Effects of Topology, Number and Location of Nodes, Population Density, and Stocking Duration on Hybrids’ Dispersal Across a Network

Scientific Disciplines
Biological Sciences - Aquatic
Montana State University
rainbow trout
Idaho State University
bozeman, montana
stream network
Baxter Idaho State University Department Biological Sciences Pocatello Idaho
Montana State University Department Land Resources Environmental Sciences PO Box
Robert E Gresswell Geological Survey
Department of Land Resources and Environmental Sciences
network topology
nonnative genes
spawning locations
spawning site
population density
stocking duration
stream network topology
Volume 16, No. 4

Effects of topology, number and location of nodes, 
population density, and stocking duration on hybrids’ 
dispersal across a network

Patrick Della Croce and Geoffrey C. Poole, Montana State University, Department of Land 
Resources and Environmental Sciences, P.O. Box 173120, Bozeman, Montana 59717-3120  patrick.
dellacroce@gmx.ch,  gpoole@montana.edu
Colden V. Baxter, Idaho State University, Department of Biological Sciences, Pocatello, Idaho 
83209 baxtcold@isu.edu
Robert E. Gresswell, U.S. Geological Survey, NoROCK,  2327 University Way, Suite 2, Bozeman, 
Montana 59715 bgresswell@usgs.gov
Hybridization between native cutthroat trout (Oncorhynchus clarki sp.) and introduced 
rainbow trout (O. mykiss) has been a topic of fisheries research for decades in the northern 
Rocky Mountains, USA. Several studies suggest that the likelihood of introgression at any 
location in a stream network is influenced by the distance between that location and the 
source of non-native genes, e.g., stocking locations or areas dominated by non-native or 
introgressed fish. The relationship between “distance to non-native source” and hybridization 
rates, however, is rarely quantified. Studies that attempt to quantify the relationship generally 
ignore the potential influence of stream network topology on gene movement. We have 
developed and applied an agent-based model that tracks the lineage and breeding location of 
individual fish over time, this simulating the movement of non-native genes among spawning 
locations within a stream network. The model considered both distances between spawning 
sites and network topology in determining non-natal spawning site selection by stocked and 
straying fish. Model results suggest that stream network topology has a strong influence on 
the relationship between “stream distance from genetic source” and “degree of hybridization” 
at spawning locations. However, the importance of topology varies depending on underlying 
model assumptions about, stocking duration, number and location of spawning grounds, 
population density, and spawning site fidelity, i.e., “straying rates,” within the river system.