1. Organization of Life & Symbiosis

2. How is Life Organized?
Species- all organisms of the same kind that breed together
Ex: squirrels
Populations- all members of a species living in the same area, interbreeding together
Ex: all squirrels at MHS
Communities- interactions between different populations
Ex: all squirrels, trees, pigeons, students, grass, etc MHS
Ecosystems- interactions between all populations and their surrounding environments
Ex: how animals & plants interact with soil, air, water
Distinctions between ecosystems is not always clear
EX: forest on edge of field may share similar organisms.

3. So many organisms, how can they all coexist?
Everything has a habitat- place where it lives.
Everything has a niche- or role in its habitat. How it gets food, interacts with other populations, or service it provides to community.
Generalists- wide range of food & habitats (raccoons, cockroaches)
Specialists- specific food sources & habitats (pandas); less resilient to changes in environment

4. What is the Law of Competitive Exclusion?
No two species will occupy the same niche and compete for exactly the same resources in the same habitat for very long.
Eventually, one species will outcompete the other and push the weaker species out of the habitat, or cause its extinction.
Could result in two insectivores feeding in same tree, just at different times of the day.

5. More on competition…
Compete for food, chemical nutrients in soil, space, mates, etc.
Intraspecific- competition within a species
Trees provide shade so their own seedlings can’t grow underneath them so no competition for sun
Caterpillars eat leaves while adult butterflies eat nectar. Reduces competition for food sources
Some create a territory to prevent competition
Interspecific- competition between two different species
Ex: when different weeds produce numerous seeds & race to cover most ground
secrete substance that inhibits root growth
different herbivores on savanna compete for grasses

6. Besides competition, how else do species interact?
PREDATOR-PREY
Predator- an organism that feeds directly upon another living organism, may or may not kill prey
Includes herbivores, carnivores, omnivores
Help force evolution of prey species
Leads to coevolution- exert selective pressure on each other- evolve in response to each other

7. How else do species interact?
PARASITE-HOST
Parasites feed directly on another living thing but do not kill it in the process.
Ex: ticks suck blood from dog

8. How else do species interact?
COMMENSALISM
one member benefits, the other is not substantially benefited or harmed.
Ex:
cattle egrets feed on insects stirred up by grazing cattle
Clownfish gets protection from sea anemone which is not helped or harmed by fish.
Bromeliads grow on tree branches to reach sunlight

9. How else do species interact?
MUTUALISM
Both members benefit significantly from the relationship
Ex:
Lichens- combo of fungus (provides water & place for algae to grow) and algae (provides food for both)
Insects & their pollinators
Ants and acacia trees

10. How else do species interact?
KEYSTONE SPECIES
A species or group of species whose impact on a community are much larger than would be expected from mere abundance.
Ex: sea otters & kelp beds; tropical figs & frugivores (fruit eaters)
Keystone species increase niche diversity because without them other species cannot survive- may either move to new habitat or become locally extirpated

11. How do organisms defend themselves against predation & parasitism?
Chemical defense- smell bad or taste bad
Batesian mimicry
Harmless species mimics harmful
Ex: monarch butterfly & viceroy butterfly; moth has eyespots, looks like owl
Mullerian mimicry
Two species that are harmful develop same patterns/colors
Most wasps have yellow/black banding patterns
Camouflage- look like dead leaves or twigs or even bird poop