Spatial Factors and Stochasticity in the Evaluation of Sustainable Hunting of Tapirs

Abstract

Sustainable hunting, the extraction of game without reducing its density, is a desirable approach to the use of wildlife. Assessment of sustainable extraction in many parts of the world is difficult; it has recently been done by a method proposed by Robinson and Redford (1991): a maximum number of animals that can be extracted per unit area is calculated based on life-history parameters and density estimates. If extraction is higher than that maximum number, it is deemed unsustainable. We extended the method by adding spatial and stochastic components through an individual-based model of a population of female tapirs ( Tapirus sp.) and conducted a sensitivity analysis to evaluate the importance of spatial and life-history parameters. Our analysis suggests that spatial factors, such as the shape of the hunted area and the size of the surrounding population, may be important in determining the sustainability of extraction. For long-lived, slow-reproducing mammals such as tapirs, survival to age of last reproduction is the most critical parameter, but the shape of the hunting zone and population density can be critical, especially in unsustainable hunting scenarios. We advocate long-term studies of tapirs to collect information on spatial movements and survival rates that could then be used for development of proper management plans. Factores Espaciales y Estocasticidad en la Evaluación de la Cacería Sustentable de TapiresResumen: La cacería sustentable, extracción de animales de caza sin reducción de su densidad, es un enfoque deseable para el uso de vida silvestre. La evaluación de la extracción sustentable es difícil en muchas partes del mundo y se ha hecho utilizando un método propuesto por Robinson y Redford (1991): el número máximo de animales que se puede extraer por unidad de área se calcula con base en parámetros de la historia de vida y estimaciones de la densidad. Si la extracción es mayor que ese número máximo, se considera no sustentable. Extendimos el método agregando componentes espaciales y estocásticos por medio del modelo basado en individuos de una población de tapires ( Tapirus sp.) hembras y realizamos un análisis de sensibilidad para evaluar la importancia de los parámetros espaciales y de la historia de vida. Nuestro análisis sugiere que factores espaciales, tal como la forma del área de cacería y el tamaño de la población circundante, pueden ser importantes en la determinación de la sustentabilidad de la extracción. Para especies longevas de reproducción lenta como el tapir, la supervivencia hasta la última edad reproductiva es el parámetro más crítico; pero la forma del área de cacería y la densidad pueden ser críticas, especialmente en poblaciones bajo caza no sustentable. Recomendamos estudios de largo plazo de tapires para obtener información de movimientos espaciales y tasas de supervivencia que pueda utilizarse para el desarrollo de planes de manejo adecuados.

The uncovered volumes of bushmeat commercialized in the Amazonian trifrontier between Colombia, Peru & Brazil

“…Yet, the study was based on the use of the over simplified Robinson and Redford (1992) model, which does not take spatial factors in to account. Shape of the hunted area and the size of the surrounding population are key factors that influence the sustainability of tapir hunting (Salas and Kim 2002;Novaro et al 2000).…”

Impact of game hunting by the Kayapó of south-eastern Amazonia: implications for wildlife conservation in tropical forest indigenous reserves

“…However, tapirs continue to be harvested at very high levels although they have become extremely rare in the vicinities of A'Ukre. This suggests that most of the tapirs killed in the core catchment were immigrants drawn from surrounding underharvested (or unhunted) areas as predicted by healthy patterns of landscape scale dispersal across a range of exploitation levels (Novaro et al 2000;Salas and Kim 2002). This is only possible because of the vast area of uninhabited primary forest surrounding the village catchment, which serves as a year-round source of immigrants.…”

Managing hunting under uncertainty: from one-off ecological indicators to resilience approaches in assessing the sustainability of bushmeat hunting

“…Milner-Gulland and Akçakaya (2001) and van Vliet and Nasi (2008) showed that the major problems related to the use of simple biological indicators are paucity of available biological data even for the most common species and the difficulty of collecting data needed for a full sustainability assessment. Several authors have suggested that models for calculating sustainable harvest may produce conservative estimates (Alvard et al 1997, Robinson and Bodmer 1999, Noss 2000, Novaro et al 2000 and report levels of harvest above sustainable values, yet these levels have been maintained or increased over time with no sign of population depletion (Salas and Kim 2002). Moreover, the use of one-off sustainability indicators requires extensive fieldwork that must be repeated for each new study site if quantitative measures of game offtake or animal stocks are to be obtained (Robinson and Bodmer 1999, Sirén et al 2004, Ohl-Schacherer et al 2007, Smith 2008.…”

“…Studies on sustainable hunting using spatially explicit individual-based models (Novaro et al 2000, Salas and Kim 2002, van Vliet et al 2010) have tested the role of landscape structure and dispersal characteristics that might influence the sustainability of hunting. Salas and Kim (2002) suggest that spatial factors, e.g., the shape of the hunted area and the size of the population in surrounding areas, are important in determining the harvest sustainability. Novaro et al (2000) found that dispersal has a key role in rebuilding animal populations depleted by hunting.…”