Community Ecology

Community Ecology

• Community ecology is the study of how all organisms in a region interact with each other– A community is all the organisms living in an area– The community plus the environment is called an

ecosystem

• Two key adjectives for interactions:– Interspecific: between organisms of two different

species– Intraspecific: between organisms of the same species

Types of Interactions

• Interactions can be grouped into many categories– Sometimes the line is blurred between different

types• Predation• Parasitism• Competition• Mutualism• Commensalism

Predation

• Predation is one organism feeding off the flesh of another organism– Herbivores eat plants– Carnivores eat meat– Omnivores can eat both plants

and meat• Interspecific predation is the

typical kind of predation in a species

Intraspecific Predation• Intraspecific predation is

AKA cannibalism• It is not possible to have an

entire species be solely cannibals– Thanks to the laws of

thermodynamics, a species would eat itself out of existence with no fresh input of energy into the population

– Some species of carnivores are opportunistic cannibals

Sample Defenses Against Predation

• Being too big• Being too small• Being too fast• Being able to fly• Camouflage• Have dangerous structures

growing on you• Having a noxious chemical– Mimicking a species with a

noxious chemical

A Note On Warning Coloration

• Many poisonous or venomous species have bright colors (warning coloration) that chordates learn to avoid– Because chordates have

awesome brains!• If one butterfly must be eaten

for the lesson to be learned, it’s too late for that butterfly– So how did it evolve?

Population Genetics

• If a warning coloration appears as a mutation in one family, the remaining family members benefit even though the individual that was eaten still dies

• This causes that gene to be more successful and be passed down– This is the same logic as altruism,

where individuals that die helping their family have their genes passed on indirectly

Parasitism• Organisms that attach to another

organism and feed off its flesh without killing it are parasites (always interspecific)– The line can get fuzzy sometimes

• Many insects target other arthropods with a reproductive strategy called parasitoidism– A parasitoid lays its eggs in a host,

and the eggs hatch and eat the host alive

Competition• Competition is a very prevalent

interaction– Any resource can be competed for

• Plants compete for water and sunlight– Interspecific and intraspecific

• Animals compete for food– Interspecific and intraspecific

• Animals may also compete for mates– Always intraspecific

Results of Competition

• If one species is an inferior at competing, it will suffer competitive exclusion– Will often die out from a given

region• The excluded species may find

more success getting a different resource (occupying a different niche)– This is called resource partitioning– Usually accompanied by

microevolution

Mutualism

• Organisms can cooperate for mutual benefit– Intraspecific mutualism is usually called

social behavior• Sometimes the cooperation is vital to

one or both species’ survival• Sometimes neither species requires it

but it is convenient• There is always some kind of apparent

benefit in interspecific mutualism (or else it doesn’t get selected for!)

Examples of Mutualism• Vital for both: Pollinators and

angiosperms– Pollinators get food, angiosperms

are pollinated• Vital for one: Pink anemone fish

must live in sea anemones (cnidarian) and is immune to its sting– Protects the anemone from other

grazing fish• Not vital: Tickbirds and cleaner

fish eat parasites off larger animals

Commensalism

• An interaction where one side benefits and the other is unaffected– Always interspecific (intraspecific

would fall under social behavior)– The unaffected side is often a tree

• Example: mosses and lichens can grow on trees to get more sunlight and avoid being trampled– Tree is unaffected

Count the interactions!

• https://www.youtube.com/watch?v=LU8DDYz68kM

Microevolution• Microevolution (change in allele

frequencies) can occur due to limiting factors– Something that preferentially kills

large organisms will favor small organisms, etc.

• A good example is guppies in streams that are hunted by other fish– When hunted by larger predators,

smaller guppies result– When hunted by small predators,

larger guppies result

Genetics Over Time

• When small guppies (from streams where they are hunted by large fish) are grown in lab aquariums they are still small– They are expressing more alleles that make them

smaller as adults– Also usually reproductively active sooner

• These microevolutionary changes add up over time– The different pressures can also result in speciation

Advantages of Sizes

• Larger organisms:– Are less vulnerable to smaller predators– May be able to win competition for food and

mates against smaller organisms

• Smaller organisms:– Can be passed over by large predators– Need less food and resources– May become reproductively active sooner

Human Size

• Do you suppose humans have been getting bigger or smaller over the last few hundred years?

• Why?

Adaptive Radiation

• If there is a lot of pressure from competition for resources, the population may undergo speciation to take advantage of new resources– The African seedcrackers show this!

• The sum total of resources a population needs can be thought of as its niche– Species that lose their niche must find a new way

to get their resources quickly or else die out

Genus Panthera• Only a few million years ago,

there was some unnamed species of large cat– Its range covered Africa, Asia and

the Americas• One population became

geographically isolated and became the modern-day Jaguar

• Lions, Tigers and Leopards all still have overlapping ranges (and will very occasionally still interbreed and produce sterile offspring)– So how did that happen?

99 Problems But a Niche Ain’t One• During some of the turmoil of the

ice ages, new niches opened up– WANTED: Large predator that can

use teamwork to bring down large prey; must live in open spaces where pure surprise is difficult

– WANTED: Large predator that hunts without teamwork; must live in jungles where there is more camouflage

– WANTED: Less large predator that can catch and live off smaller prey anywhere

Niche Overlap

• If two species need the same resource, they are in competition for that resource

• The organisms that are in the fiercest competition will probably die off first

• In the case of Lion vs. Leopard, the smallest leopards and largest lions competed with each other the least– Hence, speciation!

See you in lab!

• Wednesday: last day of new material!