Bringing home the biggest bacon: a cross-site analysis of the structure of hunter-kill profiles in Neotropical forests

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Abstract

Forest vertebrates are critical to the subsistence of many tropical forest dwellers enjoying little or no access to other sources of animal protein. Yet the ecological and socioeconomic value of forest wildlife is being undermined as many large vertebrate populations are driven to local extinction by unsustainable hunting practices. Although large mammals that are preferred by hunters are widely variable in their morphology and ecology, they share a set of life history traits, which make them particularly vulnerable to overhunting. In this paper we compile data on game harvest from 31 tribal and nontribal settlements in Neotropical forests to examine how mammal assemblages are affected by the history of hunting within settlement catchment areas. The structure of hunter-kill profiles is related to settlement age and size in an attempt to understand how changes in hunting pressure may affect prey selectivity and the structure of residual game assemblages. There was a predictable shift from a few large-bodied to several small-bodied species harvested by increasingly older villages. Settlement persistence thus explained a significant proportion of the variation in mean body mass and species richness of mammals harvested. We conclude that differences in prey species profiles obtained by subsistence hunters of different ethnic groups can be largely explained by the local depletion status of game stocks, particularly large mammals, rather than by cultural factors.

Introduction

Subsistence hunting has been a critical form of protein acquisition for tropical forest dwellers since the earliest Stone Age hunters (Stanford and Bunn, 2001). This is particularly the case for many indigenous, mestizo and colonist communities that remain physically isolated, and have little or no access to other sources of animal protein.

Anthropologists were the first to systematically describe the issue of subsistence hunting by indigenous communities, and record settlement-based information on social and cultural factors that may affect different hunting practices and their outcomes in terms of game vertebrates consumed. In these studies, a settlement sample of hunter-kill records (hereafter, harvest profiles) were often a by-product of a more general investigation on traditional patterns of forest resource use, particularly in relation to diet.

Although the levels of indigenous protein intake often appear to be more than sufficient, the strategies used to maintain them can be extremely variable, reflecting a wide variety of cultural and ethnographic contexts involved in this subsistence activity (Balée, 1985, Beckerman, 1994). Game harvest profiles could thus be affected by feeding taboos against some target species, locally enforced bag limits on numbers of individuals killed, spatial or seasonal restrictions to hunting areas or certain species, limits on the age and sex of individuals of a prey population, and hunting technology in terms of traps and weapons used to capture different target species. However, the distinction between what could be described as culturally selected precautionary practices that may prevent future game shortages and mere adaptive responses to a history of local game depletion remains unclear.

Local extinction events in prey species assemblages is a non-random process governed by morphological, metabolic, and reproductive traits, which are usually correlated with body mass (Peters, 1983). Large body size is one of the most frequently cited traits facilitating extinction events, probably because it is associated with low reproductive rates, low population densities, long generation time and long lifespans (Hennemann, 1983, McKinney, 1997). Large game mammals may thus share a set of common life history traits that make them particularly vulnerable to overhunting. The structure of harvest profiles could thus be primarily affected by the availability of large-bodied mammals, which are often preferred game species (Peres, 1990, Alvard, 1993, Bodmer et al., 1994).

In this paper, we attempt to explain differences in the composition and relative abundance of mammal species consumed by neotropical rural folks, using a comprehensive compilation of hunting studies quantifying terrestrial vertebrate kills brought into tribal and nontribal settlements. We provide evidence that a gradual shift from large to small-bodied prey species is widespread and that cultural factors, such as feeding taboos, seem to play a minor role in determining the overall composition of target species. To that end, we relate key parameters summarising game harvest profiles to information on the age and population size of human settlements to examine how the history and scale of hunting could affect the residual mammal assemblage in a given catchment area. Finally, we discuss how prey selection by neotropical subsistence hunters could be affected by ecological rather than socio-cultural constraints.

Section snippets

Compilation criteria

Data on neotropical hunting kill records were compiled from the literature, initially on the basis of the seminal review by Redford and Robinson (1987). In addition to all studies incorporated in their analysis, an extensive search of more recently published and unpublished studies was carried out. The following selection criteria were used in compiling these studies: (1) tropical forest was the predominant vegetation type within the hunting catchment area; (2) hunting was conducted exclusively

Results

Settlements examined here were on average 193 strong (S.D.=169.9, range=25–690 inhabitants, n=31) and had been established from 2 to 25 years (mean ±S.D.=15.9±9.2 years, n=27) prior to each study. The total length of these studies varied from 28 to 877 days (237.7±187.5 days), and they recorded an average number of 259±383 mammal kills (range=30–1780) belonging to as few as seven and as many as 24 mammal species (mean=14.5±5.4 species).

The seven colonist settlements considered here did not

Discussion

A number of studies have shown that tropical forest hunters have a narrow range of preferred species that will be targeted whenever possible, regardless of their local abundance and extinction probability (Hawkes et al., 1982, Vickers, 1991, Bodmer, 1995, Fa and Peres, 2001). As predicted by optimal foraging theory, this preference is consistently skewed towards larger species yielding the greatest amount of meat per unit of energy or time allocated. For instance, the cost of shotgun cartridges

Conclusions

We have provided evidence that changes in the structure of mammal assemblages due to game hunting, as seen from the perspective of kill-profiles obtained by subsistence hunters, is a widespread phenomenon in Neotropical forests. This is consistent with estimates of the residual game abundance at forest sites subjected to varying degrees of hunting pressure, where overhunting often results in vertebrate biomass collapses, mainly through declines and local extinctions of large-bodied mammals (

Acknowledgments

We thank the authors of all hunting studies compiled here. Two of the unpublished harvest studies included in this analysis were funded by a grant from the Center for Applied Biodiversity Science of Conservation International to CAP. We thank Renata Pardini, Anina Carkeek and the participants of the 3rd Course of Quantitative Ecology and Conservation Biology at the Instituto de Pesquisas Ecológicas (IPÊ) for valuable comments on this manuscript. Financial support for AJ was provided by a

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