Personality interacts with habitat quality to govern individual mortality and dispersal patterns

Abstract

Individual phenotypic differences are increasingly recognized as key drivers of ecological processes. However, studies examining the relative importance of these differences in comparison with environmental factors or how individual phenotype interacts across different environmental contexts remain lacking. We performed two field experiments to assess the concurrent roles of personality differences and habitat quality in mediating individual mortality and dispersal. We quantified the predator avoidance response of mud crabs, Panopeus herbstii, collected from low‐ and high‐quality oyster reefs and measured crab loss in a caging experiment. We simultaneously measured the distance crabs traveled as well as the stability of personalities across reef quality in a separate reciprocal transplant experiment. Habitat quality was the primary determinant of crab loss, although the distance crabs traveled was governed by personality which interacted with habitat quality to control the fate of crabs. Here, crabs on low‐quality reefs rapidly emigrated, starting with the boldest individuals, and experienced modest levels of predation regardless of personality. In contrast, both bold and shy crabs would remain on high‐quality reefs for months where bolder individuals experienced higher predation risk. These findings suggest that personalities could produce vastly different population dynamics across habitat quality and govern community responses to habitat degradation.

The boon and bane of boldness: movement syndrome as saviour and sink for population genetic diversity

“…The trade-off hypothesis [12] posits movement syndrome related fitness trade-offs. For example, bold individuals might take more risks, thereby increasing their mortality, but might have higher reproductive success than shy individuals who survive longer [57]. Although in our study bolder individuals incurred no greater mortality risks (mortality rates were movement syndrome invariant to concentrate on movement driven effects), the interaction of movement syndrome with landscape did reveal reproductive fitness costs.…”

Which mechanisms are responsible for population patterns across different quality habitats? A new approach

“…Additionally, this model quantifies the relative importance of these mechanisms in structuring field patterns and identifies the mechanisms that produce the largest pattern changes, which can help end users focus their efforts. These field patterns are: 1) higher proportion of individuals inhabiting high quality habitat (Belgrad and Griffen ), 2) higher proportion of individuals reproducing on high quality habitat (Griffen and Norelli ), 3) higher proportion of deaths on high quality habitat (Belgrad and Griffen ), 4) individual size distribution that is shifted towards larger crabs on high quality reefs and a uniform size distribution on low quality reefs (Belgrad et al , Belgrad and Griffen ) and 5) individual personality distribution shifted towards bolder crabs on high quality reefs (even after accounting for individual size) and an even personality distribution on low quality reefs (Belgrad et al , Belgrad and Griffen ). Although we used mud crabs as a model organism for this simulation, many of these patterns and associated mechanisms are common in a variety of other mid‐trophic level species.…”

“…Mussel characteristics were uniform while crabs were of varying boldness and size. Boldness dictated individual movement (probability of moving per time step = 0–1) and behavior‐dependent predation risk as bolder individuals expose themselves to predators more (Table 1; Belgrad and Griffen ). Size ranged from 0.5 to 2, representing mature individuals 15–30 mm carapace width, and independently dictated individual boldness (boldness = base personality ± 0.598 × (size difference from median), depending on whether individual size is above or below model median size; Belgrad and Griffen ) as well as predation risk since smaller individuals are more susceptible to predators (Table 1).…”

“…Habitat type governed crab movement patterns (described below), base mortality probability (Table 1) and food availability since mussels were distributed on high‐ and low‐quality habitat at densities approximating field conditions (7.7× greater mussel density on high quality reefs than low quality reefs; Griffen and Norelli ). Habitat quality was initially designed as if habitat degradation stemmed from loss of structural complexity, which can lead to lower mortality on low quality habitat due to lower predator encounters (Olsson et al , Belgrad and Griffen ). Each time step corresponded to one hour and simulations were run for 3600 time steps (~5 months).…”

“…habitat‐dependent mortality, size‐dependent mortality, size‐dependent activity/movement; Cushman , Sih et al ). To realistically parameterize these mechanisms and variables, we drew upon laboratory and field experiments of a model intermediate consumer, the mud crab Panopeus herbstii , where we previously quantified habitat‐, size‐ and personality‐dependent mortality (Belgrad and Griffen , ), movement (Toscano et al , Belgrad and Griffen , ) and consumption (Griffen et al , Toscano and Griffen , ), habitat‐dependent reproduction and energy stores (Griffen and Norelli , Belgrad et al ), as well as the relationship between energy stores, behavior and hunger level (Belgrad et al ). We performed model simulations where each trait and mechanism was independently included or excluded, thereby systematically identifying the role each relationship plays in eliciting population patterns.…”