Fundamental question How do species interact? –Direct and indirect effects

Kinds of interactions Predation+/- Competition-/- Parasitism+/- Mutualism+/+

Zebra mussels Arrived in U.S. 1988: Great Lakes Native to Caspian and Black sea area of eastern Europe urope%20c.jpg urope%20c.jpg

How did zebra mussels get here? Ballast water: is_________ BW full of marine creatures Most don’t survive sea crossing; some do mid-ocean exchange; problems

Why are zebra mussels so successful? Larvae: adapted for long-distance dispersal Few natural predators in North America –Fish and ducks in native range –Native and introduced fish don’t control them

Zebra mussel interactions Predation +/- –ZM natural predators missing (fish, ducks) –ZM are filter feeders, preying on phytoplankton (bad for phytoplankton; also bad for other phytoplankton feeders  COMPETITION) BUT: water with ZM much clearer, so more sunlight reaches bottom: good for large, rooted aquatic plants AND also good for some fish that use these plants for cover

Other aspects of predation Carnivore: eat other animals Herbivore: eat plants Evolutionary arms race –As predators evolve better ways to catch prey, their prey evolve better defenses –eg: milkweeds and insects that feed on them Milkweed contains compounds poisonous to most insects A few insects tolerate milkweed poisons. As a result, they avoid competition from other insects and gain a defense.

Parasitism Also +/- Parasite weakens host, rarely kills it. WHY? –Endoparasites – internal. eg: tapeworm –Ectoparasites – external. eg: tick

Competition Competition -/- intraspecific (Same Species) or interspecific (Different Species) What do individuals compete for?  RESOURCES Eg: food, mates, nesting spots, roosting spots, shelter from predator, sunlight

Intraspecific competition Imagine: –Plants growing in a field –If low density: low seed production. WHY? –If medium density: increasing seed production. –But, high density: at some density, seed production crashes. WHY? –  sketch how this would look on a graph

Zebra mussel interactions Interspecific competition 1000 ZM can settle on a native bivalve, smother it –ZM compete with other phytoplankton eaters –One ZM can filter a liter or more of water a day

Mutualism Sharing benefits: +/+ Examples? Picture: ants tending aphids. aphids protected from predators, ants get honeydew

Commensalism Taking without harming +/0 Common in tropical forests: epiphytes –Small plants, live on or attached to trees –Mosses, ferns, orchids

Overall impact of species interactions Can be hard to estimate eg: Flowering shrubs live in pine forest. –Both compete for resources such as soil moisture, minerals –BUT the flowers produce nectar that is eaten by insects that prey on other, needle-eating insects. SO, if removed flowering shrub, would impact on pine be positive or negative??

Food web

NICHE = ``ecological niche’’ Loosely: organism’s role in ecosystem Includes where it lives, what it eats, what eats it, what organisms it interacts with, even interactions with abiotic components. NOT synonym for ``habitat’’

Differences in niche Specialists: organisms with a relatively narrow niche. Specific requirements to thrive. Generalists: organisms with broad tolerances EXAMPLES??

Fundamental vs. Realized niche A species may be capable of using wider range of resources than it actually does: fundamental niche Actual role and lifestyle of organism is its realized niche Q: what leads to smaller realized niche?

Limiting resources Any resource that is scarce Can restrict ecological niche Examples: –Mineral content of soil may limit plants –Nest sites may limit breeding population of birds

Resource partitioning When 2 or more species overlap in fundamental niche, they often divide up the resources. Better competitor may force other species to occupy only part of niche = COMPETITIVE EXCLUSION

Resource partitioning

Fundamental vs realized niche Brown anole & green anole in FL. BA is introduced Initially, large niche overlap BA outcompetes GA, restricts its niche Competition is KEY

Ecological levels Individual organism Population Species: fundamental unit of biology. A group of interbreeding (or potentially interbreeding) organisms Community Ecosystem Biosphere

Community ecology How do species interact and coexist? How do communities change through time? What determines the makeup of a community (species identity and number)? Community = all populations that live in the same place at the same time Population = all members of one species in one place at one time

Feeding relationships Producers = green plants = autotrophs Consumers = heterotrophs –Primary 1° –Secondary 2° –Tertiary 3°

Trophic levels and energy relationships

Key understandings What is the source of energy in ecosystems? How is energy transferred between trophic levels? –Rule of thumb: –How is energy lost? Pyramid of biomass Pyramid of numbers

Keystone Species Removing the sea star (the top predator) greatly reduced species diversity. Similar removal of other species had little effect on community structure. (sea star)

Resource Partitioning Closely related warbler species can occupy the same tree if they partition resources.