Feedbacks between size and density determine rapid eco‐phenotypic dynamics

Abstract

1. Body size is a fundamental trait linked to many ecological processes-from individuals to ecosystems. Although the effects of body size on metabolism are well-known, the potential reciprocal effects of body size and density are less clear. Specifically, (a) whether changes in body size or density more strongly influence the other and (b) whether coupled rapid changes in body size and density are due to plasticity, rapid evolutionary change or a combination of both.2. Here, we address these two issues by experimentally tracking population density and mean body size in the protist Tetrahymena pyriformis as it grows from low density to carrying capacity. We then use Convergent Cross Mapping time series analyses to infer the direction, magnitude and causality of the link between body size and population dynamics. We confirm the results of our analysis by experimentally manipulating body size and density while keeping the other constant. Last, we fit mathematical models to our experimental time series that account for purely plastic change in body size, rapid evolution in size, or a combination of both, to gain insights into the processes that most likely explain the observed dynamics.3. Our results indicate that changes in body size more strongly influence changes in density than the other way around, but also show that there is reciprocity in this effect (i.e., a feedback). We show that a model that only accounts for purely plastic change in size most parsimoniously explains observed, coupled phenotypic and ecological dynamics.4. Together, these results suggest (a) that body size can shift dramatically through plasticity, well within ecological timescales, (b) that rapid changes in body size may have a larger effect on population dynamics than the reverse, but (c) phenotypic and population dynamics influence each other as populations grow.Overall, we show that rapid plastic changes in functional traits like body size may play a fundamental-but currently unrecognized-role in familiar ecological processes such as logistic population growth.

Temperature and nutrients drive eco-phenotypic dynamics in a microbial food web

“…Previous studies showed that predator–prey body size ratios significantly influence temperature and nutrients effects [19,61] and that body size responds to changes in nutrients, temperature and ecological dynamics in specific ways [18]. A recent study showed that the body size of a species can affect its own ecological dynamics [41], which we have also shown here as tight coupling between the phenotypic and ecological dynamics of Euplotes sp . (figure 5).…”

“…To understand the mechanisms through which temperature and nutrients affected the observed food web dynamics, we quantified the reciprocal effects of ecological dynamics and body size on each other using convergent cross mapping (CCM) [52]. The CCM algorithm has now been used multiple times across ecological systems and taxa reliably to estimate the strength of causal effects between variables for which time-series are available [41,[53][54][55][56][57][58] and we followed this specialized literature to infer causation in our data (see electronic supplementary material, appendix II figure S1-S15). Concisely, CCM quantifies the strength of causation of one dynamical variable onto another by measuring the extent to which the time series of one variable can reliably estimate the state of another variable [52].…”

“…Additionally, temperature and nutrients can interactively affect body size: size increases with higher nutrient loads at low temperatures, but decreases at high temperature [18]. Although body size is often considered a response variable, it also has well-known effects on population growth and species interactions [38][39][40][41], so rapid body size responses to temperature, nutrients or both, may have consequences for food web structure and dynamics in warmer climates [42][43][44]. But it is still unclear how rapid, environmentally induced shifts in body size might influence ecological dynamics as they unfold.…”

Climate Change Factors Interactively Shift Peatland Functional Microbial Composition in a Whole-Ecosystem Warming Experiment

“…Changes in protist shape and size have multiple ecological consequences, including population dynamics and ecological interactions within communities (33, 41, 85), as well as total respiration, which decreases with volume (86). Shifts in size and shape can occur quite rapidly and can be as dramatic as 50% or more (61, 87). Likely, species that cannot rapidly respond to temperatures are thus replaced by those that can, leading to high species turnover (Fig.…”

“…This increase in energy availability at the base of the microbial food web should also result in (Fig. 1C): 1) an increase in protist volume in response to more energy availability, 2) an increase in aspect-ratio as increased available energy releases cells from shape metabolic constraints, 3) an increase in sigma-intensity, due to increased production of cellular machinery to process available energy, and, 4) an increase in autotrophy (i.e., decrease in the red/green ratio of cells) relative to heterotrophy (42, 61, 62). We show that warming and CO 2 have significant, negative interactive effects, on the taxonomic and functional composition of peatland protist communities, which has important consequences for C cycling in these systems.…”