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Species Interactions and Community Ecology

Lecture OutlineType of species interactionsFeeding relationships and energy flowKeystone speciesProcess of successionInvasive speciesEcological restorationEarth’s biomes

Competition

A relationship in which multiple organisms seek the same limited resource

Food, water, space, shelter, mates, sunlight, etc…Intraspecific competition is within a species

Population-level phenomenonInterspecific competition is between two or more species and effects the composition of communities

Competitive exclusion, e.g., zebra mussel in Great LakesSpecies coexistence

Resource partitioning: species adapt to competition by evolving to use slightly different resources

Minimizes interference

Resource Partitioning

Exploitative Interactions:Predation

One species (the predator) hunts, kills, and ultimately consumes another (prey)

Zebra mussels eat phytoplankton and zooplanktonDucks, fish, muskrats, crayfish eat mussels

Drives population dynamics Shows paired cycles: ups and downs in one drive ups and downs in the other

Pressures lead to evolutionary adaptationsPredators to become better huntersPrey evolve defenses against being eaten

Cryptic coloration: camouflage to hide from predatorsWarning coloration: bright colors warn that prey is toxicMimicry: fool predators to think it is a toxic, distasteful, or dangerous

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Predator-Prey Systems Prey Evolve Defensive Adaptations

Exploitative Interactions:Parasitism

One organism, the parasite, depends on another, the host, for nourishment or some other benefit while simultaneously doing the host harm

Don’t necessarily kill the host

Can live in or on the host“On” host: sea lamprey sucks blood of fish“In” host: protists that cause malaria, tapeworms in host’s digestive tract, parasitoid wasp larvae and caterpillar

Coevolution and an evolutionary arms raceHost and parasite repeatedly evolve new responses to each other

Exploitative Interactions:Herbivory

Animals feed on tissues of plantsMost common of exploitative interactions

Insects are most widespread herbivorePlants have evolved array of defenses against being eaten

Produce chemicals that are toxic or distastefulThorns, spines, or hairs

Animals may evolved ways to overcome themAnother evolutionary arms race

MutualismBeneficial interactions between two or more species

Each partner provides some resource or service that the other needsOften occurs between organisms that live in close physical contact: symbiosis

Mycorrhizae: some plant roots and fungiCoral polyps and zooxanthallae (algae)GI tracts and microbes

Free-living organisms that encounter each other once in a lifetime

Pollination: vital to agriculture and the food supplyBees, bats, birds

Ecological Community

Community is a group of populations living in the same place at the same timeSpecies interact

Determine composition, structure, and functionCommunity ecologists study

Which species coexistHow species relate to one anotherHow communities change through timeWhy these patterns exist

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Energy Transfer and Trophic Levels

Who eats whomMatter and energy moves through community

Trophic level: rank in the feeding hierarchy of a food chain or web Producers or autotrophs: first level

Green plants, cyanobacteria, algaeConsumers

Primary consumers are second levelAnimals that eat plants; herbivores

Secondary consumers are the third levelPrey on herbivores; carnivores

Tertiary consumers are fourth levelPrey on secondary consumers

Hawks and owls that eat rodents that ate grasshoppersOmnivores: eat both animals and plants

Detritivores and decomposers eat nonliving organic matter and recycle nutrients

Detritivores such as millipedes and soil insects eat waste products or dead bodiesDecomposers: fungi and bacteria breakdown leaf litter and other nonliving matter and enrich soil

Biomass, Numbers, and Energy Decrease at Higher Trophic Levels

Biomass decreases with each trophic levelNot everything in the lower level gets eatenNot everything that is eaten is digestedEnergy is always being used for metabolism and lost as heat

Fewer organisms exist at higher trophic levels# wolves < # deer < # mice < # plants

Efficiency of energy transfer ~10%When we eat animals products we consume far more energy per calorie gained than when eating plant products

