Species‐area relationships of lemurs in a fragmented landscape in Madagascar

Abstract

We used species-area relationships (SARs) to investigate the effects of habitat loss on lemur biogeography. We measured species richness via visual surveys on line transects within 42 fragments of dry deciduous forest at the Ambanjabe field site in Ankarafantsika National Park, Madagascar. We measured human disturbance and habitat characteristics within 38 of the 42 fragments. We measured the distance between each fragment and the nearest settlement, continuous forest, and nearest neighboring fragment. We fit 10 candidate SAR models to the data using nonlinear least squares regression and compared them using Akaikeʼs Information Criterion (AIC). To determine how habitat characteristics, as well as area, influenced species richness, we ran a hierarchical partitioning procedure to select which variables to include in generalized additive models (GAMs) and compared them using AIC.Contrary to expectations, we found that lemurs form convex SARs, without a "small island effect", and with the power model being the most likely SAR model. Although we found that four variables (area, survey effort, and total human disturbance, and mean tree height) independently contributed greater than 10% of the variation in lemur species richness, only area was included in the most likely model. We suggest that the power model was the most likely SAR model and our inability to detect a "small island effect" are the result of Microcebus spp. being edge tolerant and capable of dispersing through matrix, scale issues in the study design, and low γ-diversity in the landscape. However, more study is needed to determine what role human disturbance plays in influencing species richness in lemurs. K E Y W O R D Sarea, habitat loss, patches, power model, sigmoidal model

Trends in forest fragment research in Madagascar: Documented responses by lemurs and other taxa

“…Lemur sources: a, Brenneman et al (2012); b, encounter rate only: Craul et al. (2009); c, trap success only: Farris et al (2014); d, Ganzhorn (2003); e, population size only: Ganzhorn et al (2000); f, Marrocoli et al (2013); g, pres/abs of only one species: Miller et al (2017); h, Norscia (2008); i, population size only: Norscia and Palagi (2011); j, trap success only: Ramanamanjato and Ganzhorn (2001); k, Randrianambinina et al (2010); l, encounter rate only: Schüßler et al (2018); m, Seiler et al (2013); n, Steffens and Lehman (2018); o, Steffens and Lehman (2019).…”

“…Craul et al (2009) did not find any Milne‐Edwards’ sportive lemur ( L. edwardsi ), its target species, in the majority of its study fragments ( n = 6), but this does not appear to be related to fragment size. In an examination of factors influencing lemur species richness across 42 fragments, Steffens and Lehman (2019) found fragment area to be the sole predictor in their best model (best model weight, of 15 models: 0.35; 10 total variables explored, including isolation, human disturbance, habitat characteristics, and sampling metrics).…”

“…Although every fragmented landscape is unique, the wide variety of fragment metrics employed across examined studies in Madagascar, an unclear distinction between “fragments” and “continuous” forests, and the breadth of tests employed to examine fragmentation's effects, indicate the challenge of working across nonstandardized definitions of fragmentation (Ewers & Didham, 2006; for primates: Arroyo‐Rodríguez et al, 2013). Several studies in this sample explicitly stated the criteria they used to define fragments (Brinkmann et al, 2014; De Haulleville et al, 2018; Steffens & Lehman, 2019), with some attributing definitions to large‐scale land classification methods (Bogaert, Ceulemans, & Salvador‐Van Eysenrode, 2004; Riitters et al, 2002). However, even with carefully defined fragments, the wealth of factors to consider beyond those commonly employed when testing fragmentation (e.g., area and isolation distance), such as the history of the surrounding matrix (Klanderud et al, 2009), measures of internal fragmentation (Cadotte & Lovett‐Doust, 2007), and fragment shape (Watson, Whittaker, & Dawson, 2004b), further complicate the ability to generalize fragmentation's impact (Ewers & Didham, 2006).…”

“…Nevertheless, the most consistent factor reported for influencing species’ response to fragmentation is fragment area (e.g., Quesnelle, Fahrig, & Lindsay, 2013; Steffens & Lehman, 2019), particularly as it is commonly correlated with multiple other metrics (Ewers & Didham, 2006). The consideration of fragment size may be particularly important when studying non‐human primates, as a potential threshold has been proposed beyond which primate populations are not expected to persist.…”

Occurrence of lemurs in landscapes and their species‐specific scale responses to habitat loss

“…However, C. medius is relatively larger in body mass, frugivorous, and hibernates between April and October (Dausmann, Glos, Ganzhorn, & Heldmaier, 2005). We conducted our study in the dry season and early part of the wet season (May–November) to facilitate access and observations of lemurs (Steffens & Lehman, 2019).…”