Environment and time as constraints on the biogeographical distribution of gibbons

Abstract

We develop a time budget model for the hylobatid family with the aim of assessing the extent to which their contemporary and historical biogeographic distributions might be explained by ecological constraints. The model uses local climate to predict time budgets, and from this the limiting size of social group that animals could manage at a given location. The model predicts maximum group sizes that vary between 3 and 15 within the taxon's current distribution, indicating that the combination of their dietary and locomotor styles with the kinds of habitats they inhabit radically constrain group size. Beyond the edges of their current distribution, sustainable group size rapidly tends to zero, although if they had been able to bypass some of these areas, they would have found very suitable habitats in southern India and beyond the Wallace Line. While travel time would be a major constraint on group size at larger group sizes, as it is in great apes, the main factor limiting the gibbon's current distribution is the time they need to spend resting that is imposed on them by the environment. The model also indicates that gibbons would not now be able to survive in regions of central and southeastern China where they are known to have occurred within historical times, perhaps because historical climate change following the Little Ice Age of the C18th made these regions uninhabitable for them. Finally, our results indicate that gibbons have the ecological capacity to live in larger groups than they do, making it unlikely that their adoption of monogamy reflects purely ecological constraints.

Female Dispersion Is Necessary, But Not Sufficient, For The Evolution of Monogamy in Mammals

“…Nomascus and Leontopithecus occupy more marginal habitats compared to other members of their respective families (Dunbar et al 2019;Rylands 1989;Kierulff & Rylands 2003). Given these results and the fact that evidence from models of time budgets (Dunbar et al 2009(Dunbar et al , 2019Korstjens et al 2018) suggests that, except on the limits of their biogeographical distributions, most primates are not under as much ecological pressure as has usually been assumed, this effectively rules out any likelihood that the females of monogamous species are forced to live alone due to ecological competition. Brotherton & Manser (1997) suggested that the problem might be that males are unable to prevent rivals mating with their females if several are in oestrus simultaneously in different locations.…”

“…In fact, comparative analyses cast doubt on the role of foraging: they suggest that monogamous female mammals do not necessarily live in larger territories than species where females live in groups, even though their densities might be lower (Dunbar 1988;Lukas & Clutton-Brock 2013). More importantly, time budget models for monogamous gibbons (Dunbar et al 2019) and other medium-sized arboreal primates (Korstjens & Dunbar 2007;Korstjens et al 2018) indicate that, except on the margins of their biogeographical distributions, there is nothing in their ecology to prevent them living in significantly larger social groups than they actually do.…”

The Social Role of Self-Control

“…Similarly, large home ranges are assumed to be cognitively demanding in terms of the mental mapping skills and the fact that foraging animals have to choose between near and distant locations on the basis of their profitability [4,34]. In primates, both percent fruit in the diet and range size are strongly influenced by habitat conditions and hence impact on nutrient acquisition [35][36][37][38][39]. If inhibition relates to foraging efficiency, it should correlate positively with one or both of these indices.…”

Influence of food availability and climate on behavior patterns of western black crested gibbons (Nomascus concolor) at Mt. Wuliang, Yunnan, China

“…How animals allocate time to activities is one of the most important questions in animal ecology (Dunbar et al, ). Behavior patterns reflect how animals cope with seasonal environmental variation, revealing how energy intake and expenditure are balanced to meet the needs of survival and reproduction (Chaves, Stoner, & Arroyo‐Rodríguez, ; Hanya, ; Korstjens, Lehmann, & Dunbar, ; Sayers & Norconk, ; Vasey, ; Weerasekara & Ranawana, ).…”

“…Food availability is widely recognized as one of the most important factors that constrains animals’ activity budget (Chaves et al, ; Sayers & Norconk, ; Vasey, ). Animals have to allocate their limited time toward multiple needs, most of which are related to fitness (i.e., foraging, traveling, resting, and social behavior; Dunbar et al, ). Schoener () proposed that animals must make trade‐offs between energy intake and expenditure during foraging.…”