If we all ate corn, there would be enough food for 10X as many people

•Keystone species have far-reaching effects on a community

•Often at top of food web

•Wolves, mountain lions, starfish,otters

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Keystone Species and Ecosystem “Engineers”

Other examples of keystone speciesFungi that decompose dead matterInsects that control plant growthPhytoplankton at base of marine food chain

Ecosystem “engineers”Beavers build dams that turn streams into ponds and swampsPrairie dogs dig burrows that aerate soil and serve as homes for other animals

Invasive SpeciesA non-native species that spread and become dominant in a community

Limiting factors that regulate their population are not present

Predators, parasites, competitorsAs proliferate they can interfere with the community’s normal functioning

IntentionalPerch in Lake Victoria; various grasses in American west; goats, pigs, and rats and extinction of island species Some have had benefits (?): European honeybee

AccidentalChestnut blight, Dutch elm diseaseZebra mussels and the Great Lakes

Zebra Mussels Invade the Great Lakes

Native of western Asia and eastern EuropeDiscovered in the Great Lakes in 1988 but by 1994 had spread to 19 US States and 2 Canadian provincesLarvae well-adapted for long distance dispersalAdults attach to boats and ships

Clog water intake pipes and have cost industry 100s of millions of dollars per yearCompete with open water fish and zooplankton for phytoplankton reducing their numbersSuffocate molluscsBenefit bottom feeding invertebrates and fishClear water so sunlight penetration benefits underwater plants and algaeCurrently being out competed by yet another invasive mussel

Humans(economic loss) Phytoplankton Zooplankton

Plankton-eating fish

Clogged intakepipe of powerplant

Zebramussels

Bottom-feedingfish

Bacteriaand benthicinvertebrates

Nativemusselsand clams

Sunlightpenetratingmore deeplyinto water

Aquatic plants

Impacts of zebra mussels on members of a Great Lakes nearshore community

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Open water fish

Littoral zone fish

Communities Respond to Disturbance in Different Ways

Natural disturbances include climate change, hurricanes, floods, avalanches, volcanic eruptionsResistance - the ability of an ecological community to remain stable in the presence of a disturbanceResilience - the ability of an ecological community to change in response to disturbance but later return to its original stateCommunities may be modified permanently and never return to original state

SuccessionSeries of changes in the composition and structure of an ecological community through time following a disturbancePrimary succession

Follows severe disturbances where no vegetation or soil remainsGlaciers retreat, lakes dry up, lava flows

Begins when a bare expanse of rock, sand, or sediment becomes newly exposed to the atmospherePioneer species arrive and colonize new substrate

Spores or seedsLichen mutualistic fungi and algae

Grow and secrete acids that break down rock surfaceSome small plants, insects and worms arriveLarger plants establish and species diversity

Secondary SuccessionSeries of changes that develops over time, beginning when some event

disrupts or dramatically alters an existing communityFire, hurricane, logging, or farming

Primary Aquatic

Succession

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Recovery of Damaged Ecosystems

Compiled results of 240 peer-reviewed studies that examined large ecosystem recovery following cessation of a pertubation

Years 1910 through 20087 different aquatic and terrestrial ecosystem types worldwidePertubations included

Agriculture, deforestation, eutrophication, invasive species, logging, mining, oil spill, overfishing, power plants, trawling, and interactions (multiple disturbances)

Forests took longest to recover, whereas aquatic systems required less recovery time than terrestrial systems

40 to 50 years versus 10 to 20Ecosystems took the longest to recover from agriculture, logging, and multiple stressors67 studies found no recovery

Jones and Schmitz, PLoS, 2009

Ecological Restoration…is the practice of researching the historical conditions of ecological

communities as they existed before humans altered them and restoring themTall grass prairies of Great Plains and Midwest

Converted to agriculture in 19th centuryRestoration of small patches

Weeding out invaders and competitorsIntroducing controlled fire

Florida everglades4700 mi2 system of marshes and seasonally flooded grasslandsDrying out because water that feeds it managed for flood control, irrigation and developmentDecline in fisheries and wading birds (90-95%)30 year, 7.8 billion dollars to undo dams and canals

