How immunocontraception can contribute to elephant management in small, enclosed reserves: Munyawana population as a case study.

Heleen C Druce,Rob Slotow,Robin L Mackey,Matt Hayward

doi:10.1371/journal.pone.0027952

Abstract

Immunocontraception has been widely used as a management tool to reduce population growth in captive as well as wild populations of various fauna. We model the use of an individual-based rotational immunocontraception plan on a wild elephant, Loxodonta africana, population and quantify the social and reproductive advantages of this method of implementation using adaptive management. The use of immunocontraception on an individual, rotational basis stretches the inter-calving interval for each individual female elephant to a management-determined interval, preventing exposing females to unlimited long-term immunocontraception use (which may have as yet undocumented negative effects). Such rotational immunocontraception can effectively lower population growth rates, age the population, and alter the age structure. Furthermore, such structured intervention can simulate natural process such as predation or episodic catastrophic events (e.g., drought), which regulates calf recruitment within an abnormally structured population. A rotational immunocontraception plan is a feasible and useful elephant population management tool, especially in a small, enclosed conservation area. Such approaches should be considered for other long-lived, social species in enclosed areas where the long-term consequences of consistent contraception may be unknown.

Highlights

Within natural, open conservation systems, large stochastic events such as drought, fire and predation keep populations at a sustainable level by eliminating the old, weak and young [1,2,3,4]
This study showed that a rotational approach to an immunocontraception plan can be a useful tool to age a population and thereby stabilise its age structure; yield a reduced population growth and prevent irruption of young populations; allow for management of populations, family groups and individuals in relatively small reserves enclosed by fences
The results provide some insight into which demographic parameters may be most important for determining rate of population growth

Summary

Introduction

Open conservation systems, large stochastic events such as drought, fire and predation keep populations at a sustainable level by eliminating the old, weak and young [1,2,3,4]. Within modern conservation areas, especially small, enclosed reserves, natural stochastic events are altered by human management interventions [3], with more intervention required for smaller reserves [5] Within these conservation areas, the occurrences and spread of big fires are often prevented or controlled [4], while natural droughts have limited effects on wildlife populations, as critical resources are usually never a limiting factor due to water and food provision [6,7]. The fences prevent natural movement patterns from and into these areas, and predation events are effected and controlled within these areas, as managers determine and restrict the predator-prey ratios, and predator population structure [5,8] This can result in eruption of populations which leads to significant environmental problems [9,10], which require active management intervention [11,12,13,14]. For management interventions to be effective and non-detrimental, a sound understanding of the natural processes is required

Methods

Results

Conclusion