conservation.arizona.edu - diet

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.

Additional Information

Canadian Journal of Zoology

Date of publication:

2017

Topics

black bear

grizzly bear

grey wolf

caribou

predation

niche

diet

trophic relations

stable isotope analysis

Research Categories

Natural History Population Ecology Threatened and Endangered Species

Edelman, A. J. and J. L. Koprowski. 2005. Diet and tree use of Abert's squirrels (Sciurus aberti) in a mixed-conifer forest. The Southwestern Naturalist 50(4): 461-465.

thackerk1 — Thu, 27 Jun 2019 20:58:17 +0000

Authors

Andrew J. Edelman

John L. Koprowski

Abert’s squirrels (Sciurus aberti) are reported to be dependent on ponderosa pine (Pinus ponderosa) forests for food, cover, and nest sites. Introduced Abert’s squirrels in the Pinaleño Mountains of Arizona, however, occupy forests that contain little to no ponderosa pine. We documented diet and tree use of Abert’s squirrels in mixed-conifer forests of the Pinaleño Mountains using observations of marked animals. Individuals ate similar food items as Abert’s squirrels in ponderosa pine forests, including seeds, inner bark, buds, and fungi, but 5 conifer species were used as food sources. Douglas-fir (Pseudotsuga menziesii) and southwestern white pine (Pinus strob- iformis) were the most frequently eaten conifer species. Abert’s squirrels also were observed in all tree species. Our results suggest that the dependence of Abert’s squirrels on ponderosa pine is not as strong as previously reported.

Additional Information

DIET AND TREE USE OF ABERT'S SQUIRRELS (SCIURUS ABERTI) IN A MIXED-CONIFER FOREST

Date of publication:

2005

Topics

Abert’s squirrels

mixed-conifer forests

Pinaleño Mountains

diet

nest sites

Derbridge, J. J., P. R. Krausman, and C. T. Darimont. 2012. Using Bayesian stable isotope mixing models to estimate wolf diet ina multi-prey ecosystem. The Journal of Wildlife Managment 76:1277-1289.

thackerk1 — Tue, 25 Jun 2019 00:17:31 +0000

Authors

Jonathan J. Derbridge

Paul R. Krausman

Chris T. Darimont

Stable isotope analysis (SIA) of wolf (Canis lupus) tissues can be used to estimate diet and intra- population diet variability when potential prey have distinct d13C and d15N values. We tested this technique using guard hairs collected from 44 wolves in 12 northwestern Montana packs, summer 2009. We used hierarchical Bayesian stable isotope mixing models to determine diet and scales of diet variation fromd13C and d15N of wolves and potential prey, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), snowshoe hare (Lepus americanus), and other prey. As a check on SIA results, we conducted a separate diet analysis with temporally matched scats (i.e., collected in summer 2008) from 4 of the same packs. Wolves were centered on the ungulate prey in the isotope mixing space. Both methods revealed differences among pack diets and that wolves may consume moose in greater proportions than predicted by available biomass. Stable isotope analysis, and scat results were not entirely concordant; assumptions related to tissues of use in SIA, hair growth period in wolves, and scat sampling may have contributed to a mismatch between methods. Incorrect fractionation values, insufficient separation of prey in the isotope mixing space, choice of prior information in the Bayesian mixing models, and unexplained factors may have distorted diet estimates. However, the consistently high proportion of moose in pack diets suggests that increased population monitoring would benefit management of moose and wolves. Our results also support suggestions of other researchers that species-specific fractionation values should be used whenever possible, and that SIA may sometimes only provide indices of use for general groups of prey (e.g., large ungulates). © 2012 The Wildlife Society.

Additional Information

Using Bayesian stable isotope mixing models to estimate wolf diet in a multi‐prey ecosystem

Date of publication:

2012

Topics

wolf

diet

stable isotopes

fractionation

Montana

Bayesian

scat sampling

prey

white-tailed deer

moose

mule deer

elk

snowshoe hare

Derbridge, J. J., J. A. Merkle, M. E. Bucci, P. Callahan, J. L. Koprowski, J. L. Polfus, and P. R. Krausman. 2015. Experimentally derived δ13C and δ15N discrimination factors for gray wolves and the impact of prior information in Bayesian mixing models. P

thackerk1 — Tue, 25 Jun 2019 00:11:46 +0000

Authors

Jonathan J. Derbridge

Jerod A. Merkle

Melanie E. Bucci

Peggy Callahan

John L. Koprowski

Jean L. Polfus

Paul R. Krausman

Stable isotope analysis of diet has become a common tool in conservation research. However, the multiple sources of uncertainty inherent in this analysis framework involve consequences that have not been thoroughly addressed. Uncertainty arises from the choice of trophic discrimination factors, and for Bayesian stable isotope mixing models (SIMMs), the specification of prior information; the combined effect of these aspects has not been explicitly tested. We used a captive feeding study of gray wolves (Canis lupus) to determine the first experimentally-derived trophic discrimination factors of C and N for this large carnivore of broad conservation interest. Using the estimated diet in our controlled system and data from a published study on wild wolves and their prey in Montana, USA, we then investigated the simultaneous effect of discrimination factors and prior information on diet reconstruction with Bayesian SIMMs. Discrimination factors for gray wolves and their prey were 1.97‰ forδ13C and 3.04‰ for δ15N. Specifying wolf discrimination factors, as opposed to the commonly used red fox (Vulpes vulpes) factors, made little practical difference to estimates of wolf diet, but prior information had a strong effect on bias, precision, and accuracy of posterior estimates. Without specifying prior information in our Bayesian SIMM, it was not possible to produce SIMM posteriors statistically similar to the estimated diet in our controlled study or the diet of wild wolves. Our study demonstrates the critical effect of prior information on estimates of animal diets using Bayesian SIMMs, and suggests species-specific trophic discrimination factors are of secondary importance. When using stable isotope analysis to inform conservation decisions researchers should understand the limits of their data. It may be difficult to obtain useful information from SIMMs if informative priors are omitted and species-specific discrimination factors are unavailable.

Additional Information

Experimentally Derived δ13C and δ15N Discrimination Factors for Gray Wolves and the Impact of Prior Information in Bayesian Mixi

Date of publication:

2015

Topics

gray wolves

stable isotope analysis

large carnivore

diet

captive feeding study