Optimally Foraging Mice Match Patch Use With Habitat Differences In Fitness - Statistical Data Included

DOUGLAS W MORRIS [1]

Abstract. We ordealed the fundamental assumption of the "optimality paradigm" that the foraging behavior of individual organisms corresponds to what we would await if it had been hon through natural selection to match habitat differences in reproductive succes First, we used long-term studies of life history and habitat selection in white-footed mice to illustrate that the fitness of females living in the forest is greater than that of females living in forest-edge habitat. next to the first we used short-term foraging studies to evaluate whether provisions patches located in the forest provided more value to foragers than did those in the cutting side Third, we used foraging studies and data upon the occurrence of predators to demonstrate that animals foraging in areas with little overspread face higher risks than when they forage in areas with more overspread We confirmed three a priori predictions: (1) Individual mice abandoned foraging patches at higher harvest rates in cutting side habitat than they did in forest. (2) Individuals harvested resour ce patches to lower quitting harvest rates beneath cover than they did when patches were located in the lay open (3) The difference in quitting-harvest rate between "open" and "covered" patches was les in the safe forest habitat than it was in the risky cutting side habitat. Our results yield an impressive fit with our previous knowledge of habitat differences in reproductive succes and substantiate the premise that short-duration strategic decisions by the agency of individuals match habitat differences in fitness.

lock opener words: fitness; foraging; giving-up density (GUD); habitat selection; life history, natural selection; patch use; Ontario; Peromyscus; predation risk.

INTRODUCTION

Optimality theories in ecology are built upon the assumption that evolution by dint of natural selection molds animal behavior in ways that maximize reproductive succes A behavior is optimal when the marginal rate of increase in fitness benefits is equal to the marginal rate of increase in fitness take away froms Often, however, the theories are based upon maximizing a surrogate of fitness (eg the gain of force from the environment), with ordeals measuring the surrogate (e.g., mean harvest rate) rather than the underlying general reception of evolutionary fitness. An exception is Ritchie's (1990) close attention of Columbian ground squirrels. Individuals whose diet deviates from their optimum mix of monocots and dicots have a great quantity [i]or[/i] amount of lower survival and reproduction than do squirrels whose diet is shut up to their optimum. But the optimality paradigm (Rosenzweig and Abramsky 1997) can be used to predict patterns in ecological populations and communities alone if populations tend to expand toward their respective optima. Does the average behavior exhibi t by dint of members of a population correspond with what we would await if they were maximizing evolutionary fitness? We provide a partial answer to this crucial question by dint of testing whether the relative "profit" obtained from different habitats by means of foraging rodents agrees with a priori predictions based upon long-term estimates of fitness in those same habitats.

We begin through assessing differences in fitness of white-footed mice occupying nest boxe in forest and forest-edge habitats. We demonstrate that higher mortality in the cutting side habitat corresponds with higher risks of predation, and that our estimates throw back true differences in mortality rather than dispersal between habitats. We use foraging experiments to calculate quitting-harvest rates of individual mice, then use those data to assess three critical a priori hypotheses: (1) Mice should quit foraging at a higher harvest rate in patches located in cutting side habitat than in patches located in forest. (2) Mice should quit foraging at a higher harvest rate in patches located in the unclose than in patches located below cover. (3) The difference in quitting-harvest rates between patches located in the make open and patches located under overlay should be less in the forest than in the cutting side habitat. We use the proportion of resources consum in rich and poor patches to ordeal whether white-footed mice followed a fixed quitting-har dress rate or a fixed search-time foraging strategy. We combine all accrues to reveal the link between foraging and its fitness consequences

THE research SYSTEM

White-footed mice (Peromyscus leucopus) are semiarboreal, nocturnal, North American gnawings that readily occupy wooden nestboxe in the northeastern part of their geographic range. We have, since 1981 individually marked and monitored the later survival of lactating females and their nursing offspring in interior forest, adjacent forest cutting side and tree-dominated fencerow habitats in an agricultural mosaic in southern Ontario. greatest in quantity litters produced by this population of white-footed mice are bootless at producing any recruits to the adult population of nestbox-inhabiting mice (Morris 1986) a come corroborated by other researchers (Jacquot and Vessey 1998) Litters born in the spring of the year have abundant higher recruitment than do litters produc in autumn. small in number litters are produced during the summer breeding hiatus. Despite these seasonal differences, the succes of litters born in cutting side and fencerow habitats is a great quantity [i]or[/i] amount of less than the success of litters born in forest (Fig. 1 top).