Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary ti...

Behavioral decisions made under the risk of predation: a review and prospectus

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

We examine why demographic models should be used cautiously in Population Viability Analysis (PVA) with endangered species. We review the structure, data requirements, and outputs of analytical, deterministic single-population, stochastic single-population, metapopulation, and spatially explicit models. We believe predictions from quantitative models for endangered species are unreliable due to poor quality of demographic data used in most applications, difficulties in estimating variance in demographic rates, and lack of information on dispersal (distances, ages, mortality, movement patterns). Unreliable estimates also arise because stochastic models are difficult to validate, environmental trends and periodic fluctuations are rarely considered, the form of density dependence is frequently unknown but greatly affects model outcomes, and alternative model structures can result in very different predicted effects of management regimes. We suggest that PVA (1) evaluate relative rather than absolute rates of extinction, (2) emphasize short-time periods for making projections, (3) start with simple models and choose an approach that data can support, (4) use models cautiously to diagnose causes of decline and examine potential routes to recovery, (5) evaluate cumulative ending functions and alternative reference points rather than extinction rates, (6) examine all feasible scenarios, and (7) mix genetic and demographic currencies sparingly. Links between recovery options and PVA models should be established by conducting field tests of model assumptions and field validation of secondary model predictions.

On the Use of Demographic Models of Population Viability in Endangered Species Management

The Northern spotted owl is a small, predatory bird native to the coniferous forests of the Pacific Northwest. Its preferred habitats are the old-growth forest communities of that region. These habitats have been extensively logged during the last century, reducing both the quantity of habitat available to this subspecies of owl and greatly increasing the fragmentation of remaining habitat. Population Viability Analysis (PVA) is intended to be a structured, systematic and comprehensive examination of the interacting factors that place a population at risk of chance extinction, especially as these relate to population size and distribution. The number of species listed as threatened or endangered is expected to grow rapidly in the coming decades, primarily because of loss of habitat. There are many habitat-limited species, such as narrowly endemic plants and some sedentary invertebrates that occur in low numbers or few sites that a PVA is superfluous.

Population Viability Analysis

Allee effects: population growth, critical density, and the chance of extinction

Birds have been assumed to have a constant adult mortality rate in which a constant fraction of a cohort dies in each age interval. Average annual mortality rates reported for many species would result in exceedingly long potential life spans, and it seems more reasonable to assume that avian mortality is age dependent. Data on the mortality and survivorship of several species of birds are analyzed and alternative models of age-dependent mortality are discussed.

https://www.jstor.org/stable/pdfplus/2459849.pdf

Mortality rates and survival of birds

Pickens (e.g., 1930, 1941, 1968) has listed native and introduced plants in the Nearctic region that are regularly visited by birds. The figwort (Scrophulariacae), mint (Labiatae), and pea (Leguminosae) families contain the greatest number of ornithophilous plants, and the predominant flower color among plants visited by birds is red. Hummingbirds are by far the most important group of flower-pollinating birds in the New World and their apparent tendency to visit red flowers has drawn particular attention. In California the only flowers which are specifically adapted to pollination by hummingbirds have flower colors of some shade of red, while non-red flowers that are also visited by hummingbirds are shared with other pollinators, usually insects (Grant 1966). These and similar observations have led to the popular belief (Bent 1940; Amadon 1966) that hummingbirds have an innate preference for red, and that this has led to natural selection for red flowers among ornithophilous plants. After an extensive review of the literature, Grant (1966) concluded that the "experimental evidence does not support the assumption that hummingbirds prefer red to other colors." Unfortunately, most of the statements made about color preference in hummingbirds have been based on field observations where there was no opportunity to manipulate variables that might affect feeding behavior, and there have been few valid experiments designed to answer this question. The available evidence suggests that the position of a food source is more important than its color (Lyerly et al. 1950; Grant 1966; Collias and Collias 1968) and that color preference can be learned if there is a differential reward (Bene 1941; Collias and Collias 1968). Even when trained to a particular color, Anna's Hummingbirds (Calypte anna) frequently showed "exploratory shifts" to other colors, and Collias and Collias (1968) noted that this "increases the probability that flowers of different species will be discovered to be profitable just as soon as they begin to have a good nectar flow."

https://www.jstor.org/stable/pdfplus/1365757.pdf

Feeding Activity and Color Preference of Ruby-Throated Hummingbirds

Life-threatening air rifle injuries to the heart in three boys

Endangered Species: Models and Predictions

The ruby-throated hummingbird has the most extensive breeding distribution of any hummingbird species in North America. In its most northern distribution in Canada, its spring arrival often occurs before herbaceous flowers are in bloom, and in many parts of its range it breeds in habitats where floral nectar is scarce or unavailable. Evidence is presented to support the hypothesis that the dates of spring arrival and northern breeding distribution of the ruby throat, and probably the rufous hummingbird, are determined by a commensal relationship with the yellow-bellied sapsucker, in which the principal energy source for the hummingbirds is sucrose in sap from trees drilled by the sapsuckers.

Richard S. Miller

Papers

Mortality rates and survival of birds

Feeding Activity and Color Preference of Ruby-Throated Hummingbirds

Life-threatening air rifle injuries to the heart in three boys

Endangered Species: Models and Predictions

Hummingbird–sapsucker associations in northern climates