Associations between glucocorticoids and habitat selection reflect daily and seasonal energy requirements.

BACKGROUND: Glucocorticoids are often associated with stressful environments, but they are also thought to drive the best strategies to improve fitness in stressful environments. Glucocorticoids improve fitness in part by regulating foraging behaviours in response to daily and seasonal energy requirements. However, many studies demonstrating relationships between foraging behaviour and glucocorticoids are experimental, and few observational studies conducted under natural conditions have tested whether changing glucocorticoid levels are related to daily and seasonal changes in energy requirements. METHODS: We integrated glucocorticoids into habitat selection models to test for relationships between foraging behaviour and glucocorticoid levels in elk (Cervus canadensis) as their daily and seasonal energy requirements changed. Using integrated step selection analysis, we tested whether elevated glucocorticoid levels were related to foraging habitat selection on a daily scale and whether that relationship became stronger during lactation, one of the greatest seasonal periods of energy requirement for female mammals. RESULTS: We found stronger selection of foraging habitat by female elk with elevated glucocorticoids (eß = 1.44 95% CI 1.01, 2.04). We found no difference in overall glucocorticoid levels after calving, nor a significant change in the relationship between glucocorticoids and foraging habitat selection at the time of calving. However, we found a gradual increase in the relationship between glucocorticoids and habitat selection by female elk as their calves grew over the next few months (eß = 1.01, 95% CI 1.00, 1.02), suggesting a potentially stronger physiological effect of glucocorticoids for elk with increasing energy requirements. CONCLUSIONS: We suggest glucocorticoid-integrated habitat selection models demonstrate the role of glucocorticoids in regulating foraging responses to daily and seasonal energy requirements. Ultimately, this integration will help elucidate the implications of elevated glucocorticoids under natural conditions.

Meta-analysis reveals between-population differences affect the link between glucocorticoids and population health.

Glucocorticoids are a popular tool for monitoring health of animal populations because they can increase with environmental stressors and can indicate chronic stress. However, individual responses to stressors create variation in the glucocorticoid-fitness relationship within populations. The inconsistency in this relationship calls into question the widespread use of glucocorticoids in conservation. We investigated the sources of variation in the glucocorticoid-fitness relationship by conducting a meta-analysis across a diverse set of species exposed to conservation-relevant stressors. We first quantified the extent to which studies inferred population health from glucocorticoids without first validating the glucocorticoid-fitness relationship in their own populations. We also tested whether population-level information like life history stage, sex and species longevity influenced the relationship between glucocorticoids and fitness. Finally, we tested for a universally consistent relationship between glucocorticoids and fitness across studies. We found more than half of peer-reviewed studies published between 2008 and 2022 inferred population health solely based on glucocorticoid levels. While life history stage explained some variation in the relationship between glucocorticoids and fitness, we found no consistent relationship between them. Much of the variation in the relationship could be the result of idiosyncratic characteristics of declining populations, such as unstable demographic structure, that coincided with large amounts of variation in glucocorticoid production. We suggest that conservation biologists capitalize on this variation in glucocorticoid production by declining populations by using the variance in glucocorticoid production as an early warning for declines in population health.

Bibliometric investigation of the integration of animal personality in conservation contexts.

Consistent individual differences in behavior, commonly termed animal personality, are a widespread phenomenon across taxa that have important consequences for fitness, natural selection, and trophic interactions. Animal personality research may prove useful in several conservation contexts, but which contexts remains to be determined. We conducted a structured literature review of 654 studies identified by combining search terms for animal personality and various conservation subfields. We scored the relevance of personality and conservation issues for each study to identify which studies meaningfully integrated the 2 fields as opposed to surface-level connections or vague allusions. We found a taxonomic bias toward mammals (29% of all studies). Very few amphibian or reptile studies applied personality research to conservation issues (6% each). Climate change (21%), invasive species (15%), and captive breeding and reintroduction (13%) were the most abundant conservation subfields that occurred in our search, though a substantial proportion of these papers weakly integrated conservation and animal personality (climate change 54%, invasive species 51%, captive breeding and reintroduction 40%). Based on our results, we recommend that researchers strive for consistent and broadly applicable terminology when describing consistent behavioral differences to minimize confusion and improve the searchability of research. We identify several gaps in the literature that appear to be promising and fruitful avenues for future research, such as disease transmission as a function of sociability or exploration as a driver of space use in protected areas. Practitioners can begin informing future conservation efforts with knowledge gained from animal personality research.

