HOW DENDRITIC ECOLOGICAL NETWORKS STRUCTURE THE DISTRIBUTION AND MOVEMENT OF STREAM SALAMANDERS

Abstract

Research in population biology is concerned with factors affecting the change in a population over time, including births, deaths, immigration and emigration. Despite the potential importance of dispersal, empirical data on movement are lacking in many systems. Hence, there is a large body of theory on dispersal that remains to be tested in real biological systems. In particular, many organisms exist in ecological networks with the complex geometry common to caves, plants and streams. This alternative network topology might influence population and community-level patterns and processes.

Chapter 1 introduces the concept of the "dendritic ecological network," highlighting special properties and characteristics useful for understanding community and population-level processes. Of most interest for this dissertation is how the rigid spatial structure and branching topology may have implications for patterns of population distribution and the evolution of movement behaviour in stream organisms.

In chapters 2 and 3, I investigate patterns of stream salamander distribution, which may be related to the spatial configuration of stream habitat branches. First, I determined the sampling methods suitable for estimating the probability a site is occupied by one of three stream salamander species. I then applied these methods to investigate occupancy patterns, in relation to stream spatial layout across two mid-Atlantic regions. I found that all three species have higher occupancy in streams with a confluent, firs-order stream, though the strength of this association seems to be related to life history characteristics.

Finally, in chapters 4 and 5, I sought to identify movement pathways for larval, juvenile and adult Desmognathus stream salamanders. First, I tested my marking method on larval individuals, and found that the visual implant elastomer marks can be retained through metamorphosis. Then, using individual mark-recapture and multistate modeling, I found that stream salamanders move during the juvenile stage, with both an upstream-biased movement, and a proportionally large probability of moving overland to an adjacent stream reach.

The chapters in this dissertation combine empirical investigations of the patterns and pathways of stream salamander movement. Taken together, they elucidate the underlying importance of dendritic ecological networks, and provide direct evidence of dispersal in stream salamanders.