Revisiting the Role of Individual Variability in Population Persistence and Stability

Abstract

Populations often exhibit a pronounced degree of individual variability and this can be important when constructing ecological models. In this paper, we revisit the role of inter-individual variability in population persistence and stability under predation pressure. As a case study, we consider interactions between a structured population of zooplankton grazers and their predators. Unlike previous structured population models, which only consider variability of individuals according to the age or body size, we focus on physiological and behavioural structuring. We first experimentally demonstrate a high degree of variation of individual consumption rates in three dominant species of herbivorous copepods (Calanus finmarchicus, Calanus glacialis, Calanus euxinus) and show that this disparity implies a pronounced variation in the consumption capacities of individuals. Then we construct a parsimonious predator-prey model which takes into account the intra-population variability of prey individuals according to behavioural traits: effectively, each organism has a ‘personality’ of its own. Our modelling results show that structuring of prey according to their growth rate and vulnerability to predation can dampen predator-prey cycles and enhance persistence of a species, even if the resource stock for prey is unlimited. The main mechanism of efficient top-down regulation is shown to work by letting the prey population become dominated by less vulnerable individuals when predator densities are high, while the trait distribution recovers when the predator densities are low.

Thermal response of ingestion and egestion rates in the Arctic copepod Calanus glacialis and possible metabolic consequences in a warming ocean

“…Bautista and Harris 1992;Barquero et al 1998), and variability in size within stage CV of C. glacialis can be high (Gabrielsen et al 2012). However, experiments investigating individual ingestion rates of C. glacialis CV feeding on identical T. gravida cell concentrations as used in our experiments indicate individual variation of 42 % independent of body (Morozov et al 2013). Even though we present group data of 6-10 individuals, much of the remaining variation could be ascribed to individual variability.…”

Context‐dependent individual behavioral consistency in Daphnia

“…There are already several invertebrate studies showing consistent behavioral types (Sih and Watters 2005, Reaney and Backwell 2007, Briffa and Greenaway 2011, Schuett et al 2011, although a recent review highlighting the discrepancy between personality research in vertebrates and invertebrates lists only few studies concerning larger aquatic invertebrates, such as mollusks, large crustaceans, and cnidarians (Kralj-Fiser and Schuett 2014). To our knowledge, only one study has focused on consistent behavioral differences in a planktonic organism, showing individual differences in consumptive rates in marine copepods (Morozov et al 2013). This shows that consistent individual differences in behavior in aquatic invertebrates are likely a widespread and critical phenomenon.…”

Towards developing a general framework for modelling vertical migration in zooplankton

“…The existing framework of modelling evolution of infinite-dimensional traits is usually based on the canonical equation of adaptive dynamics [13,53], and approach is a complementary one since it allows us to take into account an arbitrary mutagenesis process as well as the evolution of a complex initial distribution of strategies which are not close each other, which cannot be represented by the canonical equation. Also, this approach allows us to model fast evolution in physiologically structured populations, which has so far been done only for a single trait value [51]. Using equation (4.22) in the generalized parameter space we demonstrate that only high mutation rates can affect the eventual selection process: a weak mutagenesis still results in a strong selection where only a narrow distribution of strategies can survive in the long run (see Fig.7).…”

“…We suggest k(w, v) should be a monotonically decreasing function of the distance ||v − w|| in the genotype space V . In general, the equation describing the evolutionary dynamics of the distribution of strategies (2.3) across the space V is given by [40,51] …”