Microhabitat partitioning in seagrass mesograzers is driven by consistent species choices across multiple predator and competitor contexts

Abstract

Explanations for the coexistence of multiple species from the same functional group or taxonomic clade frequently include fine-scale resource partitioning. However, despite the hypothesized importance of niche partitioning, we know relatively little about the underlying mechanisms. For example, differences in resource use may be fixed consequences of organism traits, or they may be achieved via context-dependent behaviors. In this study we investigated mechanisms of microhabitat partitioning using eight species of marine mesograzers inhabiting seagrass and algae habitats, using laboratory trials to measure microhabitat use in the presence and absence of both predators and competitors. We found clear evidence for microhabitat partitioning between the species, which account for over 60% of the mesograzers commonly found in this system and vary in both body size and the ability to build tubes on habitat substrates. Species-specific microhabitat use was poorly predicted by these two traits, but remained remarkably consistent across contexts. Habitat use was not affected by the presence of fish predators common in this system, even though predation pressure is thought to place strong constraints on microhabitat in communities of plant-associated arthropods. The presence of competing species also did not affect the relative separation of microhabitat use. Behavioral responses to potential competitors did cause significant changes in microhabitat use in all of the smallest species, but these changes did not depend on competitor identity and were relatively small compared to among-species patterns of microhabitat partitioning. The consistency of species-specific microhabitat use, regardless of the presence of predators or competitors, should make coexistence most likely among species that differ in these choices. For these species, it appears that the benefits accrued from their selected microhabitats are not affected by species interactions, or that any benefits of alternative microhabitat use are outweighed by risks associated with movement.

Plant genotype identity and diversity interact with mesograzer species diversity to influence detrital consumption in eelgrass meadows

“…Although these experiments were conducted in lab where environmental context, flow, temperature and predator conditions, might differ from what would normally be experienced in the field, consistency across studies lead us to believe that the results may be robust. For example, the amphipods and isopods have robust habitat preference despite variation in predation risk (Lürig et al ), and the preferences we found for some genotypes over others match those found in other experiments conducted across years and nutrient conditions (Tomas et al ). Thus the basic mechanism likely underlying the consumer– plant diversity interaction (preference differences among grazers) seems consistent.…”

The role of plasticity in the evolution of cryptic pigmentation in a freshwater isopod

“…However, when fish were present, isopods densities were higher in mesocosms with macrophytes than in macrophyte‐free tanks, suggesting that macrophytes can reduce predation pressure by stickleback (Diehl & Kornijów, ). This could occur because macrophytes generate structural habitat complexity (Kovalenko et al., ; Lürig et al., ; Warfe, Barmuta, & Wotherspoon, ), making it difficult for fish to find and capture any isopods, or because they alter the intensity and heterogeneity of the light environment (Baker & Ball, ; Verweij et al., ).…”

“…However, it is also possible that both biotic and abiotic environmental differences can interact to affect the distributions of phenotypes and fitness, and their covariance. Macrophytes can generate structural complexity (Kovalenko, Thomaz, & Warfe, ) and affect background coloration (Tavares, Pestana, Rocha, Schiavone, & Guillermo‐Ferreira, ), to which not all prey phenotypes are equally well adapted (Lürig, Best, & Stachowicz, ). Thus, differences in macrophyte cover may affect the strength and direction of selection from predation (Merilaita, Lyytinen, & Mappes, ).…”

Multiple dimensions of intraspecific diversity affect biomass of eelgrass and its associated community

“…Several amphipods and isopods prefer different microhabitats within eelgrass beds at this site (Lürig et al. ), and the presence of genotypes with different heights, widths, or leaf traits may have influenced invertebrate biomass.…”