Population Equilibrium Mechanisms in Communities

1. 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.

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

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

4. 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

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

6. 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

7. Biotic Potential Vs. Environmental Resistance

8. 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

9. 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

10. Herbivore-Plant Dynamics • 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.

11. 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?

12. 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

13. 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.

14. 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.

15. 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.)

16. Assignment #4Population 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.