ghats. We examined the influence of habitat variables on the occupancy probability of these primates. We carried out four temporally replicated detection/non-detection surveys to assess detection probability and site occupancy of the primate species. We surveyed 244 sites of 5 Km², with each site surveyed for 4 days, to assess detection probability and site occupancy. Among the three species, the langur had the highest habitat occupancy estimate (0.66 ± 0.05_SE) and the lion-tailed macaque had the lowest estimate (0.28 ± 0.08_SE). The habitat occupancy estimate for the bonnet macaque was (0.56 ± 0.05_SE)_. Wet and semi-evergreen forest cover and mean elevation positively influenced the lion-tailed macaque's occurrence. Covariates influencing bonnet macaque's occurrence were plantations, semi-evergreen and moist deciduous forests, and non-forest areas. Mean elevation negatively affected its occurrence. Wet evergreen forests and plantations positively influenced the occurrence of the langur. We examined spatial segregation between the species based on their site occupancy. Pairwise comparisons revealed a significant negative association between the bonnet macaque and the other two primates. However, we found a significant positive association between the lion-tailed macaque and the langur. We discuss these results and their implications for conservation of primates in the region. Given the cost-effectiveness of carrying out surveys at large spatial scales, we recommend occupancy surveys for future surveys of forest primates.

Mouse Lemurs in an Assemblage of Cheirogaleid Primates in Menabe Central, Western Madagascar – Three Reasons to Coexist

Ecological communities are structured by interactions between coexisting species that mutually influence their distribution and abundance. Ecologically similar species are expected to exclude one another from suitable habitat, so the coexistence of two mouse lemur species in an assemblage of several closely related cheirogaleid primates in the central Menabe region of Madagascar requires explanation. We assessed the occurrence of Madame Berthe’s mouse lemurs (Microcebus berthae) and Gray mouse lemurs (Microcebus murinus), and of two larger cheirogaleids, Coquerel’s giant mouse lemur (Mirza coquereli) and the western fat-tailed dwarf lemur (Cheirogaleus medius), by nocturnal line transect walks between 2003 and 2007. We explored interspecific interactions for four different scenarios with varying resource availability (degraded and non-degraded habitat in the wet and dry season), both on the regional spatial scale and on a finer local (transect) scale. We tested whether the interspecific distribution of mouse lemur individuals indicates interspecific competition and whether their regional coexistence might be stabilized by interactions with M. coquereli or C. medius. We developed the “Inter-Species Index of Attraction” (ISIA) to quantify the observed interspecific interactions within transects and determined if these were significantly different from a null model generated by a combination of randomization and bootstrapping to control for intraspecific aggregation. For the two mouse lemurs, interspecific spatial exclusion was most pronounced during the resource-poor dry season, consistent with the hypothesis of feeding competition. Seasonally varying distribution patterns indicated resource tracking in a spatio-temporally heterogeneous environment. The interspecific distribution of individuals suggested that the larger cheirogaleids benefit M. berthae at the expense of the more abundant M. murinus: spatial associations of both, M. coquereli and C. medius, with M. murinus were negative in most scenarios and across spatial scales, but neutral or even positive with M. berthae. Thus, our study revealed that coexistence among ecologically similar heterospecifics can rely on complex density-mediated interspecific processes varying with habitat quality and season. With regard to the stability of animal assemblages, this insight has major implications for biodiversity conservation.

Effects of habitat edges on vegetation structure and the vulnerable golden-brown mouse lemur (Microcebus ravelobensis) in northwestern Madagascar

Background

Edge effects can influence species composition and community structure as a result of changes in microenvironment and edaphic variables. We investigated effects of habitat edges on vegetation structure, abundance and body mass of one vulnerable Microcebus species in northwestern Madagascar. We trapped mouse lemurs along four 1000-m transects (total of 2424 trap nights) that ran perpendicular to the forest edge. We installed 16 pairs of 20 m² vegetation plots along each transect and measured nine vegetation parameters. To determine the responses of the vegetation and animals to an increasing distance to the edge, we tested the fit of four alternative mathematical functions (linear, power, logistic and unimodal) to the data and derived the depth of edge influence (DEI) for all parameters.

