Population Equilibrium

Births = Deaths

A dynamic balance between births and deaths.

Population Growth Curves

Reproductive strategies: Many offspring with low parental care

Example fish J-shaped growth curve

Few offspring with high parental care Example mammals S-shaped growth curve

Population Growth Curves

Population Dynamics

Environmental resistance: combination of biotic and abiotic factors that may limit population increase Predators, competitors, disease Adverse weather, limited food/nutrients

Biotic Potential and Environmental Resistance

Density Dependence and Critical Numbers

Factors of environmental resistance are either: density-independent: effect does not vary with

population density; e.g., adverse weather density-dependent: effect varies with

population density; e.g., infectious disease Critical number: the lowest population

level for survival and recovery

Mechanisms of Population Equilibrium

Predator–prey dynamics Competition

Interspecific Intraspecific

Introduced species

Predator–Prey Balance: Wolves and Moose

Predator–Prey Balance

Absence of natural enemies allows a herbivore population to exceed carrying capacity, which results in overgrazing of the habitat.

The herbivore population subsequently crashes.

The size of the herbivore population is maintained so that overgrazing or other overuse does not occur.

Keystone Species

A single species that maintains biotic structure of the ecosystem

Example: Pisaster ochraceus: a starfish

that feeds on mussels (Mytilus californianus) , keeping them from blanketing the rocks

Pacific coast intertidal zone

Competition: Intraspecific

Territoriality: defense of a resource against individuals of the same species Results in priority access and use of resources

How do wolves and songbirds establish territory?

Competition: Interspecific

Grasslands contain plants with both fibrous roots and taproots

Coexist by accessing resources from different soil levels

Introduced Species Examples (Long Island):

Mute swans Starling House Sparrows Gypsy Moths Japanese Beetles Pheasants Phragmites Eurasian fresh water clam And LOTS MORE!!!

European Green Crab – Native Species

Asian Shore Crab – Introduced Competitor Introduced to New

Jersey in 1988 Spread up to Maine Native Species are

diminishing

European Green Crab

Asian Shore Crab

Mechanisms of Species Adaptation Change through natural selection

Selective pressure determines which organisms survive and reproduce and which are eliminated.

Adaptations to the Environment

The Limits of Change

Adapt Move (migrate) Die (extinction)

Vulnerability of different organisms to environmental changes

Prerequisites for Speciation

Original population must separate into smaller populations that do not interbreed with one another. List some ways this might happen.

Separated populations must be exposed to different selective pressures. Example: arctic and gray fox

Speciation: Foxes

Speciation: Galápagos Finches

Ecosystem Responses to Disturbance

Ecological succession Disturbance and resilience Evolving ecosystems