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

Abstract

1. Elevation gradients correlate with changes in several environmental conditions and are known to influence 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 assessed the relationship between species' body mass and elevational gradients of abundance, and controlled for species' elevational range and median elevation. We then ran generalised linear mixed models to determine whether encounter rates were influenced by 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 did not influence species' tolerance of high elevations. Even though several lemur species showed tolerance to the elevation gradient, the few remaining large 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 and anthropogenic disturbance. 5. Despite the ecological flexibility of many lemur species, the largest 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.

Environmental drivers of Cheirogaleidae population density: Remarkable resilience of Madagascar’s smallest lemurs to habitat degradation

“…As all lemurs require forest habitat for their survival and many species are sensitive to habitat degradation (Schwitzer et al, 2013), I predicted that population density of all genera would correlate positively with vegetation-related variables and negatively with anthropogenic disturbance. However, due to the results of previous studies (Campera et al, 2020;Kamilar et al, 2016;Setash et al, 2017), I also predicted that population density would correlate positively with the abiotic variables temperature and precipitation, and negatively with elevation.…”

“…Habitat degradation and disturbance have also been demonstrated to have mostly negative effects on the population density of lemurs (Ganzhorn et al, 1997;Lehman et al, 2006a), and the population responses to these anthropogenic drivers are often reported as species-specific (Eppley et al, 2020;Herrera et al, 2011;Lehman et al, 2006b;Steffens et al, 2020). High population density variation has been observed along several environmental gradients, and there is evidence of both positive and negative correlations between lemur density and elevation (Campera et al, 2020;Goodman & Ganzhorn, 2004) and negative correlations with water availability (Axel & Maurer, 2011). There is also evidence to suggest that optimal climatic conditions (Kamilar et al, 2016), vegetation quality and productivity (Ganzhorn, 1995), and food availability (Steffens & Lehman, 2016) may also positively influence lemur population density.…”

“…In this study, I aimed to determine the primary drivers of population density of each of the five Cheirogaleidae genera using density data published within the literature. I opted to use a genus-level approach in this investigation as the general ecology and natural history of the species within genera are highly similar (Lehman et al, 2016;Mittermeier et al, 2010;Radespiel, 2006), and each lemur genus has a distinct ecological niche (e.g., Campera et al, 2019;Kamilar & Muldoon, 2010;Lahann, 2008); while niche separation and divergence does exist among sympatric congeners on an often local or site-specific scale (e.g., Dammhahn & Kappeler, 2008;Lahann, 2007Lahann, , 2008Radespiel et al, 2003;Rakotondravony & Radespiel, 2009;Thorén et al, 2011), the broad effect of biogeography and environmental variables on lemurs over a large area often follows a trend (e.g., Campera et al, 2020;Herrera, 2017;Pearson & Raxworthy, 2009;Setash et al, 2017). The specific objectives of this study were:…”

“…As different lemur groups have often been observed to respond interspecifically to different environmental variables (e.g., Campera et al, 2020;Herrera et al, 2011;Kamilar et al, 2016;Lehman et al, 2006b), I hypothesized that relationships between population density and the environmental variables would be highly specific to each of the five Cheirogaleidae genera. As all lemurs require forest habitat for their survival and many species are sensitive to habitat degradation (Schwitzer et al, 2013), I predicted that population density of all genera would correlate positively with vegetation-related variables and negatively with anthropogenic disturbance.…”

Identification of crucial stepping stone habitats for biodiversity conservation in northeastern Madagascar using remote sensing and comparative predictive modeling

“…Even single IRSs can be of particular importance for micro-endemic species like mouse lemurs (Radespiel et al 2008(Radespiel et al , 2012, amphibians (Gehring et al 2010;Vences et al 2010) or reptiles (Gehring et al 2010). Furthermore, the lowland rain forests of eastern Madagascar have been stated the key for lemur conservation in the long term (Campera et al 2019). At least two of these IRSs are predicted to have almost no areas of low deforestation probability (fields C7 and D8 as well as field D6 in Fig.…”