Lecture 14: Community Interactions

Covers Chapter 27

Community

• A community’s interacting web of life tends to maintain a balance between resources and the number of individuals consuming them.*

• Interacting populations influence each other and act as a type of natural selection*

• Coevolution: Two interacting species act as agents of natural selection on each other.*

Ecological niche*

• In order to understand community interactions, we must understand the meaning of an ecological niche: an organism’s physical home (habitat)

• Although different species share aspects of their niche with others, no 2 species occupy the exact same niche

• Each species occupies a niche that encompasses all aspects of its way of life:*

– Feeding– Reproduction– Survival– Nesting site– Types of nutrients required to live– Amount of water it needs

Most important community interactions

• Competition

• Predation

• Parasitism

• Mutualism

• (The first 3 are also density-dependent factors that contribute to environmental resistance)

Competition*

• Interactions among individuals who attempt to use the same resource(s)

• Adaptations can reduce the overlap of niches and thus reduce competition– Competitive Exclusion principle: if 2 species attempt to

occupy the same niche, one will outcompete the other

– Resource partitioning: If 2 species occupy very similar niches, each species will actually occupy a smaller niche than if there was only one species

P. aureliaP. caudatum

(a) Grown in separate flasks

(b) Grown in the same flask

Competitive Exclusion

Fig. 27-1

Resource Partitioning

Fig. 27-2

Blackburnianwarbler

Black-throatedgreen warbler

Cape Maywarbler

Bay-breastedwarbler

Yellow-rumpedwarbler

Predation

• Predators kill/eat other organisms

– Herbivores (animals that eat plants)

– Carnivores (animals that eat animals)

• Predators usually always less abundant than prey*

• Predators can survive on different types of prey depending on availability

• Predator-prey interactions can affect evolutionary adaptations*

– If prey become harder to catch, predators evolve to become better predators

– Predators contribute to overall health of prey population by killing the weakest, slowest, perhaps most sick individuals.

Evolutionary adaptations resulting from predator-prey relationships*

• Camoflage: renders animals inconspicuous even in plain sight (Both predators and prey can use camoflage)

• Warning coloration: attracts attention of prey, warns them that prey is bad-tasting or poisonous

• Mimicry: members of one species have evolved to resemble another (non-poisonous prey resembles a poisonous one: predators think they all are poisonous)

• Startle coloration: deters predators by scaring them

• Aggressive mimicry: predator resembles harmless animal to lure prey

• Chemical warfare: toxins for attack or defense

Camouflage by Blending In

Fig. 27-4

Camouflage by Resembling Specific Objects

Fig. 27-5c, d

Camouflage Assists Predators

Fig. 27-6

Warning Coloration

Fig. 27-7

Mimicry

Fig. 27-9c, d

Startle Coloration

Fig. 27-10

Aggressive Mimicry

Fig. 27-6b

Chemical Warfare

Fig. 27-12a

You Tube: Camo & Mimicry

• By Furious Vegetables

Parasitism*

• One organism (parasite) feeds off of another (host)

• Sometimes harms or weakens host, sometimes kill them

• Host can evolve to acquire immunity against parasite• Affects host population by weakening hosts and making

them more susceptible to death from other causes OR by reducing host population (if parasite kills host).

Cordyceps: Attack of the Killer Fungi

• BBC Worldwide

Mutualism

• Interactions between species in which both parties benefit*

• Ex: clownfish/sea anemones (clownfish is protected from prey by hanging out in poisonous sea anemone tentacles, clownfish keep anemones free of parasites and feed on their feces)

Mutualism

Fig. 27-13b

Symbiosis & Anemone Fish:Reel Life of the Andaman

• You Tube: Bubblevision

How do different species affect the community??

Keystone Species

• A species that plays a MAJOR role in determining community structure*

• If keystone species removed, entire community changes*

• Ex: elephants….eat small trees and bushes. This maintains the grassland and prevents forests from becoming overgrown. Grasslands are source of food for many species. If elephants gone, forests would become overgrown and species who live on grasslands would be endangered

How are communities formed?

Succession*

• Communities do not emerge fully formed, they arise through succession: community and non-living environment change structurally over time

• Succession is preceded by a DISTURBANCE: event that disrupts the ecosystem

Succession

• Begins with arrival of a few hardy plants (pioneers)

• Competing plants evolve and displace pioneers• Most communities go through stages to become a

stable and diverse climax community*• Climax community can sustain itself (unless a

disturbance occurs)*

Primary Succession

• Community starts “from scratch”, no trace of a previous community*

• Can take thousands or tens of thousands of years

• Ex: Glacier scours landscape down to bare rock, volcano wipes out all animals and vegetation in a certain area

rock scrapedbare by a glacier

lichens andmoss onbare rock

bluebell,yarrow

blueberry,juniper

jack pine,black spruce,aspen

spruce-firclimax forest:white spruce,balsam fir,paper birch

0

1,000

time (years)

Primary Succession

Fig. 27-16

Secondary Succession

• Occurs after a disturbance changes, BUT DOES NOT WIPE OUT, an existing community*

• Soil, seeds, some animals may remain after the disturbance.

• Ex: Fire

plowedfield

ragweed,crabgrass,Johnsongrass

aster,goldenrod,Queen Anne's lace,broom sedge grass

blackberry,smooth sumac

Virginia pine,eastern redcedar

oak-hickoryclimax forest:white and black oak,bitternut andshagbark hickory

0

100

time (years)

Secondary Succession

Fig. 27-17