Unit 1.2: Community Interactions and Population Dynamics

1. Unit 1.2: Community Interactions and Population Dynamics

2. Guiding Questions for this unit: What are five types of interactions that occur between organisms within a community? How are mutualism and commensalism similar? How are they different? What four factors contribute to the increase or decrease in a population? How does exponential growth differ from logistic growth? What is the “carrying capacity” and how is it represented on a graph?

3. Vocabulary Symbiosis: “sym-” = with, “bio-” = life; unlike organisms that live together Mimicry: the characteristic of resembling something poisonous or otherwise dangerous Aposematic coloring: bright coloration that warns predators that a particular prey is dangerous. Mutualism: symbiotic relationship in which both organisms benefit Commensalism: symbiotic relationship in which one organism benefits and the other is unaffected Carrying capacity: the largest number of individuals an environment can support. Limiting factor: factor that causes population growth to decrease

4. Community Interactions • Five types of interactions between species: • Predation • Predator : has evolved structures and behaviors to help it find, capture, consume prey • Ex: keen eyesight, camouflage, tooth structure

5. Prey : has evolved structures and behaviors to help it avoid, escape, ward off predators • Ex: camouflage, bad-taste, quills • Aposematic coloring: poisonous species is brightly colored as a warning to predators • Wasp, monarch butterfly, coral snake • Mimicry: harmless species resembles poisonous one • Bumblebee, viceroy butterfly, king snake • Plants: (can be considered prey) • physical defenses: thorns, spikes • chemical defenses: poisons (poison oak)

6. Competition: Two species compete for limited resources within a “habitat”. • A “habitat” is the community where an organism lives: • Many species live in the same habitat (like Grass Valley) • A “niche” is the “role” it plays in its habitat: • A niche includes the foods that organism eats, how it gets this food; where it reproduces; and abiotic factors (such as temperature range); where it thrives. (like Bitney) • Different species occupy different niches within the same habitat

7. Competitive Exclusion Principle: two species cannot occupy the same niche in the same habitat at the same time • Whichever of the two species is more efficient at using resources (water, nutrients, light, food, or space) out-competes the other species, survives • Like two students trying to sit in the same seat at the same time.

8. 3 types of symbiosis • Parasitism: • Parasite benefits , host is harmed • Ectoparasite : “ecto-” = external • ex: ticks, leeches, mosquitoes • Endoparasite : “endo-” = internal • ex: bacteria, tapeworms • Cordyceps fungus • Host is not usually killed, b/c then parasite must find new host • Parasites help to keep host population balanced, prevents overpopulation • Host defenses: • Physical: skin • Chemical: tears, saliva, mucus • pH of tears, saliva can inhibit bacterial growth • Mucus: causes clumping of bacteria to allow body to remove it

9. Mutualism: • Benefits both species • ex: pollination: flowers provide food to animals, animals carry pollen to other flowers • “Let me tell you ‘bout the birds and the bees, and the flowers and the trees…” • Commensalism: • One benefits , other is not affected • Clownfish/anemone: clownfish is protected but anemone gains nothing • Pitcher plant, red crab spider: spider gets food, but pitcher plant does too, so plant is unaffected.

11. II. Properties of Populations • 3 characteristics that describe populations • Geographic distribution: area inhabited by a population • Can be small: apple being broken down by bacteria • Or large: the ocean travelled by migrating whales

12. Density: number of individuals per unit of area or volume • Grass Valley has low population density in terms of people but high population density in terms of pine trees. • Los Angeles has high population density in terms of people but low population density in terms of pine trees.

13. Dispersion: how organisms are spaced • Clumped: clustered groups • Because resources (food, living space) are clumped • Social behaviors like herds/flocks/packs are considered “clumped” • Even: consistent distance between individuals • Planned space like a planted orchard • Also occurs when plants release chemicals into soil that prevent other plants from growing nearby • Random: independent locations • ex: seed dispersal by wind

14. III. Population Growth • Growth rate: change in population size over time, dependent on: • Birthrate: # of births in a period of time (↑ growth rate) • Death rate (mortality rate): # of deaths in a period of time (↓ growth rate) • Immigration: individuals moving into a population. (↑ growth rate) • b/c more resources are available • Emigration: individuals moving out of a population. (↓ growth rate) • b/c resources are scarce Growth rate = birth rate – death rate (assumes no migration)

15. Exponential • Exponential Growth: • Unlimited population growth occurs when: • Resources are unlimited: food, water, space, mates • No predation or disease • Ex: bacteria divide/double their population every 20 minutes in optimal conditions. At this rate, in one week, a single bacteria would divide enough to cover entire planet! • Plots shows a steep slope with no leveling at the top • J-shaped curve

16. Logistic Growth: • Limiting resources causes the growth of a population to slow or stop b/c: • Decrease in birthrate or immigration • Increase in death rate or emigration • Plot shows steep slope followed by a leveling at the topof the graph • S-shaped curve

17. Carrying Capacity: • Maximum number of individuals an environment can support • Environment cannot support any more so growth rate levels off • Flat portion at top of logistic growth curve

18. IV. Limits to Growth • Limiting factor: factor that causes population growth to decrease • limited amounts of food/food sources • pandas only eat bamboo, bamboo forests have been cleared, reducing food availability • limited nesting space • limited numbers of mates • limited amounts of water!

19. Density-dependent factors: depend on population size/density • Competition: if more organisms, then more competition for resources; if fewer organisms, then less competition • Predation: predator-prey relationships keep populations in check • If more prey, can support more predators, but when predator population becomes overpopulated, then will drop b/c not enough prey to support all the predators • Parasitism and Disease: if more organisms, then greater chance of infection by parasites. • ex: ant population and Cordyceps fungus in jungles

20. Density-independent factors: affect all populations in similar ways regardless of population size • Natural disasters: droughts, floods, fires • Seasonal cycles: deciduous trees drop leaves = less food for some populations • Human disturbances: damming rivers, clear-cutting forests

21. Warm-up answers for this unit:

22. Warm-up answers for this unit: