Chapter 4Chapter 4Ecosystems: Ecosystems:

How They ChangeHow They Change

Population Dynamics:Population Dynamics:Population Growth curves (p83):Population Growth curves (p83):

J-curves, also known as J-curves, also known as exponential growth, exponential growth, could result in repeated could result in repeated J-curves, S-curve J-curves, S-curve equilibrium or total equilibrium or total devastation.devastation.

S-curves, also known as S-curves, also known as logistical growth, logistical growth, represent populations in represent populations in equilibrium.equilibrium.

Population Growth terms (pp84-86):Population Growth terms (pp84-86): Biotic potentialBiotic potential: The maximum reproductive capacity of an : The maximum reproductive capacity of an

organism under optimum environmental conditions.organism under optimum environmental conditions. RecruitmentRecruitment: The success rate of young reaching a breeding : The success rate of young reaching a breeding

ageage Population explosionPopulation explosion: exponential increase of a population: exponential increase of a population Environmental resistanceEnvironmental resistance: factors that inhibit population : factors that inhibit population

growthgrowth Replacement levelReplacement level: The fertility rate that sustains a stable : The fertility rate that sustains a stable

populationpopulation Carrying capacityCarrying capacity: maximum population that an ecosystem : maximum population that an ecosystem

can support without degradationcan support without degradation Dynamic balanceDynamic balance: the addition of births and subtraction of : the addition of births and subtraction of

deaths continue where a population fluctuates around a deaths continue where a population fluctuates around a medianmedian

Population densityPopulation density: # of individuals per unit area: # of individuals per unit area Critical numberCritical number: minimum # below which the survival and : minimum # below which the survival and

recovery of a species is in dangerrecovery of a species is in danger

FactorsFactors that affect population growth that affect population growth

Density DependentDensity Dependent

Food supplyFood supply

CompetitionCompetition

PredationPredation

DiseaseDisease

Resource availabilityResource availability

Density IndependentDensity Independent

FiresFires

TornadoesTornadoes

DraughtDraught

Habitat disturbanceHabitat disturbance

Extreme Extreme temperaturestemperatures

FloodsFloods

Mechanisms of Mechanisms of Population EquilibriumPopulation Equilibrium

1.1. Predation –prey relationshipsPredation –prey relationships Predation on animalsPredation on animals ParasitesParasites Herbivores eating plantsHerbivores eating plants

2.2. CompetitionCompetition Between plant species can be interspecific if niches Between plant species can be interspecific if niches

overlap creating adaptations (Examples: riparian overlap creating adaptations (Examples: riparian forests, different grasses, mutualistic epiphytes, forests, different grasses, mutualistic epiphytes, balanced herbivory of the rainforests)balanced herbivory of the rainforests)

Territoriality is a result of intraspecific competition Territoriality is a result of intraspecific competition (Ex: wolves staking out territory)(Ex: wolves staking out territory)

Mechanisms of Mechanisms of Population equilibrium (cont)Population equilibrium (cont)

3. Introduced Species (p 94 and 95) alter 3. Introduced Species (p 94 and 95) alter habitats, endanger species, deplete habitats, endanger species, deplete resources, spread disease, and alter resources, spread disease, and alter food websfood webs

Evolution as a Force of ChangeEvolution as a Force of Change

Adaptation through natural selectionAdaptation through natural selection Adaptation to the environmentAdaptation to the environment Limits of change: migration, extinction, Limits of change: migration, extinction,

survival adaptationssurvival adaptations Evolution of a species: Darwin’s finchesEvolution of a species: Darwin’s finches

Drifting continentsDrifting continents

Disturbance and SuccessionDisturbance and Succession

Equilibrium Theory is challenged by:Equilibrium Theory is challenged by: Ecological succession occurs until a climax Ecological succession occurs until a climax

ecosystem is reached (if at all)ecosystem is reached (if at all) Primary succession (p 96)Primary succession (p 96) Secondary succession (p 96)Secondary succession (p 96) Aquatic succession (p97)Aquatic succession (p97) Climate changeClimate change

Disturbance and resilienceDisturbance and resilience Some species are eliminated, changing an ecosystemSome species are eliminated, changing an ecosystem Fires, drought, wind, and storms are often necessary to Fires, drought, wind, and storms are often necessary to

achieve a climax ecosystemachieve a climax ecosystem

Primary and Secondary Primary and Secondary SuccessionSuccession

More SuccessionMore Succession

BiodiversityBiodiversity

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

Implications for humansImplications for humans

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

5 Principles of 5 Principles of Ecosystem SustainabilityEcosystem Sustainability

1.1. For sustainability, ecosystems use sunlight For sustainability, ecosystems use sunlight as their source of energy.as their source of energy.

2.2. Ecosystems dispose of wastes and replenish Ecosystems dispose of wastes and replenish nutrients by recycling all elements.nutrients by recycling all elements.

3.3. The size of consumer populations is The size of consumer populations is maintained such that overgrazing and other maintained such that overgrazing and other forms of overuse do not occur.forms of overuse do not occur.

4.4. Ecosystems show resilience when subject to Ecosystems show resilience when subject to disturbance.disturbance.

5.5. Ecosystems depend on biodiversity.Ecosystems depend on biodiversity.