Population Controls and Community Succession How biotic potential and environmental resistance control population dynamics. The mechanisms of population equilibrium. Problems with introduced species How disturbance initiates community succession and leads to enhanced biodiversity. The resilience of ecosystems subject to disturbance.

Population Equilibrium Births Deaths A balance between births and deaths. What if a natural catastrophe suddenly occurred? Biotic Potential Environmental Resistance

Population Growth Curves After the J-crash? J repeat Establish S Local Extinction No natural enemies. Maximum level supported without degradation =

Population Dynamics Biotic potential: reproductive capacity; factors contributing to an increase in population size and/or distribution. –Reproductive rate –Migration or dispersal –Defenses –Coping strategies –Reproductive strategy

Reproductive strategies: Many offspring with low parental care Few offspring with high parental care

Population Growth Control Environmental resistance: combination of biotic and abiotic factors that limit population increase. –Density-independent: effect does not vary with population density adverse weather habitat loss toxic pollutant climate change –Density-dependent: effect varies with population density infectious disease parasites predators competition

Biotic Potential Vs. Environmental Resistance

Population Dynamics Recruitment: portion that survives to reproductive age. Replacement Level = Adult Mortality Dynamic Balance (fluctuate around a level that never exceed the carrying capacity; equilibrium) Critical Number (Below which extinction results.) Threatened versus endangered species

What are the Mechanisms of Population Equilibrium? Natural Enemies Predator-Prey Host-Parasite Predation on Animals Plant-Herbivore Dynamics Competition Between Plants Animal Territoriality Predator-prey Balance: Wolves and Moose of Isle Royale

Absence of natural enemies like predators allows a herbivore population to exceed carrying capacity which results in overgrazing of the habitat. Again, the population succumbs to disease and crashes; it may or may not recover. Herbivore-Plant Dynamics

The Third Principle of Ecosystem Sustainability The size of the consumer population is maintained so that overgrazing or other overuse does not occur. Primary producers maintain substantial standing biomass. Sheep have overgrazed this western landscape. What would happen if coyotes were reintroduced and the shepard stopped paying veterinarian bills?

Competition Between Plants Plants appear to use the same resources. If used in the same way (“niche overlap”) the most competitive will drive the other to extinction (“competitive exclusion”). How do plants coexist to maintain biodiversity? –Microclimates –Specialized adaptations –Mutualism –Balanced herbivory

In a new habitat with ample resources, a plant population experiences exponential growth creating a monoculture. A host-specific pest flourishes and causes plant dieoff. Resources become free for another plant species. A series of these events for different plant species leads to reduced competition and diverse plant community. Balanced Herbivory

Competition Between Animals Interspecific (between different species) –Niche diversity –Habitat partitioning Territoriality: defense of a resource against individuals of the same species. –Intraspecific –Fish, birds, and mammals –Priority use of resources. –The most fit will parent the next generation.

Tipping the Balance: Introduced Species Rabbits in Australia Domestic cats on islands Zebra mussels in the Great Lakes Why have these introductions resulted in a degradation of the ecosystems? (Think in terms of environmental resistance and biotic potential.)

Assignment #4 Population Equilibrium Mechanisms Plant-herbivore dynamics, territoriality, and predator-prey relationships exist in all types of urban, suburban and rural environments. Spend time in the woods on campus, a garden, your backyard, or a local county park (get outdoors) and look for population interactions. Find, observe, and record as many examples of plant- herbivore (pest) dynamics, plant competition, animal territoriality, and predator-prey relationships as you can over two hours. In your journal, each example should be labeled (plant- herbivore dynamics, territoriality, predator-prey relationships, etc.) and described. Also explain how each of these population equilibrium mechanisms influences population dynamics and ecological succession.