p27 #1-4 p29#1-4 p35 #1-6, 9-15 Check understanding Previous Questions

ALL ABOUT POPULATIONS

Learning Goals  By the end of this lesson I should be able to…  describe the factors that affect the population size of a species.  Explain the difference between open and closed ecosystems.  Describe three types of interactions in a biotic community

Factors that Affect Population Size  Natality or Births per year  Mortality or Deaths per year  Immigration: Number of individuals moving into a population.  Emigration: Number of individuals moving out of a population.

Open vs. Closed Populations  Open Populations: Affected by all 4 factors.  Closed Populations: Only affected by Births and Deaths.

Factors that contribute to limiting the size of a population. Limits on Populations

Biotic Potential  Maximum number of offspring that a species could produce if there were NO limiting factors.

4 Limiting Factors that affect Biotic Potential  Birth Potential: Maximum number of offspring per birth.  Capacity for Survival: Number of offspring that reach reproductive age.  Procreation: Number of times a species reproduces each year.  Length of Reproductive Cycle: Age of sexual maturity and the number of years an individual can reproduce.

Remember gestation periods

Limiting Factors - Prethinking Biotic potential is often never reached because not all conditions are ideal. Some factors that would limit biotic potential include: 

Environmental Limiting Factors  Biotic: Food availability, number of predators, diseases and competition for resources.  Abiotic: Sunlight, Temperature, Precipitation.

Carrying Capacity  The MAXIMUM number of individuals of a species that can be supported by an ecosystem (determined by availability of resources)

CAUSES of Changes in Population Size  Density-dependent factors: Affect a population BECAUSE of size.  Eg. Food, competition for mates, water, resources, disease and predation  Density-independent factors: Affect a popualtion REGARDLESS of size.  Eg. Flood, fire, drought, destruction of habitat

Interactions among organisms that help to shape the ecosystem in which they live. THREE MAIN TYPES OF INTERACTIONS Community (Biotic) Interactions Competition, Predation, and Symbiosis

1. Competition  More than one organism tries to use a resource at the same time, in the same place.  Can between same species or different species.  Species often adapt to have different niches.  Increases as population size increases.

2. Predation  When one organism eats another organism to obtain food.  Prey have developed ways to avoid being eaten (physical, camouflage, tasting repulsive, mimicry)  Predators have developed ways to catch prey quicker (speed, eyesight, claws)

2. Predation Continued…  Can affect a population by:  Bottom-up: Starts at the bottom. (Primary consumer eats too many plants…)  Top-down: Starts at the top. (Top carnivore eats too many rabbits)

3. Symbiosis  Relationship in which two species live closely together. Three main categories:  Parasitism: One species benefits at the expense of the other species. Symbiosis- A surprising tale of species cooperation

Parasitism Introduced parasite fungus Note that humans have moved and introduced all kinds of parasites to new locations and often when introduced for the first time the organisms have no defense!

3. Symbiosis  Commensalism: One species benefits while the other is neither helped nor harmed.

3. Symbiosis  Mutualism: Both species benefit.  Eg. Leaf-cutter ants and fungus….

p42 #1-3 and p46 #3,4,6 to check understanding Practice