Christian Che-Castaldo

U.S. Geological Survey, Wisconsin Cooperative Wildlife Research Unit
Department of Forest and Wildlife Ecology, University of Wisconsin-Madison

Primary succession structures amphibian population dynamics


Amphibians play a crucial role in primary succession, as they efficiently transfer energy across trophic levels to bridge the gap between invertebrates and reptile and mammalian predators. While amphibian community assembly has been shown to be disturbance-mediated, we know little about how primary succession affects the demographics of its constituent members. Relying on detailed investigations of the natural history of amphibians colonizing the Mount St. Helens debris avalanche following the 1980 eruption, we use long-term monitoring data in conjunction with remote sensing to better understand how the geological impacts of the eruption and subsequent ecological recovery, alter amphibian species interactions, population dynamics, and community-level biodiversity.


Continental models of Pygoscelid penguin abundance


Colonial seabirds have long served as indicator species for the health of the Southern Ocean. Demographic data for these species are very sparse, and counts repeatedly collected at a small number of breeding sites are often used for the adaptive management of marine resources at very large spatial scales, even though their suitability for this purpose is unknown. To overcome this limitation, I have co-developed the Antarctic Penguin Biogeography Project, which collects and organizes all publicly available Antarctic penguin count data, while also building computer vision models to determine penguin colony size from Landsat imagery. Satellite imagery represents a crucial but underutilized tool for filling the large gaps in penguin abundance data, and I am developing statistical methods to integrate colony size from remote sensing into continental-scale penguin population models.

Stress-mediated herbivore phenology directs succession


Variation in plant quality across space and time is a driving force behind the distribution of herbivorous insects on their host plants. We used Bayesian dynamic site-occupancy models to better understand how host plant quality directs the herbivory dynamics of the poplar-willow weevil on Sitka willow, a dioecious pioneering shrub colonizing Mount St. Helens following the 1980 eruption. This work highlights the common, but often overlooked, phenological basis of the plant stress and plant vigor hypotheses, which both focus on how host plant stress changes the quality of resources available to immature insects. Insect-host phenology forestalls willow colonization of drier areas through host plant juvenilization by weevils, while having a small effect in riparian zones where willows tolerate herbivory. This seral delay has promoted alternative successional trajectories, such as the moss and herb dominated communities seen today on the Mount St. Helens pyroclastic flows.


Causes of female-biased adult sex ratios in willow


The mechanisms behind biased sex-ratios in dioecious plants are often not well understood and represent the product of genetic and ecological factors acting throughout the life of the plant. On Mount St. Helens, we observed a strong female-bias in Sitka willow genet populations, sex ratios that are consistent with those reported from other Salix populations worldwide. The causes of female-bias in Salix remains an open question, as females presumably pay higher reproductive costs than males and the lack of well-defined sex chromosomes precludes most genetic processes known to cause female-bias. To investiagte this, we measured whole-plant reproductive allocation and survival for male and female willows on Mount St. Helens, while experimentally creating artificial streams to test for sex-bias in the establishment of willows from stem fragments. These efforts have implicated early‐acting genetic factors as the cause for female-biased sex ratios, a hypothesis supported by recent molecular work.