The interplay between resource supply and demand determines the influence of predation on prey body size

Abstract

8Predation has been shown to either increase or decrease the body mass of fish, along with variable 9 changes in growth rate. The mechanisms underlying these contrasting responses are not well 10 understood. Here we compared intraspecific body size and growth responses to predation against a 11 backdrop of 2006 estimates of asymptotic mass and growth constants (i.e., von Bertalanffy parameters) 12 across species. We show that intraspecific responses can be quite large relative to interspecific variation 13 and confirm that the magnitude and direction of body size responses is variable. We then employed the 14 supply-demand (SD) model of body mass evolution to explore how predator-induced changes in 15 resource demand or supply could alter body mass. The SD model predicts that any combination of 16 increasing/decreasing body mass and increasing/decreasing growth rate is possible when predation risk 17 is increased, which is consistent with the literature. Finally, we use three case studies to illustrate how 18 the interplay of resource supply and resource demand determine the actual body mass and growth rate 19 response to predation. 20

Is oxygen limitation in warming waters a valid mechanism to explain decreased body sizes in aquatic ectotherms?

“…Moreover, even if resource density is temperature-independent, increased predation risk at high temperatures (see next section) may cause behavioural shifts in the prey that will inhibit foraging (Lima & Dill, 1990) and thus effectively reduce food supply and change body size (DeLong & Walsh, 2015). This mechanism of food supply and demand is linked to external ecological conditions, and is therefore different to the largely intrinsic oxygen supply/demand hypotheses discussed above.…”

“…Alternatively, changes in the ratio of protein and carbohydrate availability can be affected by different temperatures and subsequently affect adult body size, at least in terrestrial ectotherms (Lee, Jang, Ravzanaadii, & Rho, ). Moreover, even if resource density is temperature‐independent, increased predation risk at high temperatures (see next section) may cause behavioural shifts in the prey that will inhibit foraging (Lima & Dill, ) and thus effectively reduce food supply and change body size (DeLong & Walsh, ). This mechanism of food supply and demand is linked to external ecological conditions, and is therefore different to the largely intrinsic oxygen supply/demand hypotheses discussed above.…”

The ecological consequences of environmentally induced phenotypic changes

“…Here, we manipulate light and bacteria levels to test the hypotheses that (1) Paramecium body size (measured as cell volume) will increase with resource availability (DeLong ; DeLong & Walsh ), (2) larger body size will decrease maximum per capita growth rate (Blueweiss et al . ; Savage et al .…”

“…Ecological interactions and dynamics are also mediated by traits with functional ecological effects, such as, body size (Abrams 2001;Werner & Peacor 2003;Miner et al 2005;Giometto et al 2013;Gibert & Brassil 2014;Gibert & DeLong 2015;Dehling et al 2016). Traits like body size can be determined in turn by resource availability and predation risk: abundant resources often allow organisms to grow large (Anholt & Werner 1998), while predation risk can lead to smaller individuals (Peckarsky et al 2001;Walsh & Reznick 2009), larger individuals (Abrams & Rowe 1996;Werner & Peacor 2003;DeLong & Walsh 2015), or to dynamic changes in body size as predator-prey dynamics unfold . Both resource availability and predation risk are known to be set by environmental conditions (Durant et al 2007;Miller et al 2014;Janssens et al 2015), and traits can respond to environmental changes either plastically (DeLong 2012) or evolutionarily (Grant & Grant 2002).…”

Size‐dependent predation and correlated life history traits alter eco‐evolutionary dynamics and selection for faster individual growth

“…These rapid shifts in traits may cause eco-evolutionary dynamics by changing the underlying ecological interactions Evolutionary demography: the dynamic and broad intersection of ecology and evolution * John P. DeLong jpdelong@unl.edu 1 School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA 1 3 (Hairston et al 2005;Post and Palkovacs 2009;Schoener 2011;. Eco-evolutionary dynamics may play an important role in determining the outcome of selection on life history traits like age and size at maturity because the abundance of interacting species (e.g., predator and prey) may change, altering the strength or direction of selection as well as the availability of resources (Abrams and Rowe 1996;Edeline et al 2007;Walsh and Reznick 2008;DeLong and Walsh 2016). Furthermore, selection itself may reduce heritable trait variation in life history traits, limiting the potential for further responses to selection over time (Wright 1931(Wright , 1949.…”