Occupancy trends in amphibians
Understanding the mechanisms underlying amphibian occupancy is critically important for meeting current management goals of the Wyoming Game and Fish Department, US Forest Service, and other agencies in the Rocky Mountain region. I am conducting trend analyses for the Rocky Mountain Amphibian Project (RMAP), a multi-agency and community science-driven monitoring program established to guide management of amphibians in Wyoming and northern Colorado. The program is impressive – including annual surveys (beginning in 2012) of 375 wetlands across 69 catchments. I have already completed analyses testing for differences in detection probabilities between community surveyors and trained biologists, helping to increase our understanding of the efficacy of citizen scientists for long-term monitoring efforts with complex study designs. I am currently working to develop hierarchical Bayesian models of occupancy for 6 amphibian species in order to test for underlying drivers, identify threats to persistence, and make management recommendations.
See Estes-Zumpf, Addis, et al. (2022). Ecological Indicators.
Understanding the mechanisms underlying amphibian occupancy is critically important for meeting current management goals of the Wyoming Game and Fish Department, US Forest Service, and other agencies in the Rocky Mountain region. I am conducting trend analyses for the Rocky Mountain Amphibian Project (RMAP), a multi-agency and community science-driven monitoring program established to guide management of amphibians in Wyoming and northern Colorado. The program is impressive – including annual surveys (beginning in 2012) of 375 wetlands across 69 catchments. I have already completed analyses testing for differences in detection probabilities between community surveyors and trained biologists, helping to increase our understanding of the efficacy of citizen scientists for long-term monitoring efforts with complex study designs. I am currently working to develop hierarchical Bayesian models of occupancy for 6 amphibian species in order to test for underlying drivers, identify threats to persistence, and make management recommendations.
See Estes-Zumpf, Addis, et al. (2022). Ecological Indicators.
Dispersal as a mechanism to reduce inbreeding risk
Dispersal distances should be important for mediating inbreeding risk because the likelihood of mating with relatives decreases with dispersal distance. However, empirical tests of this prediction are limited, particularly in the context of the multiple selective forces that can influence dispersal. Using the headwater stream salamander Gyrinophilus porphyriticus, we used capture-recapture and population genomic data to test whether spatial variation in environmental conditions leads to differences in dispersal distances, resulting in spatial variation in the effect of dispersal on inbreeding risk. We found that dispersal distances are greater in downstream reaches of headwater streams than in upstream reaches. Correspondingly, inbreeding risk was lower for dispersers in downstream reaches, but not in upstream reaches. These results show that environmentally associated variation in dispersal distances can cause the inbreeding consequences of dispersal to vary at fine spatial scales, and, importantly, that other selective pressures also contribute to phenotypic variation in dispersal distances in this system.
See Addis & Lowe (2022). The American Naturalist.
Local versus large-scale drivers of dispersal distance
Dispersal is expected to evolve as an adaptive mechanism to optimize individual fitness across the landscape. Decades of empirical work suggests that individuals use local habitat cues to make movement decisions, but theory predicts that dispersal can also evolve as a fixed trait, independent of local conditions, in environments characterized by a history of stochastic spatiotemporal variation. However, conditional and fixed models of dispersal evolution have primarily been evaluated using emigration data (stay vs. leave) and not dispersal distances. We used Gyrinophilus porphyriticus body condition as an index of local habitat quality, and G. porphyriticus survival probabilities as index of mortality risk resulting from the long-term history of environmental variation, to test whether conditional or fixed models of dispersal evolution predict variation in dispersal distance. We found that dispersal distance increased with declining survival probability, but was unrelated to spatial variation in body condition. These results suggest that salamanders do not base dispersal decision on local habitat quality, but variation in dispersal distances is instead a response to large-scale, long-term patterns of mortality risk. To our knowledge, this study provides the first empirical support for fixed models of dispersal evolution.
See Addis & Lowe (2020). Ecology.
