Predator defense along a permanence gradient: roles of case structure, behavior, and developmental phenology in caddisflies

Abstract

Species replacements along freshwater permanence gradients are well documented, but underlying mechanisms are poorly understood for most taxa. In subalpine wetlands in Colorado, the relative abundance of caddisfly larvae shifts from temporary to permanent basins. Predators on caddisflies also shift along this gradient; salamanders (Ambystoma tigrinum nebulosum) in permanent ponds are replaced by predaceous diving beetles (Dytiscus dauricus) in temporary habitats. We conducted laboratory and field experiments to determine the effectiveness of caddisfly cases in reducing vulnerability to these predators. We found that larvae of a temporary-habitat caddisfly (Asynarchus nigriculus) were the most vulnerable to salamanders. Two relatively invulnerable species (Limnephilus externus, L. picturatus) exhibited behaviors that reduced the likelihood of detection and attack, whereas the least vulnerable species (Agrypnia deflata) was frequently detected and attacked, but rarely captured because cases provided an effective refuge. Vulnerability to beetle predation was also affected by cases. The stout cases of L. externus larvae frequently deterred beetle larvae, whereas the tubular cases of the other species were relatively ineffective. Two of these vulnerable species (A. nigriculus and L. picturatus) often co-occur with beetles; thus, case construction alone is insufficient to explain patterns of caddisfly coexistence along the permanence gradient. One explanation for the coexistence of these two species with beetles is that they develop rapidly during early summer and pupate before beetle larvae become abundant. One species (L. picturatus) pupates by burying into soft substrates that serve as a refuge. The other (A. nigriculus) builds stone pupal cases, which in field experiments, more than doubles survival compared to organic pupal cases. The combined results of these experiments suggest that caddisfly distributions along permanence gradients depend on a suite of primary and secondary predator defenses that include larval and pupal case structure, predator-specific escape behaviors, and the phenology of larval development.

Do All Portable Cases Constructed by Caddisfly Larvae Function in Defense?

“…We hypothesized that those case materials that have been experimentally documented to resist greater forces (i.e., mineral cases) would provide greater resistance against predation and increase chances of survival, as has been demonstrated previously (Otto and Svensson 1980; Johansson 1991; Nislow and Molles 1993; Wissinger et al 2006). Although the relative strength of the cases used in this study was not measured, these cases qualitatively appeared to reflect this gradient; rock cases were generally stronger than stick cases, which were stronger than leaf cases (BGG personal observation).…”

“…For example, Wissinger et al (2004) demonstrated that individual caddisflies that possessed a case were less likely to succumb to cannibalism compared to their caseless counterparts. Furthermore, although several species of caddisflies that build cases of different material had different survivorship against predatory salamanders, each had higher survival when left in their case relative to individuals of that species that were removed (Wissinger et al 2006). These results, in conjunction with the results presented here, indicate that case construction is an important adaptation for reducing predation.…”

Top‐down control of prey increases with drying disturbance in ponds: a consequence of non‐consumptive interactions?

“…Furthermore, organisms inhabiting physically stressful environments often face life‐history constraints that force individuals to trade‐off resistance to biotic interactions with rapid development or efficient resource use (Power, Parker & Wootton ; Wissinger et al . ; Edwards & Stachowicz ). These trade‐offs may strengthen top‐down control in disturbed habitats.…”

High interspecific variation in nutrient excretion within a guild of closely related caddisfly species

“…As a consequence of trade‐offs between traits that facilitate coexistence with predators and those that facilitate the completion of larval development before ponds dry, the particular combinations of species vary among pond permanence types (temporary vs. permanent; Wissinger et al. , ). These closely related caddisfly larvae (Ruiter et al.…”