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