San Francisco Bay wetlands restorationSan Pablo Bay Watershed Restoration ProgramNapa-Sonoma Marsh Restoration ProjectSouth Bay Salt Pond Restoration ProjectSkaggs Island, San Pablo Bay National Wildlife Refuge

Earth’s Biomes

A large ecological unit defined by its dominant plant type and vegetation structure Determined primarily by a region’s climate, especially temperature and precipitation

Scientists use climate diagrams or climatographs to depict this info

Roughly ten terrestrial biomes

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• Midlatitude forests with broad-leafed deciduous trees• Oaks, beech, maples

• Occur where precipitation is spread relatively evenly throughout the year

• Temperature moderate, seasonally variable

• Europe, eastern China, and eastern N. America

• Grasses dominate; few trees

• More extreme temperature differences between winter and summer

• Precipitation sparse but stable

• Large grazing mammals

• North America, Asia, South America

• Most been converted to agriculture

• Tall coniferous trees• Cedars, spruces,

hemlocks, fir• Cooler and less

species-rich than tropical rainforest but milder and wetter than temperate deciduous forest

• Precipitation very high• Dark moist forest

interior• Pacific Northwest N.

America; Japan

• Highly diverse biotic communities

• Dark, damp interiors; lush vegetation

• Year-round rain and uniformly warm temperatures

• Found in equatorial regions– Central America,

South America, southeast Asia, west Africa, etc…

• Soil poor in organic matter; is aboveground

• Deciduous trees dormant in dry season

• Occurs at tropical and subtropical latitudes where wet and dry seasons each span about 1/2 year

• India, Africa, South America, and northern Australia

• Temperature warm, seasonally stable

• Precipitation highly seasonally variable

• High biodiversity

• Grassland interspersed with acacias and other trees

• Temperature warm• Precipitation highly

seasonally variable• Large grazing

mammals• Africa, South

America, Australia, India, and other dry tropical regions

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• Temperature warm in most areas, but always highly variable between day and night

• Precipitation very low; driest biome on earth

• Vegetation sparse; growth depends on periods of rain

• Organisms adapted to harsh conditions

• Southwestern North America, Australia, Africa

• Nearly dry as desert but located at very high latitudes

• Artic regions:– Northern edges of Russia,

Canada, and Scandinavia• Extremely cold winters with

little daylight and moderately cool summers with lengthy days

• Lichens and low, scrubby vegetation, no trees

• Permafrost• Temperature cold, seasonally

variable• Precipitation very low• Low biodiversity; high

summer productivity

• Also known as taiga• Coniferous forest with

limited number of species of evergreen trees, such as black spruce, interspersed with occasional bogs and lakes

• Temperature cool, seasonally variable

• Precipitation low to moderate

• Low biodiversity; high summer productivity

• Canada, Alaska, Russia, and Scandinavia (Subarctic regions)

• Densely thicketed evergreen shrubs

• “Mediterranean”climate of mild, wet winters and warm, dry summers

• Experience frequent fire• Plants resistant to fire

and even depend on it for germination

• Mediterranean Sea, coasts of California, Chile, and southern Australia

Altitude Creates Patterns Analogous to Latitudes

Sonoran desert

Desert grassland

Oak woodland

Pine woodland

Mountain spruce-fir forest

Alpine tundra

Aquatic Systems Show Biome-like Patterns

OceansStrips along coastlines, continental shelves, open ocean, deep sea, coral reefs, kelp forests

Coastal systems between terrestrial and aquaticSalt marshes, intertidal communities, mangrove forests, estuaries

Freshwater systems like rivers and lakesFactors shaping aquatic systems

Water temperature, salinity, dissolved nutrients, wave action, currents, depth, and type of substrate (e.g., sandy, muddy, or rocky bottom)

Delineated more by their animal than plant life