Conservation Research Laboratory: General Conservation Projects

Allie Burnett

The Evolution of Alarm Calls in a Solitary Ground Squirrel, Ammospermophilus harrisii
  • Time Period: Fall 2016 -Present

  • Location: Santa Rita Experimental Range, Pima County AZ, U.S.A.

Background: Communication plays a monumental role in ecological interactions, functioning as a way to share information through signal variation. A majority of recent research has focused on the role of sociality in selecting for communication with multiple layers of variability, or communicative complexity. As social complexity increases, the need to communicate information to multiple individuals in a variety of contexts also increases. In support of this hypothesis, comparative analyses in ground-dwelling sciurids have shown that species exhibiting high social complexity do indeed exhibit high communicative complexity in alarm calling systems. These relationships, however, are less clearly defined in species of low to moderate sociality and there is some indication that other factors influence alarm call complexity. If some level of communicative complexity is found in a species of low sociality, it will serve as evidence that signal flexibility can precede and potentially initiate social evolution. By examining which, if any, elements of communicative complexity are maintained in an asocial species, it is possible to discern the importance of other causal factors, such as predation pressure, in the evolution of communicative complexity. Ammospermophilus harrisii is a small, diurnal ground squirrel that lives in low population densities. Offspring disperse soon after emergence above ground and because adults do not hibernate, individuals are solitary for a majority of the year. According to the sociality hypothesis, this species should exhibit little to no communicative complexity. Despite this, there is evidence of two types of calls given when disturbed, a surprising layer of complexity for an asocial animal that spends much of its life in solitude.

 I will be focusing on a population within the Santa Rita Experimental Range that occupies a transition zone between desert scrubland and grassland and has experienced extensive mesquite encroachment over the past century. By documenting differences in vegetation density among territories, I will assess potential effects of vegetation density on anti-predatory behavior and signal degradation. This has broad implications regarding the impacts of woody encroachment on predator-prey dynamics and communication in arid lands. The results of this study may be used to inform conservation strategies for threatened and endangered grassland species.

Research questions: 1) What is the function of these different alarm call types? 2) Does sociality play a role in selection for different call types in this population? 3) What other factors might contribute to this signal variation? To answer these questions, I will be eliciting anti-predatory behavior in A. harrisii via simulated predator introductions and comparing response behavior and acoustical characteristics across different social and predatory contexts.