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

Edelman, A. J., J. L. Koprowski, and S. R. Bertelsen. 2009. Potential for nest site competition between native and exotic tree squirrels. Journal of Mammalogy 90: 167-174.

thackerk1 — Tue, 25 Jun 2019 00:54:50 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Sadie R. Bertelsen

In communities where strong interspecific competition between native species is lacking, exotic and native species often exhibit intense resource competition resulting in decline of native populations. We examined the potential for interspecific competition for nest sites between co-occurring native Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis) and exotic Abert’s squirrels (Sciurus aberti) in the Pinaleño Mountains of Arizona. Comparison of nest use between red and Abert’s squirrels at different scales (nest, nest tree, and nest site) revealed contrasting results. Competition for nests and nest trees appears unlikely given the dissimilarity in use of nest types and tree characteristics. Abert’s squirrels predominately used dreys, whereas red squirrels mostly used cavity nests. Neither squirrel species occupied a nest used by the other species. Nest trees differed in size and species between squirrels for dreys, but not for cavities. Abert’s squirrel nest sites were found in a wider range of microhabitats including almost all microhabitats in which red squirrel nest sites were located. Although there was significant overlap, each species showed distinct trends in microhabitat. In general, red squirrel nest sites were characterized as more densely forested areas dominated by corkbark fir (Abies lasiocarpa var.arizonica), whereas Abert’s squirrel nest sites were more open and contained greater tree species diversity. Overlap in microhabitat characteristics increases the likelihood of interspecific competition and could increase the vulnerability of red squirrels to extinction.