Goals: study different views of the ecological niche, one of the fundamental concepts of ecology.  Examine some of the resources of animals and how animals use resources.

The Lecture:
 

One of the fundamental concepts in ecology is the ecological niche.  Unfortunately, while ecologists all talk about niches, they don't always mean the same thing.  There are two main views of what a niche is; these are:

• the role of species in environment.  This is a rather vague definition.  It refers to the requirements of a species and how it affects and interacts with the environment.
• the requirements of a species in an environment ? what resources it needs, what abiotic factors it tolerates, what interactions with other species it requires, what it can tolerate.  While we can never study the entire set of requirements (the whole niche), we can examine specific requirements, so this may be easier to study than the "role" of a species.  This view of a niche was formalized by Hutchinson; the "Hutchinsonian niche" is defined as a "multidimensional hypervolume" of all requirements of a species in its environment.  To understand this, imagine plotting the survival and reproduction of a species versus a range of values of each resource it requires, abiotic factor it must tolerate, or species with which it interacts.  Each of these factors would be considered a separate niche axis.  If all could be drawn together, this would describe all the requirements, conditions within which a species can occur.  It is "multidimensional" because it includes many different niche axes, and it is a "hypervolume" because it is like a volume (a three dimensional structure) only with more dimensions.

• the fundamental niche refers to the range of tolerances and resources within which a species could theoretically occur
• the realized niche refers to the range of conditions within which a species actually does occur.  This range of conditions is typically narrower than those described by the fundamental niche because there are many sets of abiotic conditions and resources within which a species could occur but does not because it is kept out of them by biotic factors such as competitors, predators, or parasites.

Finally, let's briefly consider the resources required by animals and how animals use resources.  When we consider resources, we should also consider whether or not the can be limiting -- that is, whether they could be the factor in short supply for some species that would limit the size to which populations can grow.  Here's a list of basic resources:

• food (likely to be limiting)
• water (can be limiting, especially in dry environments)
• places to reproduce -- mate, produce offspring (can be limiting)
• cover, shelter from predators (could be limiting)
• oxygen (in most ecosystems, unlikely to be limiting)

• specialists have very specific forms of some resource that they require.  For example, many species of insect herbivores are specialists on just one kind of food plant.  These resources are essential: there is no other plant or form of food that can subsitute for the one required kind
• generalists can use a variety of different forms of some resource that they require.  For generalists, many resources are substitutable: if one is not present, another one can be used
• different foods have different qualities; depending on what animals are eating, they need to spend different amounts of time on foraging.  For example, herbivores are feeding on leafy plant material; such material is low in protein and hard to break down, so they need to take in a lot of it and are likely to spend a lot of time foraging.  Predators feeding on animal material spend more time stalking and catching prey, not so much time constantly eating; animal material is higher in protein and lower in indigestible material
• physiological differences among species affect how they use resources, and the resources they require.  For example, for endothermic species, species with large body size do not require as much energy per gram of body mass to thermoregulate because of their lower SA/V.  Smaller endotherms have much higher energy requirements per gram of body mass because rapid heat loss resulting from their high SA/V requires them to put large amounts of energy into thermoregulation.