Population Equilibrium A dynamic balance between births and

Population Equilibrium A dynamic balance between births and deaths. Births = Deaths

Biotic Potential and Environmental Resistance

Population Growth Curves n Reproductive strategies: q Many offspring with low parental care n n q Example fish J-shaped growth curve Few offspring with high parental care n n Example mammals S-shaped growth curve

Population Growth Curves

Density Dependence and Critical Numbers n Factors of environmental resistance are either: q q n 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 n n Predator–prey dynamics Competition q q n Interspecific Intraspecific Introduced species

Predator–Prey Balance: Wolves and Moose

Predator–Prey Balance n n n 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 n n A single species that maintains biotic structure of the ecosystem Example: q q Pisaster ochraceus: a starfish that feeds on mussels (Mytilus californianus) , keeping them from blanketing the rocks Pacific coast intertidal zone

Competition: Intraspecific n Territoriality: defense of a resource against individuals of the same species q q Examples of wolves and songbirds Results in priority access and use of resources

Competition: Interspecific n n Grasslands contain plants with both fibrous roots and taproots Coexist by accessing resources from different soil levels

Introduced Species n Examples (Long Island): q q q q q 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 n n n Introduced to New Jersey in 1988 Spread up to Maine Native Species are diminishing European Green Crab Asian Shore Crab

n Change through natural selection Mechanisms of Species Adaptation q Selective pressure determines which organisms survive and reproduce and which are eliminated.

The Limits of Change n n n Adapt Move (migrate) Die (extinction)

Vulnerability of different organisms to environmental changes

Prerequisites for Speciation n Original population must separate into smaller populations that do not interbreed with one another. n Separated populations must be exposed to different selective pressures.

Speciation: Foxes

Speciation: Galápagos Finches