Download COMMUNITY ECOLOGY - Falmouth Schools

Community Ecology
Chapter 53
• Community - group of species living
close enough for interaction.
• Species richness – # of species a
community contains; relative
abundance - # of members of each
species.
• 2 theories on community
development:
• 1Individualistic hypothesis - species
arrive in community by chance
because of abiotic needs.
• 2Interactive hypothesis - species
are in community because of
similar biotic needs and
interactions between species.
Fluctuations are independent of
one another and constantly
changing.
INDIVIDUALISTIC HYPOTHESIS
Fluctuations are dependent upon one another.
INTERACTIVE HYPOTHESIS
Relationships
• Interspecific interactions relationships between species in
community.
• Defined by how they affect other
species.
• 1Interspecific (between species)
competition - resources are limited.
• Organisms own ecological niche
(specific role in environment).
• If two organisms have same niche,
cannot coexist (competitive
exclusion principle)
Both species occupy different
niches because they require the
same biotic needs.
• Resource partitioning allows two
similar species to coexist.
• Done by differentiating species’
niches.
Same genus of lizards, but the different
species occupy different areas in the trees
to allow the resources to be shared.
*
• 2Predation - 1 species hunts, kills,
eats other (the prey).
• AParasitism - 1 species lives off
other species (may/may not kill
host)
• Predators and prey have own
survival adaptations.
• Predators - claws, fangs, etc.
http://janoelofsesafaris.com/images/update11-01/cheetah1.jpg
• Plants – toxic chemical compounds protect against herbivores.
• Prey - defenses (i.e. blending in to
environment)
• Cryptic coloration - prey uses
coloration to deceive predators.
• aAposematic coloring - present as
warning sign to predators.
• Prey - odors and toxins as defense
against predators.
Frog shows toxicity by presenting with
bright colors.
• bMimicry - organism resembles
another species.
• 1Batesian mimicry - harmless
organism mimics harmful one.
• 2Mullerian mimicry – 2+ species
resemble each other (both species
are not tasteful)
Batesian mimicry
Mullerian mimicry
• Parasites - live on host
(ectoparasite) or in host
(endoparasite).
• Parasitoidism - parasite eventually
kills host.
http://www.sierrapotomac.org/W_Needham/Pictures/Wood_Tick_040307.jpg
• 3Mutualism - both species benefit.
• 4Commensalism - 1 species benefits,
other is unharmed but does not
benefit (barnacles that attach to
side of whales)
Acacia tree and ants – the ants feed off the
tree and receive shelter; in return, the ants
protect the tree from any harmful insects
that may kill the tree.
• Coevolution - 1 species evolves, puts
pressure on another species to
evolve.
• 2nd species relies on 1st species;
must adapt to continue to benefit
(selective pressure)
http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/images/rubythroat/ruby-throated_hummingbird_lg.jpg
• Trophic structure - based on
feeding patterns in community.
• Food chain - flow of energy from
producers up to carnivores.
• Trophic level shows where organism
fits in food chain.
• Food web - more accurate way to
look at feeding.
• Feeding relationships shown in
interrelated way.
• Food chains have limits on length (2
hypotheses):
• 1Energetic hypothesis - length of
food chain limited by inefficiency
of energy transfer along chain.
• 2Dynamic stability hypothesis - long
food chains less stable than short
chains.
• Dominant species - most abundant
or highest biomass.
• Biomass - sum weight of all
individuals in population.
• Keystone species - species that
have regulating effect on entire
community.
• If removed, can affect entire
community.
• 2 models at how food chain is
controlled.
• 1Bottom-up model - producers are
the controlling factor of the
population.
• 2Top-bottom model - consumers are
controlling factor of population.
http://www.iarc.uaf.edu/highlights/2005/coupled_marine_ecosystem/food_web.jpg
Disturbances
• Stability - ability of community to
persist through disturbances.
• Fire, weather, or human activities
can alter communities.
Before
disturbance
After
disturbance
Disturbance in marine community
• Some disturbances necessary for
community to thrive.
Fire is necessary for this community to bring
new wildlife.
Succession
• Succession - sequence of
community changes after
disturbance.
• 1Primary succession- no life, soil not
formed yet.
• Mosses and lichens first; cause
development of soil.
• Example - after glacier retreats.
• 2Secondary succession - after
major disturbance.
• Soil left intact.
• Grasses first, then trees and other
organisms.
• Community’s diversity (biodiversity)
controlled by two factors; size and
biogeography.
• Remember: species richness different species living in a
community; relative abundance - #
of those species living in the area.
Community 1 has higher species richness
Community 2 has higher relative abundance
• Species - richer towards equator,
poorer towards the poles. (due to
climate and evolutionary history of
species)
• Greater the geographic area, more
abundant the number of species.