nutcracker

Department of Zoology and Physiology

Program in Ecology

Evolutionary Biology

Biodiversity Institute

Contact information:

Office: Berry Center 149
Lab: Biological Sciences 439

Mailing Address:
Department of Zoology & Physiology, 3166
University of Wyoming
1000 E. University Ave.
Laramie, WY 82071

Office Ph: (307) 399-4785
Fax: (307) 766-5625
email


Research Interests

The role of coevolution in structuring and diversifying populations

Ecological speciation and mate choice in Cassia (South Hills) Crossbills

Climate change and causes of decline in crossbills

The influence of selection by a seed predator (red squirrels) in the driving spatial variation in serotiny

The ecology and evolution of seed dispersal in limber and whitebark pines


The role of coevolution in structuring and diversifying populations

Nearly 15 years ago we found evidence for coevolution between crossbills (Loxia) and lodgepole pine (Pinus contorta latifolia). Because it was so striking, we began examining other crossbill-conifer systems to (1) see how common coevolution is in the adaptive radition of crossbills and (2) determine the conditions that favor and disfavor coevolutionary arms races. This has taken us across North America, to Hispaniola and the Mediterranean, and most recently to Vietnam and the Philippines. We have found evidence for coevolution in most crossbill populations that we've studied and are beginning to understand the various factors that influence species interaction strength, including the presence and absence of preemptive competitors (tree squirrels), resource stability, and habitat area and structure, and how this alters the form and strength of phenotypic selection and coevolution. Here are our publications related to this research (many can be downloaded from my "publications" page). See CourseSource for a coevolution lesson plan based on the coevolutionary interactions between crossbills, squirrels and lodgepole pine.

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Ecological speciation and mate choice in Cassia Crossbills (formerly Type 9 or South Hills crossbill)

We have also examined how ecological adaptation as a result of divergent selection has led to reproductive isolation. The South Hills Crossbill - now recognized as a the Cassia Crossbill Loxia sinesciurus - has diverged not only in bill size (they are larger than other crossbills in the region) but also in calls and song. We have found extremely high levels of reproductive isolation between the Cassia Crossbill and the two Red Crossbill call types that breed in the South Hills. Much of the premating reproductive isolation is the result of Cassia Crossbills depressing seed availability so that other crossbills with smaller (less efficient) bills are unable to persist and breed. In addition, Cassia Crossbills preferentially pair with other Cassia Crossbills. Because Cassia Crossbills are so genetically divergent from other crossbills and levels of reproductive isolation are so high, it is now recognized as a species. Below are some publications related to ecological speciation and mate choice in Cassia Crossbills (some can be downloaded from my "publications" page). If you are interested in seeing the Cassia Crossbill, please visit this website for information and directions.

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Climate change and causes of decline in crossbills

The Cassia Crossbill declined by over 80 percent between 2003 and 2012. This decline is most likely the result of increasing numbers of hot summer days (>32 C), which are causing serotinous lodgepole pine cones to open and prematurely shed their seeds. We continue to study the decline and its causes using mark-recapture methods. Below are the two papers we have published on Cassia Crossbills, and a related one on European crossbills.

Mezquida, E. T., J-C. Svenning, R. W. Summers, and C. W. Benkman. 2018. Higher spring temperatures increase food scarcity and limit the current and future distributions of crossbills. Diversity and Distributions. In press.

Benkman, C. W. 2016. The natural history of the South Hills crossbill in relation to its impending extinction. American Naturalist 188:589-601.

Santisteban, L., C. W. Benkman, T. Fetz, and J. W. Smith. 2012. Survival and population size of a resident bird species are declining as temperature increases. Journal of Animal Ecology 81:352–363.

 

The influence of selection by a seed predator (red squirrels) on spatial variation in serotiny

Previous research on serotiny, a key life history trait for woody plants occurring in fire-prone habitats, has focused on fire where increasing fire frequency favors higher frequencies of serotiny. In contrast, we find that the dominant seed predator, the red squirrel, which harvests proportionately more serotinous than nonserotinous lodgepole pine cones, strongly selects against serotiny and can overwhelm selection from fire. Thus, the frequency of serotiny in lodgepole pine varies across the landscape depending on both fire frequency and the density of red squirrels. Based on our most recent work, the latter seems to be influenced by features of the soil and in turn forest structure and likely fungi abundance. This is of considerable interest as the frequency of serotiny influences the number of seeds in the canopy seed bank and the number of seedlings following a fire with community and ecosystem effects. See A Small Mammal With Outsized Impact, a post of our blog on this topic.

Benkman, C. W., S. Jech, and M. V. Talluto. 2016. From the ground up: Biotic and abiotic features that set the course from genes to ecosystems. Ecology and Evolution 6:7032-7038.

Talluto, M. V., and C. W. Benkman. 2014. Conflicting selection from fire and seed predation drives fine-scaled phenotypic variation in a widespread North American conifer. Proceedings of the National Academy of Sciences USA 111:9543-9548.

Talluto, M. V., and C. W. Benkman. 2013. Landscape-scale eco-evolutionary dynamics: selection by seed predators and fire determine a major reproductive strategy. Ecology 94:1307-1316.

Parchman, T. L., Z. Gompert, J. Mudge, F. D. Schilkey, C. W. Benkman, and C. A. Buerkle. 2012. Genome-wide association genetics of an adaptive trait in lodgepole pine. Molecular Ecology 21:2991-3005.

Benkman, C. W., A. M. Siepielski, and J. W. Smith. 2012. Consequences of trait evolution in a multi-species system. Pages 278-292 in Interaction Richness and Complexity: Ecological and Evolutionary Aspects of Trait-Mediated Indirect Interactions. T. Ohgushi, O. Schmitz, and R. Holt, eds. Cambridge University Press.

Benkman, C. W., and A. M. Siepielski. 2004. A keystone selective agent? Pine squirrels and the frequency of serotiny in lodgepole pine. Ecology 85:2082-2087.

 

The ecology and evolution of seed dispersal in limber and whitebark pines

Our interest is in understanding how the presence and absence of a superior preemptive competitor (pine squirrels Tamiasciurus) has affected the evolution of seed dispersal by Clark's Nutcrackers (Nucifraga columbiana) in limber pine (Pinus flexilis) and whitebark pine (P. albicaulis) and how this affects the ecology of the pines. Below are our publications related to this research.