Spatial Niche Expansion at Multiple Habitat Scales of a Tropical Freshwater Turtle in the Absence of a Potential Competitor

Fabio Petrozzi,Sery Gonedele Bi,Nic Pacini,Luca Luiselli,Daniele Dendi,Julia E Fa,Stephanie N Ajong

doi:10.3390/d13020055

Abstract

Resource partitioning, the division of limited resources by species to help avoid competition, has been observed in freshwater turtle assemblages in several natural systems but has rarely been studied in tropical African ecosystems. Here, we investigate habitat preferences of two congeneric species in the family Pelomedusidae, Pelusios castaneus and P. cupulatta, in riverine/wetland habitats in the southern Ivory Coast (West Africa). Pelusios castaneus is a widespread species across West-central African savannahs and open forests, whereas P. cupulatta is endemic to the Upper Guinean forest region in West Africa. The two species have a similar diet composition (mainly carnivorous) but diverge considerably in body size, P. cupulatta being much larger. We use hand-fishing-nets and fishing funnel traps to record turtles in 18 distinct sites and analyze habitat preferences by species at two spatial scales. At a macro-habitat scale, P. castaneus is captured mainly in marshlands, whereas P. cupulatta is found in both rivers and wetlands. The two species differ significantly in their use of: (i) banks (P. castaneus being found primarily in spots with grassy banks, whereas P. cupulatta is found in spots with forested banks), and (ii) aquatic vegetation (P. cupulatta prefers spots with more abundant aquatic vegetation than P. castaneus), but both species select sites with no or moderate current. Additionally, in sites where P. cupulatta is not found, P. castaneus expands its spatial niche at multiple habitat scales, notably invading waterbodies with forested banks. Our results suggest that these two Pelomedusid turtle species potentially compete in the freshwater habitats in the southern Ivory Coast.

Highlights

Studies of freshwater turtle communities have primarily focused on microhabitat resource partitioning [1,2,3,4]
Our results suggest that P. castaneus and P. cupulatta exhibit differences in three of the four spatial niche characteristics considered in our study, notably macro-habitat and, in the case of micro-habitat characteristics, bank type and type of aquatic vegetation
Our analysis indicates that habitat partitioning occurs in these two sympatric turtle species; this result is corroborated among three sympatric Pelomedusidae in seven study sites in southern Benin [4]

Summary

Introduction

Studies of freshwater turtle communities have primarily focused on microhabitat resource partitioning [1,2,3,4]. Some evidence suggests that spatial niche partitioning by turtles is, at least in part, determined by interspecific competition (see [5] for a metaanalysis of published research). Aggressive interactions, for instance, especially during basking, can result in competitive exclusion in some turtle assemblages [6,7]. Micro-habitat partitioning by sympatric turtle species, can reduce aggressive interactions and facilitate coexistence [5]. Regarding Africa, quantitative studies on whole freshwater turtle communities have been carried out in Nigeria [13,14,15] and Benin [4] or on selected species within a large geographic region [16]

Methods

Results

Conclusion