Density-Dependent Cannibalism in Dragonfly Nymphs (Odonata: Anisoptera) Overwintering in Temperate Freshwater Ponds

Abstract

Density-dependent mortality by predation and cannibalism has been observed in aquatic insects such as dragonflies in response to shrinking habitat caused by summer drought. Winter conditions might also reduce the amount of livable habitat in temperate ponds and could augment rates of cannibalism. We hypothesized that cannibalism in dragonfly nymphs would increase in winter due to a seasonal decrease in available habitat caused by stratified lower oxygen levels leading to increased nymph density around pond edges. To determine whether cannibalism in nymphs is density-dependent and size-dependent (i.e., with smaller nymphs consumed) we experimentally manipulated nymph density in aquaria. To evaluate whether these patterns are observed in nature during the winter, we conducted field surveys for nymphs in two ponds across the fall and winter seasons. When nymphs were housed at different densities for 24 h, cannibalism was density-dependent, and only smaller nymphs were preyed upon. Our field surveys found that fewer nymphs were caught in the late winter sampling period (mixed-effects model, P < 0.001), and that these were larger than nymphs caught in the fall, although both patterns were restricted to the deeper pond (P < 0.05). Our results were consistent with the process we hypothesized, and the observed reduction in dissolved oxygen at the bottom of the deeper pond. The lack of significant changes to the relative abundance and size of nymphs in the shallower pond reveals that differences in pond characteristics can influence the degree to which winter conditions induce density-dependent cannibalism among dragonfly nymphs.

Cannibalism and competition can increase parasite abundance for parasites with complex life history strategies

“…These two parasites are ideal for comparing the impacts of cannibalism on their respective transmission and abundance because (1) they have the same hosts and similar ecologies but differ in relevant aspects of their life cycle, and (2) odonate nymphs that serve as hosts for both trematode species have high rates of cannibalism in natural systems (Clark et al, 2021; Crumrine, 2010; Hopper et al, 1996; Wissinger, 1989). Tongueworms are trophically transferred to dragonfly nymphs through zooplankton prey while lungworms infect nymphs through free‐swimming larvae.…”

Heavy Metals Accumulation in Dragonflies (Insecta: Odonata) and Their Microhabitats in District Mardan, Khyber Pakhtunkhwa, Pakistan

“…Odonates complete their early developmental stages in aquatic ecosystem where they are the best suppressors and control agents of macro-invertebrates particularly mosquitos' larvae (Corbet 1999;Din et al 2013;Mitra 2002). However, their early developmental stages can be adversely affected by water pollution (Kadoya et al 2008;Clark et al 2021). Freshwater bodies comprised 1% of earth's surface and to monitoring their good health, dragon ies are used as indicator species because these macroinvertebrates help for indicating changes in water resources (quality) and nearby vegetation (Dolný et Dragon ies are eminent environmental indicators for highlighting various features of ecological changes because they are susceptible to habitat and small scale climatic variations (Fulan et al 2008).…”