Coexistence of predatory caddisfly species may be facilitated by variations in the morphology of feeding apparatus and diet

Abstract

The hypothesis of community‐wide character displacement (CWCD) predicts that coexisting species in the same guild should differ in morphological traits associated with resource acquisition, such that interspecific competition is unlikely. Hypothesis tests often focus on trophic structures involved in food acquisition, because variations in the morphology of foraging apparatus and diet composition may be directly related. Empirical evidence of such associations among sympatric guild members is, however, uncommon. The predatory larvae of caddisflies in the family Hydrobiosidae are ideal for studies of CWCD because the morphology of the prehensile foreleg, used to capture prey, varies markedly among genera. Further, hydrobiosids typically occur as species‐rich guilds, often with 10–20 species in a single community. Although the larvae are known to be predatory, detailed information on the diet of coexisting species is scarce. This study tested whether larval diet varied among multiple, sympatric species of hydrobiosid caddisflies that differed in foreleg morphology. Larval specimens were collected in summer and primarily from one river in central Victoria, Australia. Gut contents of late instar larvae were examined to describe diet composition, and diet was compared among taxa using measures of diet breadth and overlap. Seven sympatric species from six genera that differed in foreleg morphology were collected and late instar larvae were exclusively carnivorous. Diet composition and breadth varied markedly among some species, and diet was associated with morphology of the prehensile foreleg. Specialist predator species consumed predominantly chironomids and had high diet overlap. Generalists consumed primarily chironomids and mayflies, but overlap varied depending upon the preferred mayfly family and representation of other prey items, such as blackflies and insect eggs. All predator species consumed some caseless caddisflies and intraguild predation was strong in at least one species. The marked differences in diet and foreleg morphology among hydrobiosid species are consistent with the notion that CWCD influences guild membership and may facilitate species coexistence within guilds that are typically species‐rich. Although rarely considered for freshwater communities, CWCD may help explain species membership within other guilds. The magnitude of diet variations among genera within this family are more usually found across multiple families or orders, demonstrating that assumptions about the diet of even closely related taxa may be erroneous.

Hydrological controls on oviposition habitat are associated with egg‐laying phenology of some caddisflies

“…Alternatively, species coexistence may be related to temporal variations in recruitment pulses and, hence, variation in the occurrence of similar larval instars and, thus, partitioning of larval resources. This is theoretically possible for the Hydrobiosidae, whose larvae form a guild of free‐roaming predators and species can differ in diet composition (Lancaster, 2021). Multiple species of hydrobiosid commonly co‐occur in some rivers (Collier et al., 1995; Lancaster, 2021).…”

“…This is theoretically possible for the Hydrobiosidae, whose larvae form a guild of free‐roaming predators and species can differ in diet composition (Lancaster, 2021). Multiple species of hydrobiosid commonly co‐occur in some rivers (Collier et al., 1995; Lancaster, 2021). Coexistence in these guilds may lie in temporal partitioning of prey resources that arises through variations in oviposition phenology and larval development.…”

Characteristics and consequences of a disease outbreak in aquatic insects

“…Changes in community dynamics resulting from reduced abundances or altered relative abundances of caddisfly larvae may arise through shifts in trophic and competitive interactions. Hydrobiosid species are carnivorous, feeding primarily on primarily smaller aquatic invertebrates such as chironomids and mayflies, and exhibit intraguild predation (Lancaster, 2020). Reduced abundances as a consequence of infection could have cascading effects on these prey species.…”

“…Reduced abundances as a consequence of infection could have cascading effects on these prey species. Diet overlap varies between members of the group (Lancaster, 2020) and so the shifts in relative abundance that may arise from species‐specific infections provide opportunity for shifting competitive interactions through resource consumption or intraguild predation. Less is known about their predators, but reduced abundances could reduce food supply for in‐stream predators such as larger insect larvae and fish (Rees et al., 2020), while flying adults contribute subsidies to the diets of terrestrial predators (Clarke‐Wood, 2019).…”