Results

Logistic and unimodal functions best explained edge responses of vegetation parameters, and the logistic function performed best for abundance and body mass of M. ravelobensis. The DEI varied between 50 m (no. of seedlings, no. of liana, dbh of large trees [dbh ≥ 10 cm]) and 460 m (tree height of large trees) for the vegetation parameters, whereas it was 340 m for M. ravelobensis abundance and 390 m for body mass, corresponding best to the DEI of small tree [dbh < 10 cm] density (360 m). Small trees were significantly taller and the density of seedlings was higher in the interior than in the edge habitat. However, there was no significant difference in M. ravelobensis abundance and body mass between interior and edge habitats, suggesting that M. ravelobensis did not show a strong edge response in the study region. Finally, regression analyses revealed three negative (species abundance and three vegetation parameters) and two positive relationships (body mass and two vegetation parameters), suggesting an impact of vegetation structure on M. ravelobensis which may be partly independent of edge effects.

Conclusions

A comparison of our results with previous findings reveals that edge effects are variable in space in a small nocturnal primate from Madagascar. Such an ecological plasticity could be extremely relevant for mitigating species responses to habitat loss and anthropogenic disturbances.

Identifying Key Knowledge Gaps to Better Protect Biodiversity and Simultaneously Secure Livelihoods in a Priority Conservation Area

Global agreements like the Sustainable Development Goals (SDGs) and Achi Biodiversity Targets (ABTs) aim to secure human well-being and to protect biodiversity, but little progress has been made in reaching these aims. The key role of biodiversity in securing human well-being is rarely considered a priority – instead short-term economic profits benefiting a few are prioritized. Particularly where local livelihoods rely on resources of protected areas for immediate survival, top-down enforced biodiversity conservation often increases social inequality, hunger and poverty and thus regularly fails. Identifying key knowledge gaps helps to adjust political priority setting and investment strategies to assess conservation threats and improve natural resource management. Since acting usually occurs at a local or regional scale, we focused on a priority conservation area in one of the world’s poorest countries — the dry deciduous forests of western Madagascar. We aimed to identify key knowledge gaps in this area which need to be filled to better protect biodiversity and simultaneously ensure well-being of the local poor. We consulted 51 predominantly Malagasy experts using questionnaires. These questionnaires listed 71 knowledge gaps we collated from the literature which the experts were asked to rank by importance. Experts were encouraged to list additional knowledge gaps. Averaging the scores of all experts, we identified the top 10 knowledge gaps. Two political knowledge gaps addressing the need to determine strategies which improve law enforcement and reduce corruption ranked highest, followed by an ecological one concerning appropriate restoration and a socio–economic one regarding economic benefits locals gain from biodiversity. The general knowledge gap perceived as most important addressed strategies for long-term funding. Only one additional knowledge gap was identified: the impact of climate change-driven human migration from southwestern to central western Madagascar on socio–economic problems and its impacts on natural resources We linked the identified top 10 knowledge gaps as well as the additional knowledge gap suggested by experts to the SDGs, ABTs and 2 °C target of the Paris Climate Agreement, and discussed why these gaps were considered a priority. This research highlights important ecological, socio–economic and political research priorities and provides guidelines for policy makers and funding organizations.

