Research

Andrew J. Edelman, Ph.D.
Department of Zoology and Physiology

University of Wyoming

Home	Research	Publications	Statistical Tools	Curriculum vitae

Network diagram and graphics layout by Elizabeth Rahel. Dancing manakins from a painting by Julie Zickefoose.	Current Research I am an NSF Bioinformatics Postdoctoral Fellow in the McDonald Lab at the Dept. of Zoology and Physiology, University of Wyoming. Currently, I am studying the temporal and spatial dynamics of cooperation in male social networks of long-tailed manakins (Chiroxiphia linearis). Long-tailed manakins are a unique tropical bird species in which males cooperatively display at leks to attract females. Males at leks maintain orderly queues where rank depends on age and social status. Dr. McDonald and I are seeking to understand how habitat structure and other factors affect the connectivity of manakin social networks. View video of long-tailed manakin dance here.
	Past Research
Banner-tailed kangaroo rat Banner-tailed kangaroo rat mound Rough harvester ant colony	Sex-specific proximal cues of natal dispersal in mammals The effects of proximal cues in eliciting natal dispersal are predicted to vary between sexes because of differences in reproductive strategies. To compare the proximal causes of natal dispersal in males and females, I experimentally manipulated resources of banner-tailed kangaroo rats (Dipodomys spectabilis), a species lacking sex-biased dispersal. I provided additional food to a subset of mothers and dependent offspring from lactation through natal dispersal. All supplemented offspring, regardless of sex, grew faster, were in better condition, and had higher survivorship than unsupplemented offspring. Resource supplementation only affected the timing of natal dispersal in males. Sons who received food supplements dispersed earlier than unsupplemented sons indicating that timing of dispersal was related to size and condition. Timing of dispersal in daughters was unaffected by resource supplementation suggesting that size and condition are less important proximal cues. These sex-specific responses to resources match the intersexual differences in mammalian reproductive strategies and parental investment patterns. My results support the hypothesis that sons remain at the natal site until a certain threshold of size and condition is reached. Male reproductive success is strongly dependent on body size, which affects their ability to find and defend mates. By allowing sons to remain at the natal site until this threshold is attained, mothers likely increase the fitness of their sons. Female reproductive success is influenced more by securing resources than body size. Thus, dispersing as early as developmentally feasible would allow daughters to secure an existing burrow system and begin caching food for future reproduction.
	Facilitative interactions between granivore groups (with E. Tuttle) In the Chihuahuan Desert, both rodents and harvester ants depend on the abundant seeds of annual plants. Rodents are hypothesized to enhance harvester ant populations through facilitation of small-seeded annuals on which ants feed. We used a novel, spatially-explicit approach to determine whether a positive interaction exists between the dominant species of these groups, banner-tailed kangaroo rats and rough harvester ants (Pogonomyrmex rugosus). We mapped the centers of activity for both species, kangaroo rat mounds and harvester ant colonies, as well as monitored extinction and founding of ant colonies. We also quantified resource abundance and foraging behavior for harvester ants with respect to distance from kangaroo rat mounds. We tested for a scale-dependent positive interaction by fitting spatial point process models to locations of mounds and colonies. In addition, we built logistic models of colony extinction risk that included neighborhood effects of mounds and tested their ability to predict spatial patterns of surviving colonies. Best-fitting spatial models exhibited small-scale aggregation (< 10 m) between kangaroo rat mounds and both established and newly-founded colonies resulting from a positive interspecific interaction. Extinction risk of vulnerable, newly-founded colonies was lower when located close to a mound and a logistic model containing distance to a mound predicted spatial structure of surviving colonies better than a random model. Seed abundance was greater and foraging time was shorter for colonies near mounds than for those farther away. Our combined results strongly support localized facilitation of harvester ants by kangaroo rats, mediated through secondary plant species. The scale-dependent effect of kangaroo rats on resource abundance and foraging costs appears to result in greater survivorship of young colonies near mounds.
Rattlesnake in mound
	Ecosystem engineering effects of kangaroo rats on species diversity In collaboration with Sevilleta REU undergraduates, Shawn Whiteman and Scott Johnson, we examined the ecosystem engineering effects of kangaroo rats on grassland faunal diversity. During Summer 2006 and 2007, these students observed the effect of mound occupancy on reptile and invertebrate fauna. Our results indicate that diversity of these organisms is higher on occupied than unoccupied mounds.

Abert’s squirrel Mt. Graham red squirrel	Behavior and ecology of invasive Abert's squirrels and their potential impact on the endangered Mt. Graham red squirrel From 2001-2003, I examined the social behavior and ecology of introduced Abert's squirrels (Sciurus aberti) in mixed-conifer forests of the Pinaleño Mountains, Arizona. This research was conducted as part of my M.S. degree at the University of Arizona under the advisorship of John Koprowski. Abert's squirrels are generally considered obligates of ponderosa pine forests. However, Abert's squirrels in the Pinaleños, unlike natural populations, use forests that contain almost no ponderosa pine. I studied the communal nesting, space use, nest use, and diet of Abert's squirrels in this unique locale. Abert’s squirrels are considered solitary, but I found that this species engages in group nesting throughout much of the year. Frequency of social contact is closely tied to ambient temperature and breeding status. I observed that Abert's squirrels used food and nest resources from many conifer species indicating that this squirrel species is not strictly dependent on ponderosa pine as previously believed. We also used these data to examine the potential for interspecific competition between introduced Abert's squirrels and endangered Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis). Our research shows that there is overlap in microhabitat characteristics, diet, and space between these species indicating that interspecific competition is likely. For complete details on this research, please download our manuscripts located on the publications page.
	Influence of female-biased sexual size dimorphism on dominance of female Townsend’s chipmunks During 1998-1999, I studied the effect of female-biased sexual size dimorphism (SSD) on the dominance of female Townsend's chipmunks (Tamias townsendii). This research was part of my senior thesis while I was an undergraduate at Willamette University. In many chipmunk species, females are 5-10% larger than males. I observed that female-biased SSD appears to allow larger females to dominate smaller males and females in laboratory encounters. For complete details of this research please download the reprint of our manuscript.