Body size in freshwater planktonic crustaceans: an overview of extrinsic determinants and modifying influences of biotic interactions

Abstract

In view of its fundamental and pervasive influences and impacts on organism physiology and ecology, body size is recognized as a key component of evolutionary fitness and serves as the cornerstone of a seminal contribution in freshwater zooplankton ecology-the Size Efficiency Hypothesis (SEH) of Brooks & Dodson (Science 150:28-35, 1965). While the roles and implications of body size in predation and competition-central tenets of the SEH-have been widely considered and reviewed, no broader integrated synthesis exists of the collective array of body size determinants and their implications in the ecology in crustacean zooplankton-a numerically and functionally dominant group of aquatic organisms. Focusing on planktonic Cladocera and Copepoda in inland waters, in particular, we provide a wide-ranging overview of the direct and/or indirect effects of environmental conditions, consumable resources and biotic interactions that independently and/or collectively influence the phenotypic expression of body size (particularly as length), both within and between species. Some indirect ultimate evolutionary consequences of body size are considered, and we identify some controversies and unresolved issues related to this biologically crucial trait. While by no means exhaustive, our overview reveals a complex nexus of extrinsic proximate abiotic and biotic factors and interactions that influence body size, the phenotypic expression of which in natural systems commonly reflects contrasting outcomes related to conflicting direct and/or indirect selective pressures. In general, however, body size (both interand intra specifically) declines with rising temperature and increases with rising food supply (depending on its quality), although both temperature and food supply exert contrary influences on particular taxa (or life history stages) under certain environmental circumstances. Predation undoubtedly has an overriding influence on body size selection. Depending on its mechanistic basis (visual, tactile or both in tandem), it selectively favours either small or large body size, both within (adults vs. juveniles) and between prey species, which are accordingly often 'size-trapped' between contrasting selective pressures, with consequent indirect effects. The bioenergetics of fundamental physiological processes undoubtedly set constraints on body size and serve as the primary determinant. However, within such

Local forcings affect lake zooplankton vulnerability and response to climate warming

“…body size were strongly inversely correlated with fisheries catches in the main zooplanktivorous species (Spearman's rank correlation test between Daphnia sp. claws size and catches; Lake Geneva, q ¼ À0.511, P ¼ 1.58 3 10 À6 ; Lake Bourget, q ¼ À0.340, P ¼ 0.009; Lake Annecy, q ¼ À0.426, P ¼ 0.008; Appendix D), confirming that even though other environmental conditions such as food quality/quantity or temperature (Hart and Bychek 2011) and invertebrate predation (Branstrator 2005), can affect Daphnia sp. body size, they may not be strong enough to compromise the relevancy of using Daphnia sp.…”

A long-term study on crustacean plankton of a shallow tropical lake: the role of invertebrate predation

“…Thus, the larger species would be visually preyed on and the small-and medium-sized ones would be preyed on by invertebrates, which are oriented by tactile stimuli. However, it is not always easy to distinguish clear patterns and zooplankton communities are generally composed of medium-sized species (Hart and Bychek, 2011). Furthermore, visual predation is not always determinant in controlling zooplankton, since tactile predation can play the main role (Blumenshine and Hambright, 2003).…”

“…In contrast, Iglesias et al (2011) suggested that predation by fish is the major factor explaining the smaller size of zooplankton in warm lakes. Hart and Bychek (2011), in their extensive review of the many factors that could potentially influence zooplankton size, addressed extrinsic factors such as temperature, food and predation, amongst others, besides intrinsic ones. The authors concluded, however, that although a general pattern may occur, different results can arise from distinct ecosystems.…”

The Importance of Phytoplankton Biomolecule Availability for Secondary Production

“…The availability and quality of the biomolecules affects the somatic growth of zooplankton, which is important since the zooplankton body size is directly reflected to its fitness and reproductive output, e.g., the timing of maturity, fecundity, and the survival potential of the offspring (Hart and Bychek, 2011). This is ecologically important because zooplankton have a key position in aquatic food webs by linking the flow of dietary energy and the essential biomolecules from lower (phytoplankton) to upper (fish) trophic levels (Taipale et al, 2016b).…”