Ecology

• Population: Individuals of one species simultaneously occupying the same general area, utilising the same resources, influenced by similar environmental factors
• Population ecology: The study of changes in population size and composition and of the factors that cause these changes
• Density: The number of individuals per unit area or volume
• Dispersion: The pattern of spacing among individuals
• Methods of measuring density include counting the whole population, counting signs left by organisms, counting numbers present in a set number of plots, and mark & recapture
• Clumped dispersion is when variance / mean > 1 i.e. large variance
• Uniform dispersion is when variance / mean < 1 i.e. small variance
• Random variation is when variance / mean = 1
• Dispersion patterns tend to be highly dependent on the spatial scale of the observer
• Population growth models can be exponential or logistic
• Carrying capacity is the maximum population size that a particular environment can support. It is determined by factors such as food/nutrient abundance, shelter, nesting/roosting sites etc.
• Density-dependent growth regulation is associated with carrying capacity, usually through decreased fecundity or survivorship
• Density-independent growth regulation is usually associated with abiotic factors
• Fecundity is the ability to produce an abundance of offspring
• In crowded populations, increasing population density intensifies competition for resources and results in a lower reproduction rate
• Mechanisms of density-dependent regulation: competition, territoriality, predation, toxic waste, intrinsic physiology, disease
• Predators may capture more food as population density of the prey increases
• High density can cause aggressive interactions and hormonal changes that delay sexual maturation and depress the immune system
• Density-independent regulation is often stochastic meaning it cannot be predicted precisely
• Mutualism is a relationship in which both species benefit
• Parasitism is a relationship in which 1 species benefits at the expense of the other
• Commensalism is a relationship in which one species obtains food or other benefits from the other without harming or benefiting the latter
• Gause's Principle of Competitive Exclusion states that two species or populations cannot inhabit the same niche: one will consistently out-compete the other
• Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species
• A type I survivorship curve is exhibited by humans
• A type II survivorship curve is exhibited by rodents, certain lizards, arthropods etc.
• A type III survivorship curve is exhibited by fishes, birds, seeds, etc.