Achilles heel of a powerful invader: restrictions on distribution and disappearance of feral pigs from a protected area in Northern Pantanal, Western Brazil.

Jose L.P Cordeiro,Luiz Flamarion B Oliveira,Carlos Fonseca,Gabriel S Hofmann

doi:10.7717/peerj.4200

Abstract

This paper focuses on a rare case of natural disappearance of feral pigs (Sus scrofa) in an extensive area without using traditional methods of eradication programs. The study was conducted both in the Private Reserve of Natural Heritage (PRNH) Sesc Pantanal and in an adjacent traditional private cattle ranch. In 1998, feral pigs were abundant and widely distributed in the PRNH. However, the feral pigs gradually disappeared from the area and currently, the absence of pigs in the PRNH contrasts with the adjacent cattle ranch where the species is abundant. To understand the current distribution of the species in the region we partitioned the effects of variation of feral pigs’ presence considering the habitat structure (local), landscape composition and the occurrence of potential predators. Additionally, we modeled the distributions of the species in Northern Pantanal, projecting into the past using the classes of vegetation cover before the PRNH implementation (year 1988). Our results show areas with more suitability for feral pigs in regions where the landscape is dominated by pastures and permeated by patches of Seasonal Dry Forest. The species tends to avoid predominantly forested areas. Additionally, we recorded that the environmental suitability decreases exponentially as the distance from water bodies increases. The disappearance of feral pigs in the PRNH area seems to be associated with changes in the landscape and vegetation structure after the removal of the cattle. In the Brazilian Pantanal, the feral pigs’ occurrence seems strongly conditioned to environmental changes associated to livestock activity.

Highlights

The different morphotypes of Sus scrofa Linnaeus - wild boar, domestic and wild pigs - are the most widespread exotic ungulates in the world, with populations in demographic and spatial expansion in almost all Eurasian countries (Fonseca & Correia, 2008 ) and in most of the regions where they were introduced (Australia, South and North America)
We evaluated the size of the gradient through Detrended Canonical Correspondence Analysis (DCCA; ter Braak 1986; ter Braak & Smilauer 2002), considering the feral pigs Index of Use (IU) as a response variable in each sample unit and the predators IU, and habitat structure and landscape classes of cover as environmental data
Only one variable which describes habitat structure and three axis related to landscape features

Summary

Introduction

The different morphotypes of Sus scrofa Linnaeus - wild boar (javali), domestic (different breeds) and wild pigs (feral) - are the most widespread exotic ungulates in the world, with populations in demographic and spatial expansion in almost all Eurasian countries (Fonseca & Correia, 2008 ) and in most of the regions where they were introduced (Australia, South and North America). Sus scrofa have several biological traits and strong invasive abilities that allow them to occupy different habitat types throughout their exotic distribution range, making the eradication of this species (feral pigs) very difficult and expensive (Mccann and Garcelon 2008; Morrison et al 2007; Parkes et al 2010). When compared to other ungulate species, wild boar show several attributes that are typical of r-strategists (Geisser and Reyer 2005). They have the highest reproductive rate among ungulates, and their local density can double in one year (Massei et al 1997). The species has high ecological plasticity, a very opportunistic feeding behavior and a generalist approach to landscape use (Gabor and Hellgren 2000; Geisser and Reyer 2005)

Methods

Results

Discussion

Conclusion