Investigating foundations for hominin fire exploitation: Savanna-dwelling chimpanzees (Pan troglodytes verus) in fire-altered landscapes.

Humans' extensive use of fire is one behavior that sets us apart from all other animals. However, our ancestors' reliance on controlled forms of fire-i.e., for cooking-was likely preceded by a long familiarity with fire beginning with passive exploitation of naturally burned landscapes and followed by intermediate steps including active ecological modification via intentional burning. Here we explore our pyrophilic beginnings using observational data from savanna-dwelling chimpanzees. These data highlight the extent to which anthropogenic burning impacts the behavior and ecology of sympatric primates and provides an opportunity to study the ways in which apes living in a fire-altered world exploit opportunities presented by burning. Using monthly burn scar data and daily range use data we quantify the impact of burning episodes on chimpanzee habitat. Over the course of one dry season, approximately 74% of the total estimated range of the Fongoli community of savanna-dwelling chimpanzees (Pan troglodytes verus) was impacted by fire. We combine fire occurrences with behavioral data to test for relationships between burning and rate of encounter with food items and duration of subsequent patch residence time. Results show more frequent encounters and shorter patch residence times in burned areas. These data can be leveraged as a frame of reference for conceptualizing our extinct relatives' behavior around fire.

Fire's impact on threat detection and risk perception among vervet monkeys: Implications for hominin evolution.

The spatial behavior of primates is shaped by many factors including predation risk, the distribution of food sources, and access to water. In fire-prone settings, burning is a catalyst of change, altering the distribution of both plants and animals. Recent research has shown that primates alter their behavior in response to this change. Here, we study primates' perceived threat of predation in fire-modified landscapes. We focus on the predator-related behaviors of vervet monkeys (Chlorocebus pygerythrus) after controlled burning events. We compare the occurrence of vigilance and predator-deterrent behaviors, including alarm calls, scanning, and flight across different habitats and burn conditions to test the hypothesis that subjects exhibit fewer predator-specific vigilance and predator-deterrent behaviors in burned areas. The results demonstrate that predator-related behaviors occur less often in burned habitats, suggesting that predators are less common in these areas. These results provide foundations for examining hypotheses about the use of fire-altered landscapes among extinct hominins. We set these data in the context of increasing aridity, changes in burning regimes, and the emergence of pyrophilia in the human lineage.

The pyrophilic primate hypothesis.

Members of genus Homo are the only animals known to create and control fire. The adaptive significance of this unique behavior is broadly recognized, but the steps by which our ancestors evolved pyrotechnic abilities remain unknown. Many hypotheses attempting to answer this question attribute hominin fire to serendipitous, even accidental, discovery. Using recent paleoenvironmental reconstructions, we present an alternative scenario in which, 2 to 3 million years ago in tropical Africa, human fire dependence was the result of adapting to progressively fire-prone environments. The extreme and rapid fluctuations between closed canopy forests, woodland, and grasslands that occurred in tropical Africa during that time, in conjunction with reductions in atmospheric carbon dioxide levels, changed the fire regime of the region, increasing the occurrence of natural fires. We use models from optimal foraging theory to hypothesize benefits that this fire-altered landscape provided to ancestral hominins and link these benefits to steps that transformed our ancestors into a genus of active pyrophiles whose dependence on fire for survival contributed to its rapid expansion out of Africa.

What's burning got to do with it? Primate foraging opportunities in fire-modified landscapes.

OBJECTIVES: Anecdotal and formal evidence indicate that primates take advantage of burned landscapes. However, little work has been done to quantify the costs and benefits of this behavior. Using systematic behavioral observations from a population of South African vervet monkeys (Chlorocebus aethiops pygerythrus), we evaluate differences in food availability and energetics before and after controlled burns altered vegetation near their home range. We aim to determine whether burned habitats offer improved foraging opportunities. METHODS: We collected feeding data from foraging individuals and analyzed common plant foods for their energetic content. We then used the feeding and energetic data to calculate postencounter profitabilities and encounter rates for food types. Using negative binomial and mixed linear regression models we compared data from burned and unburned habitats. RESULTS: Our results show significantly improved encounter rates in burned landscapes for two prey items, invertebrates and grasses. However, postencounter profitabilities in burned areas were not significantly different than those achieved in unburned areas. CONCLUSIONS: Results suggest that improved encounters alone can motivate changes in foraging behavior. These foraging benefits enable the exploitation of burned savanna habitats, likely driving postburn range expansions observed among populations of vervet monkeys. Thus quantified, these results may serve as a foundation for hypotheses regarding the evolution of fire-use in our own lineage.

Fire and home range expansion: a behavioral response to burning among savanna dwelling vervet monkeys (Chlorocebus aethiops).

The behavioral adaptations of primates to fire-modified landscapes are of considerable interest to anthropologists because fire is fundamental to life in the African savanna-the setting in which genus Homo evolved. Here we report the behavioral responses of a savanna-dwelling primate, vervet monkeys (Chlorocebus aethiops), to fire-induced ecological change. Using behavioral and spatial data to characterize ranging patterns prior to and postburn and between burn and nonburn years, we show that these primates inhabiting small, spatially bound, riverine habitats take advantage of newly burned savanna landscapes. When subjects encountered controlled fires, they did not flee but instead avoided the path of the fire seemingly unbothered by its approach. After fire, the primates' home range expanded into newly burned but previously unused areas. These results contribute to understanding the response of non-human primates to fire-modified landscapes and can shed light on the nature and scope of opportunities and constraints posed by the emergence of fire-affected landscapes in the past. Results also expose deficiencies in our knowledge of fire-related behavioral responses in the primate lineage and highlight the need for further investigation of these responses as they relate to foraging opportunities, migration, resource use, and especially fire-centric adaptations in our own genus.