Local and Landscape Correlates of Primate Distribution and Persistence in the Remnant Lowland Rainforests of the Upper Brahmaputra Valley, Northeastern India

Abstract

Habitat fragmentation affects species distribution and abundance, and drives extinctions. Escalated tropical deforestation and fragmentation have confined many species populations to habitat remnants. How worthwhile is it to invest scarce resources in conserving habitat remnants within densely settled production landscapes? Are these fragments fated to lose species anyway? If not, do other ecological, anthropogenic, and species-related factors mitigate the effect of fragmentation and offer conservation opportunities? We evaluated, using generalized linear models in an information-theoretic framework, the effect of local- and landscape-scale factors on the richness, abundance, distribution, and local extinction of 6 primate species in 42 lowland tropical rainforest fragments of the Upper Brahmaputra Valley, northeastern India. On average, the forest fragments lost at least one species in the last 30 years but retained half their original species complement. Species richness declined as proportion of habitat lost increased but was not significantly affected by fragment size and isolation. The occurrence of western hoolock gibbon (Hoolock hoolock) and capped langur (Trachypithecus pileatus) in fragments was inversely related to their isolation and loss of habitat, respectively. Fragment area determined stump-tailed (Macaca arctoides) and northern pig-tailed macaque occurrence (Macaca leonina). Assamese macaque (Macaca assamensis) distribution was affected negatively by illegal tree felling, and rhesus macaque (Macaca mulatta) abundance increased as habitat heterogeneity increased. Primate extinction in a fragment was primarily governed by the extent of divergence in its food tree species richness from that in contiguous forests. We suggest the conservation value of these fragments is high because collectively they retained the entire original species pool and individually retained half of it, even a century after fragmentation. Given the extensive habitat and species loss, however, these fragments urgently require protection and active ecological restoration to sustain this rich primate assemblage.

Applying the dark diversity concept to nature conservation

“…For example, habitat fragmentation and disturbance have negatively affected primate diversity for particular lowland tropical rainforests of northeast India. Despite this, the regional, habitat-specific species pool remains conserved (Sharma et al 2013); for a given habitat fragment, the absent species remain part of that habitat's dark diversity. Where species pools are not conserved (i.e., where they are depauperate), reference assemblages cannot be expected to be successfully restored, as occurred with assemblages of fishes following river restoration in Germany .…”

Lemur catta in small forest fragments: Which variables best predict population viability?

“…The fragmentation of large and continuous forest into smaller patches leads to multiple issues regarding the viability of primate populations, and far too often, the ecological and anthropogenic pressures put on populations remaining in small forest fragments leads to extirpation (Benchimol & Peres, 2013; Bitty, Gonedele Bi, Koffi Bene, Kouassi, & McGraw, 2015; Chapman et al, 2013; Godfrey & Irwin, 2007; Sharma et al, 2013). More ecologically flexible primate species—those exhibiting dietary flexibility and found in a wide range of habitats—may stand a better chance of surviving, at least for a time, in fragmented habitat (Chapman et al, 2013; Chaves, Stoner, & Arroyo‐Rodriguez, 2012; Donati et al, 2011; Irwin et al, 2010; Pozo‐Montuy et al, 2011; Sharma et al, 2013; Mekonnen et al, 2017), but even the most flexible of species cannot withstand continuous fragmentation (Baranga et al, 2013; Harcourt & Doherty, 2005; Marsh, 2013). The ongoing breakup of formerly continuous forest leads to increased edge effects, further leading to an increase is forest dessication and susceptibility to drought (Gascon, Williamson, & da Fonseca, 2000; Laurance & Williamson, 2002; Schwitzer et al, 2011).…”

Impacts of habitat loss and fragmentation on the activity budget, ranging ecology and habitat use of Bale monkeys (Chlorocebus djamdjamensis) in the southern Ethiopian Highlands

“…Conversely, many other primates survive in forest fragments by using an energy minimizing strategy, spending less time feeding, more time resting and less time traveling (e.g., Chiropotes satanas : (Boyle & Smith, ), Alouatta seniculus : (Palma et al, ), Colobus vellerosus : (Wong & Sicotte, ), or by traveling shorter distances per day ( Propithecus diadema : (Irwin, ), Eulemur collaris : (Campera et al, )) than their counterparts in continuous forest. There are also some primate taxa that have proven largely incapable of persisting in small, isolated fragments, ultimately resulting in widespread local extirpation (e.g., Ateles geoffroyi : (Estrada & Coates‐Estrada, ); Trachypithecus pileatus : (Sharma, Madhusudan, & Sinha, )). Generally, the smaller the fragment size, the higher the probability of extirpation.…”