population dynamics A look at the factors that tend to increase or decrease the size of a population.

The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE. Biotic potential = growth rate with unlimited resources. Environmental resistance = all the factors acting jointly to limit population growth.

(environmental resistance) POPULATION SIZE Growth factors (biotic potential) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Abiotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Decrease factors (environmental resistance) Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend Inability to resist diseases and parasites Inability to migrate and live in other Inability to adapt to environmental

Four variables change population size: NATALITY = birth rate MORTALITY = death rate IMMIGRATION = rate of organisms moving in EMIGRATION = rate of organisms moving out

REPRODUCTIVE STRATEGIES Number of individuals Time Carrying capacity K species; experience K selection r species; r selection K

Opportunistic or r-Selected Species cockroach dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

Competitor or K-Selected Species elephant saguaro Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species

Percentage surviving (log scale) SURVIVORSHIP CURVES Percentage surviving (log scale) 100 10 1 Age

Population density affects population growth.

R-strategists populations are most affected by these. DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density. Weather Earthquakes Floods Fires . . . Natural disasters R-strategists populations are most affected by these.

DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density. Predation Disease Availability of food and water Space Negative Feedback!!

INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory. EXTERNAL FACTORS = might include predation and disease.

Competition for resources. Species interactions influence population growth and carrying capacity = SYMBIOSIS Competition for resources. High Low Relative population density 2 4 6 8 10 12 14 16 18 Days Each species grown alone Paramecium aurelia caudatum High Low Relative population density 2 4 6 8 10 12 14 16 18 Days Both species grown together Paramecium aurelia caudatum

Resource Portioning

PREDATION PREY POPULATION PREDATOR POPULATION

Avoiding predators Span worm Bombardier beetle Viceroy butterfly mimics monarch butterfly Foul-tasting monarch butterfly Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake Wandering leaf insect Hind wings of io moth resemble eyes of a much larger animal

Parasitism

Oxpeckers and black rhinoceros Clown fish and sea anemone Mutualism Oxpeckers and black rhinoceros Clown fish and sea anemone

Shark and ramora

Cleaning station Cleaner blenny Sabertooth blenny

Commensalism

Herbivory