1. Lecture #1 Dynamics of Population growth & Feeding Relationships Unit 8 Community Interactions

2. Limiting Factors (resources) – factors that limit the growth and/or reproduction of an organism or population. Can you think of an example?

3. There are two types of limiting factors 1. Density Independent Limiting Factors- environmental factors that affect population size regardless of the population’s density Many density independent limiting factors are abiotic factors. Examples: long periods of hot or cold weather, natural catastrophes ( forest fires, floods, volcanic eruptions)

4. Density Dependent Factors 2. Density Dependant Limiting Factors – Limiting factors that affect large, dense populations more strongly than small, less crowded ones. Example: Predators, available food

5. Summarizing what you’ve learned Would a drought be a density independent or dependent limiting factor? Explain. Would an infectious disease be a density independent or dependent limiting factor? Explain.

6. How Organisms Interact in Communities In an ecosystem, all members of the web interact with one another. The interactions that we see are the result of a long evolutionary history in which many of the participants of the ecosystem adjust to one another over time.

7. Example – Flowering plants evolved to have an efficient way to disperse their pollen(reproduction) How? They let animals do it for them! Animals that feed on pollen get a meal out of the relationship that they have with the flowering plants

8. Coevolution – The back- and – forth evolutionary adjustments between interacting members of an ecosystem Examples - Wolf & Elk Bees & Flowers Cow & bacteria in their rumen

9. Feeding Relationships There are 3 main types of feeding relationships in nature. 1. Predator- Prey 2. Parasite- Host 3. Plant- Herbivore

10. 1. Predator- Prey Predation - the act of one organism feeding on another. Examples – Lion feeding on a Zebra; Spider feeding on a centipede

11. Predator – any Animal that lives by preying on other animals (usually) from a lower trophic level. Predators have evolved to be stealthy, swift, strong, sharp teeth/ claws, etc

12. Prey - any animal species that is fed upon by another Prey species have evolved ways to escape, avoid, or fight off predators.

13. Predator- prey balance. Predators and their prey have evolved to keep each other’s population in check time populationpopulation

14. As prey increases, predators increase. As predators increase, prey decreases As prey decreases, predators decrease As predators decrease, prey increases

15. Carrying Capacity- the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment

16. 2. Parasite-Host Parasitism (a type of predation) – one organism feeds on and lives in or on another organism, bringing them harm. Parasites are much more abundant and ecologically important than predators in population control All species of plants and animals (even microbes) can be infected with parasites

17. Parasite – an organism that lives in association with another organism (host), from which it obtains organic nutrition. This causes harm to the host. Host – The organism on/ in which a parasite lives. It is the “prey” of a parasite Vector - the organism that carries a parasite from one host to another. Example - Mosquitoes (disease carrying Insects) carry malaria and West Nile virus

18. Parasites don’t usually kill their hosts, but they can in some cases. Why do you suppose they don’t usually kill their hosts?

19. No place like home…….. Answer: Because they depend on the host for a place to live and a food source!

20. 2 Types of Parasites External parasites (Ticks, mosquitoes, fleas, lice, chiggers) They feed on the host’s outer surface.

21. 2 Types of Parasites Internal parasites (tapeworm, ascaris, hookworm, heartworm in canines) The live within the body of their host. For example, the tapeworm attaches in the small intestine, where it takes nutrients from its host. Tapeworm scolex and suckers

22. Parasite- host balance As the population density of a parasite host increases, parasites and their vectors have an easy time finding new hosts. This means that infection rates increase, and die-off results. This helps to control population growth.

23. As the population density of the hosts decrease, transfer of infection is less because there are fewer individuals. This means a decrease in infection and the population is usually able to recover

24. 3. Plant- Herbivore How the relationship works: Herbivores eat plants. If the amount of available vegetation decreases, the population of the herbivore decreases. If the population of herbivore increases, the relative amount of vegetation decreases. Plant-Herbivore balance may only exist if a predator or a parasite is limiting the population of The herbivore. If not, what happens to the ecosystem?

25. Overgrazing - the practice of grazing too many livestock for too long a period on land that is then unable to recover its vegetation.

26. Can plants defend themselves against from herbivores? Plants protect themselves from herbivores in a Variety of ways. Examples Thorns, spines “Chemical warfare”. (Toxic chemical compounds that discourage herbivores from feeding on them.)

27. How do herbivores overcome the defenses of plants? Some herbivores have evolved the ability to feed on plants that are “protected” by particular defensive chemicals. Example Monarch butterfly caterpillars and milk weed The milkweed's "milk“ or white latex is both acidic and somewhat poisonous to many animals.

28. A female monarch lays its eggs on a sprouted milkweed plant Once the eggs hatch, the monarch caterpillar feeds solely on milkweed, and stores the toxin in its body for life. Because of this, predators avoid monarch’s because of their awful taste!

29. Take 2 minutes to summarize how the interactions of community members may help to keep populations in check.