Population niche width is driven by within-individual niche expansion and individual specialization in introduced brook trout in mountain lakes

How individual variation shapes ecological niches in two Pipistrellus bat species

Niche partitioning is a crucial mechanism explaining species coexistence and biodiversity; however, the role of individual variation is less understood. As global changes reshuffle species communities, understanding coexistence mechanisms is vital. In this study, we use two co-occurring, morphologically similar bat species, Nathusius' pipistrelle (Pipistrellus nathusii) and the range-expanding Kuhl's pipistrelle (P. kuhlii), as models. We examine their niche partitioning across habitats and time, considering individual variations by analysing the spatio-temporal habitat selection of 58 radio-tracked individuals. For resource assessment, we use metabarcoding of guano samples. Our results show that individual variation in both species exceeded species-level differences. Nathusius' pipistrelle exhibits greater between-individual variation, while the range-expanding Kuhl's pipistrelle shows stronger within-individual variation, probably facilitating its expansion. This study emphasises the significance of individual variation in investigating animal niche partitioning. It suggests a contribution of within-individual variation in the range expansion of bat species, reshaping animal communities under global change.

Effects of Brook Trout Invasion on Behavioral and Dietary Shifts in Brown Trout

Behavioral variation within a population is generally maintained by frequency dependent selection, allowing various personalities to coexist. Bolder individuals usually engage in more risky behaviors that can gain fitness benefits such as growth under certain conditions. Therefore, it has been suggested that there should be a link between personality and dietary niches, but the results so far are inconsistent. In addition, the equilibrium of the distribution of behavioral traits and the trophic niche of native populations may shift following the introduction of an invasive species. Here, using the invasive brook trout (Salvelinus fontinalis) and native brown trout (Salmo trutta) as model species in two different natural streams in Sweden, we aimed to test whether (1) the trophic niche of native brown trout living in allopatry and brown trout living in sympatry with brook trout differ and (2) bolder brown trout individuals utilize a different foraging niche. Our results suggest that there is a dietary niche convergence between brown trout and brook trout, which likely is a result of brook trout invasion, but that the trophic niche of native brown trout varies across streams, possibly due to differing invasion impacts (varying ratio of brook trout to brown trout). We also found a strong positive correlation between trophic position and personality of brown trout irrespective of the presence of brook trout.

Trophic niche adaptation of mountain frogs around the Sichuan Basin: individual specialization and response to climate variations

BACKGROUND

Climatic and geographic variations have profound effects on the resource utilization of individuals and populations. Evaluating resource use in different environments is crucial for understanding species ecological adaptation strategies and promoting biodiversity conservation. Stable isotopes are widely used to assess trophic niches, providing quantitative indicators of ecological interactions between organisms and resource use in ecosystems. This study assesses the trophic niche traits of spiny-bellied frogs (Quasipaa boulengeri) in the marginal mountains of the Sichuan Basin in southwestern China using stable isotopes. Trophic niche variation under different time periods and environmental conditions is explored.

RESULTS

The spiny-bellied frogs experienced a significant reduction in trophic niche width during the past breeding season. The populations in the northwestern Sichuan Basin had a greater trophic niche width than the southeastern populations, and their δ15N values showed a positive correlation with temperature seasonality and a negative correlation with annual precipitation. Despite differences between the northwestern and southeastern populations, there was a consistent trend of increased individual specialization with latitude in both the northwestern and southeastern regions.

CONCLUSIONS

Ontogenetic niche shifts and differences in trophic niche traits between the northwestern and southeastern populations indicate diverse adaptation strategies in mountain frogs. The findings underscore the impact of geographical and climate variations on the resource utilization of amphibians. In addition, patterns of individual specialization highlight the significance of considering intra- and interpopulational changes when studying ecological adaptation.