conservation.arizona.edu - introduced species

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

Rushton, S. P., D. J. A. Wood, P. W. W. Lurz, and J. L. Koprowski. 2006. Modelling the population dynamics of the Mt. Graham red squirrel: Can we predict its future in a changing environment with multiple threats? Biological Conservation 131: 121-131.

thackerk1 — Tue, 30 Jul 2019 18:34:52 +0000

Authors

S.P. Rushton

D.J.A. Wood

P.W.W. Lurz

J.L. Koprowski

The Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis; MGRS) is among the most critically endangered mammals in the United States and is isolated on the periphery of the species’ range, potentially increasing its conservation priority. To investigate potential threats to the population and provide a tool for land managers, we developed a spatially explicit population dynamics model. We tested model predictions using available range-wide data from the literature and field work specific to the MGRS. A general model input data set using mean life history values overpredicted MGRS abundance. However, we found significant correlation with known squirrel abundance using a general data set with curtailed fecundity and survival. A model with MGRS-specific data provided the best fit to observed population size. We investigated potential impacts of two major threats to the MGRS: competition from introduced Abert’s squirrels (Sciurus aberti) and increased levels of predation. Predation and particularly competition could have significant effects on the future population of the MGRS. Careful attention must be used to model the viability of fringe populations as peripheral populations can have a different life history than populations found in the range core

Additional Information

Modelling the population dynamics of the Mt. Graham red squirrel: Can we predict its future in a changing environment with multi

Date of publication:

2006

Topics

conservation

Mount Graham Red Squirrel

introduced species

Abert’s squirrel

Merrick, M. J., J. L. Koprowski, and R. N. Gwinn. 2012. Sciurus stramineus (Rodentia: Sciuridae). Mammalian Species 44: 44-50

thackerk1 — Tue, 23 Jul 2019 23:31:56 +0000

Authors

Melissa J. Merrick

John L. Koprowski

R. Nathan Gwinn

Sciurus stramineus Eydoux and Souleyet, 1841, is a large-bodied squirrel commonly called the Guayaquil squirrel. S. stramineus is characterized by a distinct grizzled-gray pelage with dark feet and ears, a long tail, and a distinctive white ‘‘collar’’ behind the ears. It is native to the western slope of the Andes, occurring from dry or humid tropical forests at sea level to high- elevation montane forests up to 2,000 m in Ecuador and Peru. S. stramineus is adaptable, adjusting to anthropogenic changes and living close to human settlements, in coffee plantations, with an introduced population in Lima, Peru. Because of a tolerance for living in proximity to humans, S. stramineus is also a concern for transmission of diseases such as leptospirosis and Chagas disease.

Additional Information

Sciurus stramineus (Rodentia: Sciuridae)

Date of publication:

2012

Topics

Guayaquil squirrel

Ecuador

introduced species

tree squirrel

sciurid

Peru

Koprowski, J. L. 2005. Management and conservation of tree squirrels: The importance of endemism, species richness, and forest condition. USDA Forest Service Proceedings RMRS-P-36: 245-250.

thackerk1 — Mon, 22 Jul 2019 23:19:59 +0000

Authors

John L. Koprowski

Tree squirrels are excellent indicators of forest health yet the taxon is understudied. Most tree squirrels in the Holarctic Region are imperiled with some level of legal protection. The Madrean Archipelago is the epicenter for tree squirrel diversity in North America with 5 endemic species and 2 introduced species. Most species of the region are poorly studied in keeping with an international dearth of data on this taxon; 3 of the 5 native species are the subject of <3 publications. Herein, I review literature on the response of squirrels to forest management from clearcutting to less comprehensive operations. Major threats to squirrel diversity in the Madrean Archipelago’s Sky Islands are the introduction of species, altered fire regimes, and inappropriate application of forestry practices.

Additional Information

Management and Conservation of Tree Squirrels: The Importance of Endemism, Species Richness, and Forest Condition

Date of publication:

2005

Topics

forest health

tree squirrels

endemic species

introduced species

Madrean Archipelago’s Sky Islands

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.

Additional Information

Potential for Nest Site Competition between Native and Exotic Tree Squirrels

Date of publication:

2009

Topics

coexistence

introduced species

Mount Graham Red Squirrel

Abert’s squirrels

niche overlap

tassel-eared squirrel

pine squirrel