An individual‐based model of ectotherm movement integrating metabolic and microclimatic constraints

Abstract

An understanding of the direct links between animals and their environment can offer insights into the drivers and constraints to animal movement. Constraints on movement interact in complex ways with the physiology of the animal (metabolism) and physical environment (food and weather), but can be modelled using physical principles of energy and mass exchange. Here, we describe a general, spatially explicit individual‐based movement model that couples a nutritional energy and mass budget model (dynamic energy budget theory) with a biophysical model of heat exchange. This provides a highly integrated method for constraining an ectothermic animal's movement in response to how food and microclimates vary in space and time. The model uses r to drive a NetLogo individual‐based model together with microclimate and energy‐ and mass‐budget modelling functions from the r package “NicheMapR”. It explicitly incorporates physiological and morphological traits, behavioural thermoregulation, movement strategies and movement costs. From this, the model generates activity budgets of foraging and shade‐seeking, home range behaviour, spatial movement patterns and life history consequences under user‐defined configurations of food and microclimates. To illustrate the model, we run simulations of the Australian sleepy lizard Tiliqua rugosa under different movement strategies (optimising or satisficing) in two contrasting habitats of varying food and shade (sparse and dense). We then compare the results with real, fine‐scale movement data of a wild population throughout the breeding season. Our results show that (1) the extremes of movement behaviour observed in sleepy lizards are consistent with feeding requirements (passive movement) and thermal constraints (active movement), (2) the model realistically captures majority of the distribution of observed home range size, (3) both satisficing and optimising movement strategies appear to exist in the wild population, but home range size more closely approximates an optimising strategy, and (4) satisficing was more energetically efficient than optimising movement, which returned no additional benefit in metabolic fitness outputs. This framework for predicting physical constraints to individual movement can be extended to individual‐level interactions with the same or different species and provides new capabilities for forecasting future responses to novel resource and weather scenarios.

Forecasting species range dynamics with process‐explicit models: matching methods to applications

“…Combining multiple approaches (e.g. using output from an eco‐physiological model as input into an IBM or population model) could draw on the strengths of different approaches (Malishev et al ; Thomas & Bacher ). However, more complex models can take longer to build, lack appropriate data to parameterise, and can also be more difficult to interpret and communicate to other researchers and decision‐makers (Dormann et al ).…”

Field tests of a general ectotherm niche model show how water can limit lizard activity and distribution

“…); (4) our use of a steady‐state heat budget model rather than a transient model (but see Malishev et al. for an application of a transient model to this species); and (5) variations in “personality” and motivational state among individual lizards (Godfrey et al. , Spiegel et al.…”

“…The model was run for two extremes of shade, allowing spatially implicit thermoregulatory behavior (see Malishev et al. for an example of a spatially explicit implementation).…”

A mechanistic model to scale up biophysical processes into geographical size gradients in ectotherms

“…One mechanistic interpretation of size gradients in ectotherms is based on the notion that heat and water balances of differently sized animals differ across macroclimate gradients (Kearney, Shine, & Porter, ; Kearney, Simpson, Raubenheimer, & Kooijman, ; Olalla‐Tárraga et al, ). The heat balance of terrestrial ectotherms is determined by their body size and morphology, which affect the fluxes of both heat and water (Seebacher, Grigg, & Beard, ; Stevenson, ; Tracy, Christian, & Tracy, ), and by their behaviour, which determines the use of different thermal environments in their habitat (Kearney et al, ; Malishev, Bull, & Kearney, ; Sears et al, ; Sunday et al, ). Alternative interpretations of how body size and behavioural thermoregulation influence heat balances of terrestrial ectotherms lead to different and often opposing predictions of body size patterns.…”