Morphometric signals of population decline in diademed sifakas occupying degraded rainforest habitat in Madagascar

Abstract

Anthropogenic habitat change can have varied impacts on primates, including both negative and positive outcomes. Even when behavioural shifts are seen, they may reflect decreased health, or simply behavioural flexibility; understanding this distinction is important for conservation efforts. This study examines habitat-related variation in adult and immature morphometrics among diademed sifakas ( Propithecus diadema ). We collected morphometric data from sifakas at Tsinjoarivo, Madagascar (19 years, 188 captures, 113 individuals). Captures spanned 12 groups, five within continuous forest (“CONT”), and seven in degraded fragments (“FRAG”) where sifakas have lower nutritional intakes. Few consistent differences were found between CONT and FRAG groups. However, using home range quality as a covariate rather than a CONT/FRAG dichotomy revealed a threshold: the two FRAG groups in the lowest-quality habitat showed low adult mass and condition (wasting), and low immature mass and length (stunting). Though less-disturbed fragments apparently provide viable habitat, we suggest the sifakas in the most challenging habitats cannot evolve fast enough to keep up with such rapid habitat change. We suggest other long-lived organisms will show similar morphometric “warning signs” (wasting in adults, stunting in immatures); selected morphometric variables can thus be useful at gauging vulnerability of populations in the face of anthropogenic change.

Do functional traits offset the effects of fragmentation? The case of large‐bodied diurnal lemur species

“…It should be noted that while P . diadema inhabit some fragmented forests, the long‐term viability of these populations is unknown as previous research has suggested that smaller habitats can lead to morphometric signals of population decline (Irwin et al, 2019).…”

“…At Berenty in the far south, P. verreauxi inhabits small degraded fragments that are associated with an abundance of protein-rich foods, potentially allowing this species to maintain relatively high densities (Norscia & Palagi, 2008). It should be noted that while P. diadema inhabit some fragmented forests, the long-term viability of these populations is unknown as previous research has suggested that smaller habitats can lead to morphometric signals of population decline (Irwin et al, 2019).…”

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

“…Three studies included examinations of parasite load, with all reporting increased measures of parasitic infection with increased fragmentation ( E. collaris : Balestri et al, 2014; Lazdane, Broll, Theisinger, Bearder, & Donati, 2014; M. murinus : Raharivololona & Ganzhorn, 2009). While diademed sifaka ( P. tattersalli ) living in fragments were found to display signs of wasting in adults and stunting in immatures (Irwin et al, 2019) and to have lower white blood cell counts and zinc and iron levels, among other measures (Irwin, Junge, Raharison, & Samonds, 2010). Morphometric signals were most pronounced in fragment groups occupying the lowest quality home ranges, indicative of the importance of accounting for fragment disturbance (Irwin et al, 2019).…”

“…While diademed sifaka ( P. tattersalli ) living in fragments were found to display signs of wasting in adults and stunting in immatures (Irwin et al, 2019) and to have lower white blood cell counts and zinc and iron levels, among other measures (Irwin, Junge, Raharison, & Samonds, 2010). Morphometric signals were most pronounced in fragment groups occupying the lowest quality home ranges, indicative of the importance of accounting for fragment disturbance (Irwin et al, 2019). Serum biochemical profiles by Junge et al (2011) additionally identified baseline trace mineral levels for indri ( I. indri ) living in close proximity to a proposed mine site.…”

Realized distribution patterns of crowned lemurs (Eulemur coronatus) within a human‐dominated forest fragment in northern Madagascar

“…Moreover, the lack of direct, conflictive interactions (i.e., hunting or crop-raiding) between E. coronatus and the local Malagasy communities is likely another major factor supporting the proximity and cohabitation of these two populations (Missouri Botanical Garden, 2015;Mercado Malabet, 2017). has influenced the health of this population (Balestri et al, 2014;Irwin et al, 2019;Tecot, 2012).…”