Phenotypically similar but ecologically distinct: differences in competitive ability and predation risk among amphipods

Abstract

Nature is often more diverse than expected with multiple species appearing to occupy the same niche. This observation is especially perplexing when the co‐occurring species are cryptic (i.e. only distinguishable via molecular markers), because phenotypic similarity is expected to correspond with strong niche overlap. One way that phenotypically similar species can coexist is if fine‐scale phenotypic differences affect how species interact with other members of the community that ultimately results in performance tradeoffs. An alternative explanation for co‐occurrence is that phenotypic similarity leads to ecological equivalence allowing species to co‐occur for long periods. We tested whether three phenotypically similar amphipod species that co‐occur exhibit performance tradeoffs that may allow them to stably coexist in lakes. We found that despite their similarity the three species differed in how well they performed in competition with each other and their ability to avoid predation by fish and invertebrate predators. In some species comparisons, performance tradeoffs were apparent with species that perform well against heterospecifics performing poorly against predators and vice versa. We also found evidence for direct antagonistic interactions among amphipod species, in the form of wounding, which may play a role in structuring amphipod assemblages. Finally, the two species with the most similar phenotypes showed comparable responses to competitors and predators, which suggests that long‐term co‐occurrence via ecological equivalence may also be important in this system. Collectively, our results suggest that a mix of performance tradeoffs and ecological equivalence may allow for higher diversity than expected in amphipod assemblages.

Proteogenomic insights into the core-proteome of female reproductive tissues from crustacean amphipods

“…species with similar morphological traits but genetic divergence. Several studies investigating the underlying mechanisms leading to cryptic phenomena have been carried out within the H. azteca complex [12], the G. fossarum/ pulex complex [13] and the M. plumulosa complex [14]. Finally, amphipods are also biological models in parasitology.…”

Overlapping trophic niches among co‐occurring amphipods from a cryptic species complex

“…Wellborn and Cothran (2007) reported such a situation within small lakes in the United States. Even though overlap was also observed among some species, this spatial distribution was concordant with a trade-off between the predation risks and the competitive ability of the species (Cothran et al, 2013;Wellborn & Cothran, 2007). Even though overlap was also observed among some species, this spatial distribution was concordant with a trade-off between the predation risks and the competitive ability of the species (Cothran et al, 2013;Wellborn & Cothran, 2007).…”

“…Apparently, amphipods from the complex can satisfy their nutritional needs on a variety of food sources (Dionne, 2009;Dionne et al, 2016;Hargrave, 1970 (Gause, 1934;Hardin, 1960). Because the morphological similarity of H. azteca species probably lowers the fitness differences (Cothran et al, 2013;Smith, 2013), species exclusion could be difficult because it takes more time to happen than the duration of resource limitations, allowing H. azteca species to co-occur during the openwater season. Because the morphological similarity of H. azteca species probably lowers the fitness differences (Cothran et al, 2013;Smith, 2013), species exclusion could be difficult because it takes more time to happen than the duration of resource limitations, allowing H. azteca species to co-occur during the openwater season.…”

“…On the other hand, other factors might limit the abundance of each species before the abundant food sources become limiting. Finally, even if ecological differences were found among them (Cothran et al, 2013;Wellborn & Cothran, 2007), H. azteca species could be close enough ecologically to allow their co-occurrence for an indefinite period. This may be especially true for H. azteca amphipods since, despite differences in predation risks among species, they are eaten in great number by fish and/or insect predators (Cothran, Noyes, & Relyea, 2015;Wellborn, 1995).…”

“…One possible explanation for the coexistence of such similar species could be the existence of a trade-off that would allow each species to spatially distribute within lakes according to their competitive ability and their ability to evade predators (Wellborn & Cothran, 2007). Experiments have shown that some species of the complex are more vulnerable to fish and invertebrates predators, and some species are better competitors when feeding on a single food resource (Cothran, Henderson, Schmidenberg, & Relyea, 2013;Smith, 2013). However, H. azteca species sometimes exhibit a high overlap in their habitat use, suggesting at least an overlap in some aspects of their ecological niches (Dionne et al, 2011;Smith, 2013).…”