Investigación bibliométrica sobre la integración de la personalidad animal a los contextos de conservación Resumen Las diferencias individuales y constantes en el comportamiento, comúnmente llamadas personalidad animal, son un fenómeno generalizado en los taxones con consecuencias importantes para la aptitud, selección natural e interacciones tróficas. Las investigaciones sobre la personalidad animal pueden ser útiles en varios contextos de conservación, aunque falta determinar cuáles son estos contextos. Realizamos una revisión literaria estructurada de 654 estudios identificados mediante la combinación de los términos de búsqueda para la personalidad animal y varios subcampos de la conservación. Puntuamos la relevancia de la personalidad y los temas de conservación en cada estudio para identificar cuáles de estos integraron significativamente a ambos campos, contrario a las conexiones a nivel superficial o alusiones vagas. Descubrimos un sesgo taxonómico por los mamíferos (29% de todos los estudios). Pocos estudios enfocados en anfibios o reptiles aplicaron un estudio de personalidad a los temas de conservación (6% para cada uno). El cambio climático (21%), las especies invasoras (15%) y la reproducción en cautiverio y las reintroducciones (13%) fueron los subcampos de conservación más abundantes que aparecieron en nuestra búsqueda, aunque una proporción significativa de estos artículos integraron muy poco a la conservación y la personalidad animal (cambio climático 54%, especies invasoras 51%, reproducción en cautiverio y reintroducciones 40%). Con base en nuestros resultados, recomendamos que los investigadores procuren tener terminologías consistentes y de aplicación generalizada cuando describan las diferencias conductuales para así minimizar las confusiones y facilitar la búsqueda durante la investigación. Identificamos varios vacíos en la literatura que prometen ser vías fructíferas para las investigaciones en el futuro, como la transmisión de enfermedades como una función sociable o la exploración como un impulsor del uso del espacio en las áreas protegidas. Los practicantes pueden comenzar por guiar los siguientes esfuerzos de conservación con el conocimiento obtenido de las investigaciones sobre la personalidad animal.

Individual differences in habitat selection mediate landscape level predictions of a functional response.

Predicting future space use by animals requires models that consider both habitat availability and individual differences in habitat selection. The functional response in habitat selection posits animals adjust their habitat selection to availability, but population-level responses to availability may differ from individual responses. Generalized functional response (GFR) models account for functional responses by including fixed effect interactions between habitat availability and selection. Population-level resource selection functions instead account for individual selection responses to availability with random effects. We compared predictive performance of both approaches using a functional response in elk (Cervus canadensis) selection for mixed forest in response to road proximity, and avoidance of roads in response to mixed forest availability. We also investigated how performance changed when individuals responded differently to availability from the rest of the population. Individual variation in road avoidance decreased performance of both models (random effects: ß = 0.69, 95% CI 0.47, 0.91; GFR: ß = 0.38, 95% CI 0.05, 0.71). Changes in individual road and forest availability affected performance of neither model, suggesting individual responses to availability different from the functional response mediated performance. We also found that overall, both models performed similarly for predicting mixed forest selection (F1, 58 = 0.14, p = 0.71) and road avoidance (F1, 58 = 0.28, p = 0.60). GFR estimates were slightly better, but its larger number of covariates produced greater variance than the random effects model. Given this bias-variance trade-off, we conclude that neither model performs better for future space use predictions.

Burrowing Richardson's ground squirrels affect plant seedling assemblages via environmental but not seed bank changes.

In grassland ecosystems, burrowing mammals create disturbances, providing habitat for animal species and increasing plant community diversity. We investigated whether seedling assemblages on Richardson's ground squirrel Urocitellus richardsonii mounds result from seed rearrangement or environmental changes that favor germination of certain species over others. To test whether ground squirrels rearrange the seed bank by burrowing, we compared seed compositions among mounds, burrows, and undisturbed soil. To test whether ground squirrels change environmental conditions, we compared soil nitrate and bare ground cover on and off mounds. We also compared seedlings that germinated on mounds with seedlings that germinated on artificial disturbances from which we removed aboveground vegetation. Soil nitrate and bare ground cover were significantly higher on mounds than artificial disturbances. While seed richness and abundance did not differ among mounds, burrows, and undisturbed soil, seedling richness was reduced on mounds relative to artificial disturbances. Burrowing disturbance favors seedlings that can capitalize on bare ground availability but are less able to immobilize nitrate, as opposed to perennial species that immobilize more nitrate but take longer to establish. Our results suggest that Richardson's ground squirrels act as ecosystem engineers, although future research following succession on ground squirrel mounds is necessary to understand how they influence plant communities past the seedling stage.