How Species Interact With Eachother

CommunityGroup of species living close enough

together for potential interaction

Figure 53.1

PredationA Predator eats the PreyPredator adaptations

Locate & subdue preyPrey adaptations

Elude & defend

Competition• Species

competing for the same limited resource.

• Competitive Exclusion Principle • One species

will outcompete the other, driving one to extinction in the ecosystem

ParasitismParasite lives on

or in its host organism

Parasites generally to do not immediately kill their host

SymbiosisMutualism (+/+)

Lichens (algae & fungus)

Ant and Acacia Tree

Commensalism (+/0)Barnacles

attached to a whale

Figure 53.9

Figure 53.5

Cryptic colorationCamouflage

Aposematic colorationBright warning to predators

Batesian mimicryPalatable or harmless species

mimics a harmful model

(a) Hawkmoth larva

(b) Green parrot snake

Figure 53.7a, b

Müllerian mimicryTwo or more unpalatable species

look like each other

(a) Cuckoo bee

(b) Yellow jacketFigure 53.8a, b

What kind of mimicry?Red next to yellow, killA fellow

Red next to black,Friend to Jack

Concept Check!According to the competitive

exclusion principle, what outcome is expected when two species with identical niches compete for a resource? Why?

Species diversityGreater diversity = greater

stability

Community 1A: 25% B: 25% C: 25% D: 25%

Community 2A: 80% B: 5% C: 5% D: 10%

D

C

BA

Figure 53.11

Trophic structureFood chains

Feeding relationships

Limited to 4 or 5 trophic levels

Length of food chain limited by inefficiency of energy transfer

Quaternary consumers

Tertiary consumers

Secondary consumers

Primary consumers

Primary producers

Carnivore

Carnivore

Carnivore

Herbivore

Plant

Carnivore

Carnivore

Carnivore

Zooplankton

PhytoplanktonA terrestrial food chain A marine food chainFigure 53.12

Food websFood chains are

hooked together into food webs

Who eats whom?A species may

weave into a food web at more than 1 trophic level

Humans

Baleen whales

Crab-eater seals

Birds Fishes Squids

Leopardseals

Elephant seals

Smaller toothed whales

Sperm whales

Carnivorous plankton

Euphausids (krill)

Copepods

Phyto-plankton

Figure 53.13

Food Webs

Limits on food chain length

Energetic hypothesisLimited by inefficiency of energy

transfer10%

Dynamic stability hypothesisLong chains less stablePop. fluctuations at lower levels

magnified at higher levels

Community structureRemoving a species

changes the communityDominant species

Most abundant species or highest biomass in community

Keystone speciesExert important regulating

effect on other species in a community

DisturbancesMost communities are in a state of

non-equilibrium due to disturbancesFire, weather, human activities, etc.Not all are negative

(a) Before a controlled burn.A prairie that has not burned forseveral years has a high propor-tion of detritus (dead grass).

(b) During the burn. The detritus serves as fuel for fires.

(c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.

Figure 53.21a–c

Ecological SuccessionThe sequence of community &

ecosystem changes after a disturbance

Transition in species composition over ecological time

(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.

(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.

SuccessionPrimary

Begins in a virtually lifeless area without soil

SecondaryExisting community cleared, but soil

is intact

Succession