Berenty 2006: Census of Propithecus verreauxi and Possible Evidence of Population Stress

Abstract

We provide a survey of a folivorous lemur, Propithecus verreauxi (sifaka), in the Berenty Reserve, southern Madagascar. Higher densities of folivores in small patches occur in either high-quality food areas or in less disturbed refugia. The skewness of sex ratio, which in lemurs is often male-biased, can be critically exacerbated in population stress. We predicted that sifaka would show higher densities in areas where protein-rich food is abundant (prediction 1a) and in refugium areas (prediction 1b). Owing to increased competition by brown and ringtailed lemurs and decreased food production by tamarind trees, we expected an extremely male-biased sex ratio (prediction 2). In November-December 2006, we counted and sexed 206 adult/subadult sifaka (49 groups) during daily walks in different forest zones (Ankoba secondary forest, to the north, Malaza gallery/scrub areas, and spiny forest, to the south). Sifaka may have decreased in the gallery forest to concentrate in Ankoba (in a sort of out-of-Malaza). The area contains protein-rich food (prediction 1a confirmed). Sifaka are proportionally more concentrated in the spiny area than in the degraded scrub forest (prediction 1b confirmed). The sex ratio is extremely male biased, possibly due to either high sifaka density, in Ankoba, or food availability reduction, in Malaza (prediction 2 confirmed). The sifaka population seems to be under stress: researchers need to resume demographic studies, interrupted in Berenty in the mid-1980s, to preserve in situ a species that is difficult to protect ex situ.

Noninvasive genetic assessment of the population trend and sex ratio of the Shennongjia population of Sichuan snub-nosed monkeys (Rhinopithecus roxellana)

“…An alternative, nonmutually exclusive explanation for our results is that the population genuinely exhibits a female-biased sex ratio. Deviations from an equal sex ratio are common in mammalian populations and, according to a complex framework of models and hypotheses, either adaptive mechanisms (social or parental control of sex ratio from conception onward [41,42]) or nonadaptive ones, e.g., unpredictable environmental events leading to different mortality rates in the sexes [43,44], can shift primate sex ratios from parity [45]. Future work employing a more extensive genetic census of the population will serve to refine the estimate of the population sex ratio.…”

Mating First, Mating More: Biological Market Fluctuation in a Wild Prosimian

“…Group composition and sex-ratio were typical for the study species in general [49] and for the study population in particular [50] (cf. Table 1).…”

Lemurs in a complex landscape: mapping species density in subtropical dry forests of southwestern Madagascar using data at multiple levels

“…Simultaneous sampling of the two sympatric lemur species has been rare, apart from Berenty Reserve where both lemurs have been censused at sporadic intervals since the early 1960s [Jolly, 1972;Jolly & Pride, 1999;Norscia & Palagi, 2008]. Simultaneous sampling took place in 1970, when Jolly [1972] recensused both species in a 10 ha study area of the gallery forest; however, no comparisons were made between densities of the two species.…”