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2.6.1-.4, 2.1.7 Population Dynamics 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. POPULATION SIZE Growth factors (biotic potential) Abiotic Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) 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) Abiotic Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Biotic Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change Four variables change population size: 1. NATALITY = birth rate 2. MORTALITY = death rate 3. IMMIGRATION = rate of organisms moving in 4. EMIGRATION = rate of organisms moving out REPRODUCTIVE STRATEGIES Carrying capacity K Number of individuals K species; experience K selection r species; experience r selection Time 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 SURVIVORSHIP CURVES Population density affects population growth. DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density. 1. Weather 2. Earthquakes 3. Floods 4. Fires . . . Natural disasters R-strategists populations are most affected by these. DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density. 1. Predation 2. Disease 3. Availability of food and water 4. Space Negative Feedback!! INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory. EXTERNAL FACTORS = might include predation and disease. Species interactions influence population growth and carrying capacity = SYMBIOSIS Competition for resources. High Low 0 Relative population density Relative population density High Paramecium aurelia Paramecium caudatum 2 Low 0 Paramecium aurelia Paramecium caudatum Days 8 10 Days Each species grown alone Both species grown together 4 6 8 10 12 14 16 18 2 4 6 12 14 16 18 Resource Portioning PREDATION PREY POPULATION PREDATOR POPULATION Avoiding predators Span worm Wandering leaf insect Poison dart frog Viceroy butterfly mimics monarch butterfly Bombardier beetle Hind wings of io moth resemble eyes of a much larger animal Foul-tasting monarch butterfly When touched, the snake caterpillar changes shape to look like the head of a snake Parasitism Mutualism Oxpeckers and black rhinoceros Clown fish and sea anemone Shark and ramora Cleaning station Cleaner blenny Sabertooth blenny Commensalism Herbivory