Reciprocated competition between two forest carnivores drives dietary specialization

Area of Science:

• Ecology
• Animal Behavior
• Wildlife Conservation

Background:

• Interspecific competition is a key driver of community structure, particularly among carnivores where body size influences dominance and interference competition.
• Exploitative competition, where subordinate species limit resources for dominant ones, is often overlooked in carnivore dynamics.
• Fishers (Pekania pennanti) and martens (Martes spp.) are related forest carnivores with overlapping diets and habitat use, differing significantly in body size, leading to strong interspecific competition.

Purpose of the Study:

• To investigate how interference and exploitative competition between fishers and martens affect their dietary niche overlap and foraging strategies.
• To understand the role of subordinate competitors in shaping the dietary niche of dominant competitors.
• To assess the influence of environmental factors on individual diet specialization in these two carnivore species.

Main Methods:

• Stable isotope analysis (δ13C and δ15N) of fisher and marten tissues to infer diet.
• Analysis of dietary items to quantify prey composition.
• Modeling of individual diet specialization in relation to competitor presence and environmental variables.

Main Results:

• High overlap was observed in the general isotopic niche (δ-space) of fishers and martens, but not in their core dietary proportions.
• When competitors were absent or rare, both species consumed more smaller-bodied prey.
• The dominant fisher shifted from specializing in larger prey to smaller prey when the subordinate marten was absent, demonstrating niche plasticity.
• Environmental factors like land cover diversity, prey abundance, and vegetation productivity influenced individual diet specialization.

Conclusions:

• Despite a clear dominance hierarchy, fishers demonstrate significant dietary flexibility in response to the presence of martens, highlighting the importance of exploitative competition.
• Subordinate competitors can exert considerable influence on the foraging behavior and dietary niche of dominant species.
• Understanding these complex competitive interactions is crucial for effective wildlife management and conservation of forest carnivore communities.