Monitoring and Population Ecology

Due to the ubiquity of disease in natural systems, hosts have evolved strategies of disease resistance and tolerance to defend themselves from further harm once infected. Resistance strategies directly limit pathogen growth, typically leading to lower infection burdens in the host. A tolerance approach limits the fitness consequences caused by the pathogen but does not directly inhibit pathogen growth. Testing for intraspecific variation in wild host populations is important for informing conservation decisions about captive breeding, translocation, and disease treatment. Here, we test for the relative importance of tolerance and resistance in multiple populations of boreal toads (Anaxyrus boreas boreas) against Batrachochytrium dendrobatidis (Bd), the amphibian fungal pathogen responsible for the greatest host biodiversity loss due to disease. Boreal toads have severely declined in Colorado (CO) due to Bd, but toad populations challenged with Bd in western Wyoming (WY) appear to be less affected. We used a common garden infection experiment to expose post-metamorphic toads sourced from four populations (2 in CO and 2 in WY) to Bd and monitored changes in mass, pathogen burden, and survival for eight weeks. We used a multi-state modeling approach to estimate weekly survival and transition probabilities between infected and cleared states, reflecting a dynamic infection process that traditional approaches fail to capture. We found that WY boreal toads are highly tolerant to Bd infection with higher survival probabilities than those in CO when infected with identical pathogen burdens. WY toads also had higher probabilities of clearing infections and took an average of five days longer to reach peak infection burdens. Our results demonstrate strong intraspecific differences in tolerance and resistance that explain why population declines vary regionally across the species. We used a robust, multi-state framework to gain inference on typically hidden disease processes when testing for host tolerance or resistance and demonstrated that describing an entire species as ‘tolerant’ or ‘resistant’ is unwise without testing for intraspecific variation in host defenses.

This data release contains information collected during surveys for chorus fogs (Pseudacris maculata), wood frogs (Lithobates sylvaticus) and tiger salamanders (Ambystoma mavortium) conducted in Rocky Mountain National Park (1986 – 2022) by the U.S. Geological Survey. Survey methods included visual encounter and aural surveys, and dip netting. Data collected between 1986 and 1994 focused on named water bodies in Rocky Mountain National Park. Data collected between 1995 and 1999 are from focal monitoring sites as well as sporadic surveys of other wetlands. Data collected between 2000-2002 represent repeated surveys conducted between 1986 and 1994 (e.g., park-wide surveys of named water bodies) and additional surveys of unnamed waterbodies. Data collected after 2002 were collected under an occupancy framework. Sites were identified within pre-defined catchments using the National Wetlands Inventory Database to locate potential amphibian breeding habitat (e.g., ponds, ephemeral wetlands). If appropriate sites were encountered in the field and were not indicated on National Wetland Inventory databases (https://www.fws.gov/program/national-wetlands-inventory/metadata), they were added as incidental sites. Waterbodies were visited and surveyed at least two times during the amphibian active season (May and mid-August). Water bodies were surveyed for all life stages of amphibians.

Understanding the geographical range of a species is essential to successful conservation and management, but their ranges are not always fully known. Ringed Map Turtles, Graptemys oculifera, have been federally listed as a threatened species since 1986, and they have long been considered endemic to the Pearl River system of central Mississippi and southeastern Louisiana. By way of a 2021 citizen scientist observation, a new G. oculifera population was discovered in the Bogue Falaya, a river system that is west of and isolated from the Pearl River system. Genetic analyses of 23 individuals from the Bogue Falaya demonstrate their distinctiveness relative to sites in the Pearl River, suggesting it is a natural rather than introduced population. Therefore, G. oculifera should no longer be considered endemic to the Pearl River system, and this Bogue Falaya population of G. oculifera may warrant the designation of a distinct population segment under the Endangered Species Act. A thorough assessment of the distribution, abundance, and conservation threats to the Bogue Falaya population of G. oculifera is needed as well as surveys of surrounding systems. This discovery of a long federally protected species in the city limits of Covington, Louisiana, underscores the need for more surveys to fully understand species distributions and documents how citizen scientists can advance scientific knowledge.