Overview of Individual Ecology
Ecological systems are under increasing pressure from environmental change, including climate change, habitat loss and fragmentation, and increasing human populations. To understand the consequences of environmental change, to minimize adverse impacts, and to prioritize actions, conservation managers and policy-makers need to know how ecological systems will be affected. Despite this need, predicting the consequences of environmental change for biodiversity has remained a challenge for ecologists.
The research overviewed on this site is designed to directly address this challenge. It views ecological populations as having properties (e.g., size, survival rate, age distribution, space use) that arise from the behaviour and interactions (e.g., decision rules, behaviour, physiology) of their constituent individuals. The main study species have been coastal and wetland birds (waders and wildfowl), but the approach can be applied to a much wider range of species.
This site explains how the research has been used to predict the effect of environmental change on coastal birds and to provide evidence for environmental management and policy. Coasts and wetlands support vast numbers of protected waders and wildfowl but are also of great importance to humans. Human activities that cause habitat or food loss, disturbance, pollution or changes in water level can reduce the number of birds that can be supported. However, quantifying these eﬀects has previously been difficult, fueling environmental conflicts. The research can address these conflicts by providing the evidence-base for environmental decision-making.
There are three main elements to this research and its application;
Underpinning research improves understanding of the factors that determine the survival, body condition and reproduction of individual animals. These include feeding behaviour, decision-making, interactions with competitors, and energetics.
Predicting feeding rates
Research on the behaviour of waders and wildfowl makes it possible to predict the rates at which they can feed in diﬀerent environments, and how this is influenced by the abundance and size of prey and the density of competitors. In waders, for example, the rate of consuming food in the absence of competition depends primarily on the body mass of the bird species and the mass of the prey being consumed. The amount of competition depends on the time taken to consume prey and the ability of the prey to avoid predation (e.g. by escaping down a burrow, or retreating deeper into the sediment).
Understanding decision rules
Research aims to understand the ways in which animals decide where to feed and what to feed on. Animals often need to make trade-offs in these decisions; for example, deciding where to feed when a location has both a high abundance of food, but also a high risk of being attacked by a predator. The models used on this site often assume that animals feed in the location at which energy can be consumed from prey at the highest rate, but an alternative that can be used is that animals move to locations with the lowest risk of predation. Understanding the rules used by different animals is an important part of the underpinning research.
Measuring the food supply
Measuring the amount of food available is a key part of the research. In intertidal habitats this is done using sediment cores to record the density of invertebrate prey (e.g. worms, molluscs, crustaceans). Size, as well as the abundance of prey needs to be measured, as different bird species consume different sizes of prey, and larger prey, with the size-range consumed, are usually the most profitable. The availability of prey in intertidal habitats depends on its exposure through the tidal cycle, and so the shore height of feeding locations needs to be known, as well as the way in which water level changes through time.
Linking individuals to ecology
Models are used to integrate research on individual animals to predict the consequences of environmental change for whole populations. These models represent the behaviour and physiology of individual animals, and predict the population-level consequences of change from the behaviour and fates of individuals.
Populations can be viewed as collections of individuals, each of which is behaving in ways that maximise its chances of survival and reproduction. For example, individuals will feed in the places or on the types of food that allow them to gain mass or obtain energy at the fastest rate. The overall population size or the proportion of individuals which survive or reproduce then depends on the behaviour and fates of the individuals that comprise the population. This way of viewing changes in ecological populations as emerging from the behaviour of individuals is termed Individual-based Ecology.
Populations are usually comprised of many individuals as so computer models are needed to keep track of how each individual behaves, interacts with others, and to record its ultimate fate. Such models that predict population ecology from the behaviour and physiology of individuals are called Individual-based Models. Developing new models for each new site can be time consuming and so software, called MORPH, has been developed that enables models to be developed more quickly. MORPH has been applied to a wide range of bird species including waders and wildfowl, freshwater fish, and numerous environmental issues.
Testing the accuracy of models
If models are to usefully inform environmental decision-making it is vital that the predictions they make are reliable. Therefore, each model is tested as thoroughly as possible by comparing its predictions to observations in the real system. A wide range of predictions can be tested, but these include the overwinter survival rate of the birds, the proportion of the time birds need to spend feeding to meet their energy demands, the body mass of the birds, the distribution of birds throughout a site, and the range of prey species consumed by the birds.
Supporting environmental decision-making
Models have been used to predict the effect on animal populations of many types of environmental change, including in-combination effects of more than one type of change. Models can be used to test the relative impact of different management or site-development options, to determine which has the minimum effect on wildlife.
Simulating environmental change
It is straightforward for individual-based models to predict the effects of environmental change. One or more model values are changed (e.g. area of habitat, height of sea level, amount of disturbance from people), and the model is then run to simulate a period of time (e.g. an overwinter period). The model animals in the simulation can react to the environmental change in a number of ways, for example moving to an alternative location if habitat is lost, avoiding areas that are highly disturbed by people, or feeding for longer. They respond in ways that maximise their chances of survival and / or reproduction, no matter how the model environment is changed. Their response may allow them to compensate for the environmental change, or the change may lead to more animals dying.
Links to policy and management
The models can be used to support environmental policy and management in several ways. If a set of alternative developments, or management options, are proposed on a site, simulations can be run for each of these to determine which has the greatest or least effect on wildlife, in order to rank alternatives. If a change to a site is expected either in the near or more distant future, simulations can be run to determine whether this change is likely to adversely affect wildlife, allowing policy or management to be put in place accordingly. In-combination effects are often important (e.g. habitat loss combined with increased disturbance), and can be simply simulated by making two or more changes to models simultaneously.
Individual-based models are a valuable means of predicting how changes affects wildlife, but they are relatively complicated and require a user to have some experience of modelling. Ideally, a simpler means of making predictions would allow a wider range of people to predict for themselves the possible impact of environmental change in a site. Although complicated, individual-based models can be used to produce quite simple predictions; for example, thresholds of environmental change beyond which there is a negative impact on wildlife. This approach has been used to provide some simpler means of understanding how change affects coastal birds.