Chapter 4 Ecosystems: How They Change

Population Dynamics: Population Growth curves (p83):  J-curves, also known as exponential growth, could result in repeated J-curves, S-curve equilibrium or total devastation.  S-curves, also known as logistical growth, represent populations in equilibrium.

Population Growth terms (pp84-86):  Biotic potential: The maximum reproductive capacity of an organism under optimum environmental conditions.  Recruitment: The success rate of young reaching a breeding age  Population explosion: exponential increase of a population  Environmental resistance: factors that inhibit population growth  Replacement level: The fertility rate that sustains a stable population  Carrying capacity: maximum population that an ecosystem can support without degradation  Dynamic balance: the addition of births and subtraction of deaths continue where a population fluctuates around a median  Population density: # of individuals per unit area  Critical number: minimum # below which the survival and recovery of a species is in danger

Factors that affect population growth  Density Dependent Food supply CompetitionPredationDisease Resource availability  Density Independent FiresTornadoesDraught Habitat disturbance Extreme temperatures Floods

Mechanisms of Population Equilibrium 1. Predation –prey relationships  Predation on animals  Parasites  Herbivores eating plants 2. Competition  Between plant species can be interspecific if niches overlap creating adaptations (Examples: riparian forests, different grasses, mutualistic epiphytes, balanced herbivory of the rainforests)  Territoriality is a result of intraspecific competition (Ex: wolves staking out territory)

Mechanisms of Population equilibrium (cont) 3. Introduced Species (p 94 and 95) alter habitats, endanger species, deplete resources, spread disease, and alter food webs Introduced Species endanger speciesIntroduced Species endanger species

Evolution as a Force of Change  Adaptation through natural selection  Adaptation to the environment  Limits of change: migration, extinction, survival adaptations  Evolution of a species: Darwin’s finches  Drifting continents

Disturbance and Succession  Equilibrium Theory is challenged by:  Ecological succession occurs until a climax ecosystem is reached (if at all)  Primary succession (p 96)  Secondary succession (p 96) Secondary succession Secondary succession  Aquatic succession (p97)  Climate change  Disturbance and resilience  Some species are eliminated, changing an ecosystem  Fires, drought, wind, and storms are often necessary to achieve a climax ecosystem

Primary and Secondary Succession

More Succession

Biodiversity  The most stable of ecosystems maintain population equilibrium through diversity.

Implications for humans  Adaptive management has been adopted by federal agencies to assure sustainability of ecosystems  Plan for the long term and unexpected events  Avoid land uses that deplete resources  Minimize introduction of foreign species

5 Principles of Ecosystem Sustainability 1. For sustainability, ecosystems use sunlight as their source of energy. 2. Ecosystems dispose of wastes and replenish nutrients by recycling all elements. 3. The size of consumer populations is maintained such that overgrazing and other forms of overuse do not occur. overgrazing 4. Ecosystems show resilience when subject to disturbance. 5. Ecosystems depend on biodiversity.