Predator avoidance and dietary fibre predict diurnality in the cathemeral folivore Hapalemur meridionalis

Abstract

Though numerous mammalian taxa exhibit cathemerality (i.e., activity distributed across 24-h cycle), this includes very few primates, exceptions being species from Aotinae and Lemuridae. Four non-mutually exclusive hypotheses have been proposed to explain ultimate determinants for cathemeral activity in lemurs: thermoregulatory benefits, anti-predator strategy, competition avoidance, and metabolic dietary-related needs. However, these have only been explored in the frugivorous genus Eulemur, with some species increasing nocturnality as a possible response to avoid diurnal raptors and to increase their ability to digest fibre during resource scarce periods. Since Eulemur lack specialisations for digesting bulk food, this strategy would allow for processing fibres over the full 24-h. The folivorous lemurids, i.e., genus Hapalemur, provide a divergent model to explore these hypotheses due to gastrointestinal adaptations for digesting dietary fibre and small body size compared to Eulemur. We linked continuous activity data collected from archival tags with observational behaviour and feeding data from three groups of adult H. meridionalis from JanuaryDecember 2013. We tested the effects of thermoregulation, anti-predator, and the weighted proportion of dietary fibre on the daily diurnal/nocturnal activity ratio using a Linear MixedModel. Our best-fit model revealed that increased canopy exposure and dietary fibre predicted greater diurnality. Our findings contrast with previous predictions for frugivorous lemurids, proposing a divergent adaptive explanation for folivorous lemurids. We suggest that the need to avoid terrestrial predators, as well as the longer digestive bouts during periods of bulky food, may override cathemerality in favour of diurnality in these bamboo lemurs.

Daily activity and diet of Talaud bear cuscus (Ailurops melanotis Thomas, 1898) on Salibabu Island, North Sulawesi, Indonesia

“…Furthermore, according to Donati et al (2006) and Eppley et al (2016), there are at least 4 hypotheses proposed to explain the determinants for cathemeral activity: thermoregulatory benefits, anti-predator strategy, competition avoidance and metabolic dietary-related needs. While based on Diete et al (2017), variation, fixity, and plasticity in activity patterns can be influenced by factors such as season and habitat (temporal resource availability).…”

Abiotic Factors Affecting the Cathemeral Activity of Eulemur fulvus in the Dry Deciduous Forest of North-Western Madagascar

“…Donati and Borgognini-Tarli [2006b] found that the nocturnal activity of E. collaris correlated negatively with rainfall and humidity, but linked this association to the decrease in lunar luminosity due to cloud cover. Eppley et al [2017] did not find a strong association between the amount of rainfall and the ratio of diurnal to nocturnal activity in Hapalemur meridionalis, nor did Kappeler and Erkert [2003] in E. rufifrons. Many cathemeral primates have been shown to increase diurnal activity and decrease nocturnal activity during the wet season [Andrews and Birkinshaw, 1998;Curtis et al, 1999;Donati et al, 1999;Rasmussen, 1999;Kappeler and Erkert, 2003;Tarnaud, 2006;Eppley et al, 2015].…”

“…However, it is conceivable that bright nights may also offer some benefits that possibly outweigh the predation risk. For example, bright nights may allow an "early detection strategy" to avoid predators [see Gursky, 2003;Colquhoun, 2006;Fichtel, 2007;Prugh and Golden, 2014] and/or may improve foraging efficiency [Curtis et al, 1999;Donati et al, 1999;Valenta et al, 2016; see also Eppley et al, 2017]. Alternatively, sleeping at night could also be risky for lemurs (see, e.g., the predation of Propithecus diadema in their sleeping trees by Cryptoprocta ferox) [Wright et al, 1997].…”

“…Cathemeral primates perform significant amounts of activity, particularly feeding and/or travelling, during both the light and dark portions of a 24-h period [Tattersall, 1987]. Among wild primates, cathemerality has been reported in haplorrhines in the genus Aotus [Fernandez-Duque et al, 2001;Fernandez-Duque, 2003;Fernandez-Duque and Erkert, 2006] and among Malagasy strepsirrhines in the family Lemuridae, including Eulemur [Curtis et al, 1999;Kappeler and Erkert, 2003;Donati and Borgognini-Tarli, 2006a, b;Schwitzer et al, 2007;reviewed in Donati et al, 2016], Hapalemur [Eppley et al, 2015[Eppley et al, , 2017, and Lemur [Donati et al, 2013] and in the Indriidae genus Avahi [Campera et al, 2019].…”

Huddling is more important than rest site selection for thermoregulation in southern bamboo lemurs

“…Southern bamboo lemurs (H. meridionalis) are medium-sized lemurs (albeit smallbodied primates) with an average body mass of 1.1 kg that exhibit a cathemeral activity pattern (Eppley et al 2015b(Eppley et al , 2015c(Eppley et al , 2017. This species is also known to feed heavily on a low-quality folivorous diet, the bulk of which is composed of various terrestrial grasses and sedges (Eppley et al 2011(Eppley et al , 2016a.…”