Experimental removals reveal dietary niche partitioning facilitates coexistence between native and introduced species

mmerrick — Fri, 12 Jun 2020 18:49:10 +0000

Authors

Jonathan J. Derbridge

John L. Koprowski

1. Niche overlap between native species and ecologically similar invaders can lead to
competitive exclusion of threatened native species, but if two such species also
co‐occur naturally elsewhere, interactions between native and introduced populations
may mirror coevolved niche partitioning that reduces competition and promotes
coexistence.
2. A single, insular population of Fremont’s squirrel (Tamiasciurus fremonti) the Mount
Graham red squirrel (MGRS; T. f. grahamensis) in the Pinaleño Mountains, Arizona,
USA, is critically endangered and resource competition with introduced Abert’s
squirrels (Sciurus aberti) may threaten its long‐term persistence. The species are
naturally synoptic in other mountain sites, and both consume diets comprised primarily
of conifer seeds and fungi.
3. We conducted experimental removals of introduced Abert’s squirrels and used
stable isotope analysis of diets before and after removals, and of diets in naturally
syntopic populations to test the hypothesis that dietary niche partitioning can
facilitate coexistence between native and introduced species. We also developed
a novel approach to determine the influence of fluctuating food availability on
carbon enrichment in consumers.
4. Mount Graham red squirrels and introduced Abert’s squirrels partitioned the dietary
niche similarly to naturally syntopic populations. Removals had no apparent
effect. Diet of MGRS was more closely linked to availability of resources than to
presence of Abert’s squirrels.
5. Flexible dietary niche of introduced Abert’s squirrels may have allowed them to
exploit a resource opportunity in syntopy with MGRS. Variable food production of
MGRS habitat may intensify competition in poor years, and territorial defense
against non‐native Abert’s squirrels likely imposes fitness costs on individual
MGRS. Similarity in our model species’ diets may make MGRS more vulnerable to
competition if climate change eliminates the advantages of larder‐hoarding.
Where introduced populations of ecologically similar species are better adapted

Additional Information

Ecology and Evolution

Date of publication:

2019

Topics

coexistence

diet

introduced species

niche

wildlife ecology

Research Categories

Behavioral Ecology Invasive Species Sky Islands Threatened and Endangered Species

Dietary niche partitioning among black bears, grizzly bears, and wolves in a multiprey ecosystem

thackerk1 — Tue, 23 Jul 2019 22:56:14 +0000

Authors

Jerod A. Merkle

Jean L. Polfus

Jonathan J. Debridge

Kimberly S. Heinemyer

Identifying mechanisms that promote coexistence of sympatric species is important for predicting ecological effects of anthropogenic change. Many caribou (Rangifer tarandus (L., 1758)) populations are declining, and it is unclear to what extent sympatric predators consume caribou or how alternative prey affect caribou–predator relationships. We used stable isotope mixing models to estimate diets of black bear (Ursus americanus Pallas, 1780), grizzly bear (Ursus arctos L., 1758), and grey wolves (Canis lupus L., 1758) during early, middle, and late summer of 2009–2010 in northwestern British Columbia, Canada. Although we expected wolf diet to be primarily composed of moose (Alces alces (L., 1758)) — as they exist at twice the density of caribou — wolf diet consisted principally of caribou, and to a lesser extent moose and beaver (Castor canadensis Kuhl, 1820), with little change occurring throughout summer. Black bear diet consisted mainly of vegetation and moose, shifting from moose to vegetation through summer. Grizzly bear diet consisted primarily of vegetation and moose, and did not change throughout summer. Our results demonstrate the role of dietary niche partitioning in bear and wolf coexistence, and that caribou may be primary prey for wolves in an ecosystem with relatively high moose abundance and low human development.