Habitat orientation alters the outcome of interspecific competition: A microcosm study with zooplankton grazers

Habitat orientation has recently been demonstrated to affect the foraging behavior, growth, and production of plankton grazers. Because the orientation effect may vary with species, we hypothesize that habitat orientation may alter interspecific interactions between animal species. We experimentally investigated how habitat orientation (placing cuboid chambers in three orientations with long, medium, and small side as the chamber height) affected the interaction between two common cladoceran species, Daphnia magna and Moina micrura, which competitively exploited green algae of Chlorella pyrenoidosa at two volume scales (64 and 512 ml). Results show that chamber orientation and volume additively affected the behavior and species performance of the grazers. Specifically, both grazer species generally decreased their average swimming velocity, grazing rate (on algal cells), body size, and survival and reproduction rates with increasing chamber height for both chamber volumes and with decreasing chamber volume regardless of chamber orientation. Nevertheless, the decrease magnitude was greater for M. micrura with increasing chamber height but was greater for D. magna with decreasing chamber volume. Correspondingly, when cocultured, the density ratio of D. magna to M. micrura increased with increasing chamber height but decreased with decreasing chamber volume. At the end of the experiment, none of D. magna individuals survived in the small and short (large-based) chambers, and few M. micrura individuals survived in large and tall (small-based) chambers. These results indicate that both habitat orientation and size affect the outcome of interspecific competition between grazer species. We suggest that variation in habitat orientation may improve community coexistence and species diversity in nature.

Does habitat disturbance affect stress, body condition and parasitism in two sympatric lemurs?

Understanding how animals react to human-induced changes in their environment is a key question in conservation biology. Owing to their potential correlation with fitness, several physiological parameters are commonly used to assess the effect of habitat disturbance on animals' general health status. Here, we studied how two lemur species, the fat-tailed dwarf lemur (Cheirogaleus medius) and the grey mouse lemur (Microcebus murinus), respond to changing environmental conditions by comparing their stress levels (measured as hair cortisol concentration), parasitism and general body condition across four habitats ordered along a gradient of human disturbance at Kirindy Forest, Western Madagascar. These two species previously revealed contrasting responses to human disturbance; whereas M. murinus is known as a resilient species, C. medius is rarely encountered in highly disturbed habitats. However, neither hair cortisol concentrations nor parasitism patterns (prevalence, parasite species richness and rate of multiple infections) and body condition varied across the gradient of anthropogenic disturbance. Our results indicate that the effect of anthropogenic activities at Kirindy Forest is not reflected in the general health status of both species, which may have developed a range of behavioural adaptations to deal with suboptimal conditions. Nonetheless, a difference in relative density among sites suggests that the carrying capacity of disturbed habitat is lower, and both species respond differently to environmental changes, with C. medius being more negatively affected. Thus, even for behaviourally flexible species, extended habitat deterioration could hamper long-term viability of populations.

Geogenetic patterns in mouse lemurs (genus Microcebus) reveal the ghosts of Madagascar's forests past

Phylogeographic analysis can be described as the study of the geological and climatological processes that have produced contemporary geographic distributions of populations and species. Here, we attempt to understand how the dynamic process of landscape change on Madagascar has shaped the distribution of a targeted clade of mouse lemurs (genus Microcebus) and, conversely, how phylogenetic and population genetic patterns in these small primates can reciprocally advance our understanding of Madagascar's prehuman environment. The degree to which human activity has impacted the natural plant communities of Madagascar is of critical and enduring interest. Today, the eastern rainforests are separated from the dry deciduous forests of the west by a large expanse of presumed anthropogenic grassland savanna, dominated by the Family Poaceae, that blankets most of the Central Highlands. Although there is firm consensus that anthropogenic activities have transformed the original vegetation through agricultural and pastoral practices, the degree to which closed-canopy forest extended from the east to the west remains debated. Phylogenetic and population genetic patterns in a five-species clade of mouse lemurs suggest that longitudinal dispersal across the island was readily achieved throughout the Pleistocene, apparently ending at ∼55 ka. By examining patterns of both inter- and intraspecific genetic diversity in mouse lemur species found in the eastern, western, and Central Highland zones, we conclude that the natural environment of the Central Highlands would have been mosaic, consisting of a matrix of wooded savanna that formed a transitional zone between the extremes of humid eastern and dry western forest types.