Available at: https://digitalcommons.calpoly.edu/theses/3219
Date of Award
12-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Tim Bean
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
Distribution models provide a practical use case of connecting ecological niche theory with species’ occurrence and assemblages. By explicitly linking Hutchinson’s “niche space” with geographic space researchers can gain valuable information on a species’ niche characteristics and interactions, thereby informing conservation and management practices. The narrow-faced kangaroo rat (Dipodomys venustus) is a highly understudied kangaroo rat species endemic to the central coast of California and is an ideal species to explore niche theory in distribution modeling. Three subspecies are currently recognized: The Santa Cruz kangaroo rat (D. v. venustus), the elephant-eared kangaroo rat (D. v. elephantinus), and the Santa Lucia kangaroo rat (D. v. sanctiluciae). All three subspecies are on California Department of Fish and Wildlife’s “special animal list” and D. venustus venustus is considered critically imperiled – though this designation offers no formal protection. The narrow-faced kangaroo rat is an important member of its ecological communities as a prey source for many mesocarnivore, bird of prey, and snake species. It is also likely that they have engineering/keystone effects via seed caching and the creation of complex burrow systems. Before management action can be taken, more information is needed on population trends, associations with bioclimatic variables, and sub-species taxonomic status. I evaluated the current distribution, habitat associations, and niche overlap for the narrow-faced kangaroo rat and each of its subspecies across their entire range. I conducted camera and live trapping surveys to sample areas of both high and low habitat suitability. Each captured kangaroo rat was identified genetically to subspecies. I then created five ensemble species distribution models, two range-wide, and three subspecies models using the TidySDM package in program R by incorporating a suite of bioclimatic variables. I compared each model using Warren’s I to evaluate niche conservatism. These models helped reconcile unknowns in historical literature and provided a clearer picture of the distribution and niche for the species. The range-wide models predicted far less suitable habitat than previously assumed and a highly constrained niche. A large limiting factor in their niche was the strong relationship narrow-faced kangaroo rat presence has with manzanita at coarse spatial scales. This relationship was seen across all models, with the only exception being the elephant-eared kangaroo rat model which showed minimum annual temperature having equal importance to manzanita. There were moderate levels of niche overlap and unique variable response curves among models suggesting the subspecies exhibit some level of ecological distinction. Given the different variable responses in the subspecies models as well as the low to moderate levels of niche overlap, each subspecies would likely benefit from individual management plans. Additionally, the restricted range and habitat predicted by the models reinforces concerns of a vulnerable species. More research is needed to understand the mechanisms underlying the relationships seen in the models which will aid in conservation of the species going forward.