16 research outputs found
Recovery and nonrecovery of freshwater food webs from the effects of acidification
Many previous attempts to understand how ecological networks respond to and recover from environmental stressors have been hindered by poorly resolved and unreplicated food web data. Few studies have assessed how the topological structure of large, replicated collections of food webs recovers from perturbations. We analysed food web data taken from 23 UK freshwaters, sampled repeatedly over 24 years, yielding a collection of 442 stream and lake food webs. Our main goal was to determine the effect of acidity on food web structure and to analyse the way food web structure recovered from the effects of acidity over time.
Long-term monotonic reversals of acidification were evident at many of the sites, but the ecological responses were generally far less evident than chemical changes, or absent. Across the acidity gradient, food web linkage density and network efficiency declined with increasing acidity, while node redundancy (i.e. trophic similarity among species within a web) increased. Within individual sites, connectance, linkage density, trophic height, resource vulnerability and network efficiency tended to increase over time as sites recovered from acidification, while consumer generality and node redundancy tended to decrease. There was evidence for a lag in biological recovery, as those sites showing a recovery in both their biology and their chemistry were a nested subset of those which only showed a chemistry trend.
These findings support the notion that food web structure is fundamentally altered by acidity, and that inertia within the food web may be hindering biological recovery. This suggestion of lagged recovery highlights the importance of long-term monitoring when assessing the impacts of anthropogenic stressors on the natural world. This temporal dimension, and recognition that species interactions can shape community dynamics, is missing from most national biomonitoring schemes, which often rely on space-for-time proxies
Modes, mechanisms and evidence of bet hedging in rotifer diapause traits
In this contribution, we review our knowledge on bet-hedging strategies associated with rotifer diapause. First, we describe the ecological scenario under which bet hedging is likely to have evolved in three diapause-related traits in monogonont rotifer populations: (1) the timing of sex (because diapausing eggs are produced via sexual reproduction), (2) the sexual reproduction ratio (i.e. the fraction of sexually reproducing females) and (3) the timing of diapausing egg hatching. Then, we describe how to discriminate among bet-hedging modes and discuss which modes and mechanisms better fit the variability observed in these traits in rotifers. Finally, we evaluate the strength of the empirical evidence for bet hedging in the scarce studies available, and we call for the need of research at different levels of biological complexity to fully understand bet hedging in rotifer diapause