River habitat homogenisation enhances trophic competition and promotes individual specialisation among young of the year fish

Abstract

In large rivers, fish ontogenic development success is mainly influenced by resource availability and by the possibility of species to adapt their diet (i.e. trophic niche). Humans have drastically modified freshwater habitats, notably for navigation purposes. Such modifications may reduce food availability for young of the year (YOY) fish and, consequently, influence their ability to reach the adult age. In the Meuse River, decrease of fish abundance is thought to be linked to a drastic reduction of phytoplankton biomass. In this context of decreasing phytoplankton biomass, we studied trophic niches of three cyprinid species (common bleak Alburnus alburnus, chub Squalius cephalus, and roach Rutilus rutilus) and one percid species (European perch Perca fluviatilis) at various stages of development, using stable isotope analysis in order to compare intra‐ and interspecific competition between sites differing in degree of channelisation. Two reaches of the Meuse River differing by their degree of regulation were investigated. We hypothesised that habitat homogenisation would (1) decrease food resource availability and diversity and (2) increase trophic competition, particularly among earlier ontogenic stages, and promote individual specialisation. Our study provides evidence that in the context of low planktonic biomass, most YOY relied on benthic food sources. Furthermore, the Meuse River flow and depth regulation significantly impacted the abundance and species richness of YOY. In the heavily channelised reach, between‐stages competition and low resource diversity lead to an increase in diet partitioning between cyprinid larvae, as well as consumption of non‐optimal energetic food sources such as aquatic vegetation by some individuals. By contrast, in the less channelised reach, larvae displayed a generalist feeding habit focusing on high energy content prey such as different taxa of macroinvertebrates, suggesting that the diversity of habitat reduces the food competition within and between stages. Intraspecific resource repartition is a key point for YOY fish having to cope with plankton‐depleted conditions. Younger cyprinid stages seem more affected by intra‐ and inter‐specific competition in the more channelised reach. YOY fish communities were also less diversified and abundant in the more altered site, which highlight the importance of limiting channelisation to better conserve fish communities.

Habitat complexity and individual variation in diet and morphology of a fish species associated with macrophytes

“…ecomorphological diversity, individual specialisation, macrophyte biomass, Moenkhausia forestii, nested diets niche variation hypothesis (Niche Hypothesis Variation), which suggests that niche expansion may occur due to variation in resource use among individuals of a single population. Thus, species considered generalists may be composed of specialist individuals that use a small subset of the entire niche of the population (Bolnick et al, 2003;Cobain, Steward, Trueman, & Jensen, 2019;Cunha, Wolff, & Hahn, 2018;Latli, Michel, Lepoint, & Kestemont, 2019).…”

A global horizon scan of the future impacts of robotics and autonomous systems on urban ecosystems

“…Education and citizen science (43) Leisure time increases (44) New employment opportunities in GI mm (45) Transport system and car ownership decreases (54) Wheel-less transport infrastructure (55) Built structure declines (56) Self-repairing built infrastructure (57) Ecosystem service mimicry (58) Pest and invasive species mm ( 64 . The full wording agreed by the participants for each opportunity is given in Supplementary Table 1.…”

“…Therefore, RAS may be unable to respond adequately to species population variation and phenology, or when species that are protected or of conservation concern are encountered. For hydrological systems in particular, participants noted that automated management could result in the homogenization of water currents and timings of flow, which are known to disrupt the lifecycles of flow-sensitive species 54 . Similarly, improved building maintenance could lead to the loss of nesting habitats and shelter (for example, for house sparrows Passer domesticus 55 ), especially for cavity and ground-nesting species.…”

“…53 Centre for Agri-Environmental Research, School of Agriculture, Policy and Development, University of Reading, Reading, UK. 54 School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, UK. 55 School of Geography, Earth and Environmental Sciences (GEES), University of Birmingham, Birmingham, UK.…”

Coupled fish-hydrogeomorphic responses to urbanization in streams of Columbus, Ohio, USA

“…Hydrologically unstable streams typically host fewer specialist species, with more habitat generalist and siltation-tolerant species [108]. Hydrogeomorphic instability driven by anthropogenic landscape alteration may favor some tolerant species that can better cope with rapid rates of environmental change [109], whereas species with more flexible feeding strategies (i.e., ability to switch food resources, even to nonoptimal sources) are best able to cope with varied food resource availability [110]. This may have been (among other causes) reflected in CCA relationships in which tolerant generalist species (e.g., Creek Chub) occurred in similar relative abundances across sites that displayed a range of hydrogeomorphic characteristics.…”