From Insects to Frogs, Egg–Juvenile Recruitment Can Have Persistent Effects on Population Sizes

Abstract

Understanding what regulates population sizes of organisms with complex life cycles is challenging because limits on population sizes can occur at any stage or transition. We extend a conceptual framework to explore whether numbers of successfully laid eggs determine densities of later stages in insects, fish, amphibians, and snails inhabiting marine, freshwater, or terrestrial habitats. Our review suggests novel hypotheses, which propose characteristics of species or environments that create spatial variation in egg densities and predict when such patterns are maintained throughout subsequent life-cycle stages. Existing data, although limited, suggest that persistent, strong associations between egg and subsequent juvenile densities are likely for species where suitable egg-laying habitat is in short supply. Those associations are weakened in some environments and for some species by density-dependent losses of eggs or hatchlings. Such cross-ecosystem comparisons are fundamental to generality in ecology but demand place-based understandings of species’ biology and natural history. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 52 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Body size dictates physiological and behavioural responses to hypoxia and elevated water temperatures in Murray cod (Maccullochella peelii)

“…the Menindee Lakes fish kill of 2018–2019; Moritz et al, 2019 ); yet our data suggest that loss of smaller fish may be a greater likelihood, but could go relatively unnoticed due to their small size. While the loss of the larger breeding fish from a population is undoubtedly significant for population persistence, the loss of large numbers of juveniles can be equally catastrophic ( Downes et al, 2021 ) particularly in slow growing, long-lived species like M. peelii , since their loss may go unrecognized for many years ( Keevil et al, 2018 ). The present study examined the thermal tolerances of fish up to 2.5 kg, but adult M. peelii can grow up to 100 kg.…”

“…Because the seasonal timing of the development of these conditions coincides with post-spawning juvenile recruitment in M. peelii (late spring and summer) ( Rowland, 1983 ), it is highly likely that a significant range of life stages could be exposed to the extreme environmental changes that accompany protracted low flow periods. If larval or juvenile M. peelii have a reduced capacity to withstand or resist these stressors relative to larger individuals, it highlights a serious concern for this species as losses of these smaller size classes may go undetected until they begin to affect the species at a population level ( Downes et al, 2021 ). This study aimed to investigate the influence of body size on the physiological tolerances of M. peelii to high temperatures and hypoxia following acclimation to high water temperatures.…”

The ecological function of insect egg micropyles

“…Other egg traits, such as egg colouration and camouflage (Guerra‐Grenier, 2019) but also chorion sculpturing and architecture, are likely to play a role in influencing the egg immediate microenvironment through photoprotection, air flow, water and gas exchange. Such traits are likely key determinants of survival in this life stage (Downes et al., 2021) and yet they are under‐researched.…”

Population regulation throughout a complex life cycle

“…Then the deck seemed to reshuffle again: sites with comparatively higher numbers of egg masses did not necessarily have a similarly high number of larvae. This result that may seem counterintuitive, but turns out not to be rare (Downes et al, 2021).…”