Taxonomic Review of Japanese Sponges (Porifera)

Abstract

abstract: Among damselflies in natural lakes, Ischnura species grow faster than coexisting Enallagma species, but Enallagma species have higher survival under predation than Ischnura species. This growth/predation risk trade-off apparently allows these taxa to coexist in ponds and lakes across the Holarctic. However, laboratory studies presented here show that the mechanism assumed by most theoretical and empirical studies to mediate this trade-off, namely activity si-multaneously modulating foraging returns and predation risk, does not operate in this system. Ischnura verticalis larvae were more active than larvae of Enallagma species in a short-term behavioral exper-iment, which explains why Ischnura experiences greater mortality from predation. However, this greater activity did not translate into higher feeding rates. Ischnura verticalis and Enallagma species ate comparable amounts of food in both the short-term behavioral ex-periment and a longer feeding and digestion experiment. In spite of no difference in the amount of food ingested or assimilated, I. ver-ticalis larvae grew faster than Enallagma larvae because they were better able to physiologically convert assimilated food into their own biomass in the presence of mortality threats. From these studies we understand the phenotypic mechanisms determining the antagonistic patterns of relative growth and survival between these two genera, but why these patterns exist remains unclear.