Dispersal is expected to evolve as an adaptive mechanism to optimize individual fitness across the landscape. Decades of empirical work suggests that individuals use local habitat cues to make movement decisions, but theory predicts that dispersal can also evolve as a fixed trait, independent of local conditions, in environments characterized by a history of stochastic spatiotemporal variation. However, conditional and fixed models of dispersal evolution have primarily been evaluated using emigration data (stay vs. leave) and not dispersal distances. We used Gyrinophilus porphyriticus body condition as an index of local habitat quality, and G. porphyriticus survival probabilities as index of mortality risk resulting from the long-term history of environmental variation, to test whether conditional or fixed models of dispersal evolution predict variation in dispersal distance. We found that dispersal distance increased with declining survival probability, but was unrelated to spatial variation in body condition. These results suggest that salamanders do not base dispersal decision on local habitat quality, but variation in dispersal distances is instead a response to large-scale, long-term patterns of mortality risk. To our knowledge, this study provides the first empirical support for fixed models of dispersal evolution.
See Addis & Lowe (2020). Ecology.
Constraints on dispersal evolution
Across taxa, individuals vary in how far they disperse, with most individuals staying close to their origin, and far fewer individuals dispersing long distances. Despite their rarity, long-distance dispersal events contribute critically to range shifts, invasions, and population persistence. We used the stream salamander Gyrinophilus porphyriticus to investigate the causes and consequences of variation in dispersal distance. Using direct dispersal data from the field (via capture-mark-recapture surveys), we identified a morphological phenotype linked to variation in dispersal distance. Interestingly, this morphological specialization appears to come at a cost to individual swimming performance. Such trade-offs may help to explain the rarity of long-distance dispersers and provides mechanistic insight into proximate factors maintaining variation in dispersal distance in natural populations.
See Addis et al. (2019). Ecology and Evolution.
Across taxa, individuals vary in how far they disperse, with most individuals staying close to their origin, and far fewer individuals dispersing long distances. Despite their rarity, long-distance dispersal events contribute critically to range shifts, invasions, and population persistence. We used the stream salamander Gyrinophilus porphyriticus to investigate the causes and consequences of variation in dispersal distance. Using direct dispersal data from the field (via capture-mark-recapture surveys), we identified a morphological phenotype linked to variation in dispersal distance. Interestingly, this morphological specialization appears to come at a cost to individual swimming performance. Such trade-offs may help to explain the rarity of long-distance dispersers and provides mechanistic insight into proximate factors maintaining variation in dispersal distance in natural populations.
See Addis et al. (2019). Ecology and Evolution.
Population genetic structure and disease prevalence in boreal toads
Amphibians are more threatened than any other vertebrate class, in part because of life history characteristics that lead to patchy distributions and geographically isolated populations. Additionally, the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been linked to amphibian declines worldwide. My master’s research explored factors that influence population isolation, patterns of genetic variation, and disease prevalence in boreal toads, a species that is declining in portions of its range. I conducted this work in Glacier National Park, Montana, and found that mountain ridges are barriers to gene flow and that high elevation populations exhibited reduced genetic variation. Surprisingly, more heterozygous individuals were more likely to be infected with Bd, suggesting that dispersal may facilitate the spread of the disease.
See Addis et al. (2015). Conservation genetics.
Amphibians are more threatened than any other vertebrate class, in part because of life history characteristics that lead to patchy distributions and geographically isolated populations. Additionally, the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been linked to amphibian declines worldwide. My master’s research explored factors that influence population isolation, patterns of genetic variation, and disease prevalence in boreal toads, a species that is declining in portions of its range. I conducted this work in Glacier National Park, Montana, and found that mountain ridges are barriers to gene flow and that high elevation populations exhibited reduced genetic variation. Surprisingly, more heterozygous individuals were more likely to be infected with Bd, suggesting that dispersal may facilitate the spread of the disease.
See Addis et al. (2015). Conservation genetics.