Transcript COMMUNITY ECOLOGY APES Chapter 8 8-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY Ecologist use 3 characteristics to describe a biological community. 1) Physical appearance-

COMMUNITY ECOLOGY
APES Chapter 8
8-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY
Ecologist use 3 characteristics to describe a biological community.
1) Physical appearance- sizes, stratification, and distribution of its
population and species
•
2)
Edge Effect
Species diversity- a combination of numbers of different
species (richness) and abundance of individuals with each
species (species evenness)
–
–
High richness usually means low evenness (few #’s per species)
Factors affecting diversity are latitude in terrestrial communities and
pollution in aquatic communities.
3) Niche structure- the number of ecological niches,
similarities/differences, and interaction of species with each
other.
SPECIES EQUILIBRIUM MODEL
(THEORY OF ISLAND BIOGEOGRAPHY)
• The number of different species on an island (species richness)
is determined by how fast a species arrives, how fast old species
become extinct, island size and distance from mainland.
Important:
– Balance between rate of immigration of species and rate of
extinction of existing species.
– Size of island (smaller has less diversity) and distance from
mainland (closer to mainland, increases species richness)
GENERAL TYPES OF SPECIES :
– Generalist
– Specialist
– Native: species that normally live and thrive in a particular
ecosystem
– Non-native species: species that migrate into an ecosystem or
are deliberately or accidentally introduced into an ecosystem by
humans.
Also known as: Exotic/ Alien
Problems caused by Non-native species:
• the non-natives have no natural enemies so they can thrive in
the new ecosystem and crowd out the native species:
Examples: Melaleuca plants, Burmese pythons, iguanas
INDICATOR SPECIES:
• A species that serve as early warnings that a community
or ecosystem is being damaged or changed.
• Birds are good indicators because:
• Trout and macro-invertebrates are good
indicators of:
• Amphibians indicate:
KEYSTONE SPECIES:
– species that play a pivotal role in the structure, function, and integrity of an
ecosystem because
• Their strong interactions with other species affect the health and survival of
these species
• They process material out of proportion to their numbers and biomass
Keystone species:
– Pollinate
– Scatter seeds
– Modify habitats
– Predation to control prey populations
– Help plants get nutrients
– Recycle animal waste
EXAMPLES OF
KEYSTONE SPECIES
FOUNDATION SPECIES:
A species that
shapes communities
by creating and
enhancing habitat for
other species
Elephant tearing down tree
5 TYPES OF SPECIES
INTERACTIONS
1) Competition: Two or more animals competing for the same
resources.
Two Types:
• Intraspecific: competition between members of the same
species (mates)
• Interspecific: competition between members of two different
species (food, space, sunlight)
• The more a species niche overlaps, then the more
competition. This can lead to one species migrating, adapting
new behaviors or dying out. Over a long time scale, adaptations
lead to RESOURCE PARTITIONING (warblers) or NICHE
SPECIALIZATION (owls/hawks)
WARBLERS AND RESOURCE PARTITIONING
Niche Specialization
SPECIES INTERACTIONS (CONTINUED)
2) Predation: members of one species feed directly on all or
part of a living organism or other species. They do not live on
or in the other species. One species is clearly harmed and
the other clearly benefits.
Benefits:
Predation can be a good thing for the population of prey species
as predators often weed out the sick and dying animals, thereby
reducing competition amongst the prey species and controlling
population growth. Also, enhances the passing of successful
genetic traits to the next generations. (Sharks)
• Predators have characteristics that help them catch
prey, such as:
• Running fast
• Good eyesight
• Hunting in packs
• Camouflage for ambush
Give examples!
• Prey have characteristics that help them escape predators, such
as:
• Run fast
• Good sense of smell and eyesight to alert them to the
presence of predators
• Protective shell
• Spines
• Camouflage
• Chemical warfare like poisonous skin
• Foul smells
• Bad tasting
• Warning coloration
• Mimicking a predator
• Examples:
SPECIES INTERACTIONS (CONTINUED)
3) Symbiosis: a long lasting relationship in which species
live together in an intimate association. (3 major symbiotic
relationship)
Parasitism: when one species feeds on part of another
organism (host) by living on or in the host. In this
relationship the host is harmed and the parasite benefits.
Examples:
Mutualism: symbiotic relationship in which both species
involved benefit from the relationship. Ways in which this
happens are pollination, providing food, and providing
shelter.
Examples:
Commensalism: a symbiotic relationship in which one
species benefits and the other species is neither helped nor
harmed.
Example:
ECOLOGICAL SUCCESSION:
COMMUNITIES IN TRANSITION
Ecological Succession: One characteristic of all
ecosystems is that they change over time due to
changes in environmental conditions.
There are 2 types of succession:
• Primary succession
• Secondary succession
PRIMARY SUCCESSION:
• Succession that starts with an essentially lifeless area where there
is no soil or bottom sediment in an area.
• Examples include new lava, an abandoned parking lot, land exposed
from retreating glaciers, etc.
• Succession happens in stages:
1) Pioneer species move in and make soil: Ex. Lichens and mosses
2) When enough soil is made and spread out, then plants that are small and close
to the ground move in. These plants can live under harsh conditions and usually
have short lives. They are called early successional species. Examples: small
annuals
3) After hundreds of years, there is enough soil for
Mid-successional species. Examples: small herbs/shrubs
4) As the Mid-successional plants grow they create enough shelter for Late
successional species such as: trees.
SECONDARY SUCCESSION:
• Begins in an area where the natural community of organisms has
been disturbed or destroyed, but the soil remains.
For example:
• abandoned farms, burned or cut forests, and heavily polluted streams.
• Secondary succession occurs in the same way as primary starting with
pioneer species and ending with late successional species.
• Climax community- stable, self-sustaining community at the ending
stages of ecological succession.
Factors that affect the rate of succession and how
one species replaces another:
1) Facilitation – one species makes a area suitable for species
with different niche requirements (Ex. Lichens, mosses gradually
build up soil for small grasses to colonize site)
2) Inhibition – earlier species hinder the growth of later species
(release toxic chemicals to reduce competition)
3) Tolerance – late successional species are unaffected by earlier
successional species
DISTURBANCES CAN AFFECT SUCCESSION:
• Some disturbances can be beneficial in the long run
like fire, because they increase biodiversity, clear out
excess brush, renew nutrients and encourage other
species to grow. Bog succession animation
• Some catastrophic disturbances can convert the
ecosystem back to a lower level of succession. It’s an
ongoing struggle to always progress towards a climax
community.
• Intermediate disturbance hypothesis- communities
that experience fairly frequent disturbances have the
greatest species diversity. (allows time to create openings for
colonizing species but infrequent enough to allow some species
to mature)
ECOLOGICAL STABILITY AND SUSTAINABILITY
• 3 aspects that lead to stability of a living system
1. Inertia/persistence – ability of a living system to resist
being disturbed or altered
2. Constancy- ability of a living system to keep its numbers
within limits of available resources.
3. Resilience- ability of a living system to repair damage
after an external disturbance that is not too drastic.
Complexity- Populations with more biodiversity are
more stable. More biodiversity means greater
primary productivity and more resilience.
EVERYTHING IS CONNECTED!
• There is overwhelming evidence that human
disturbances are disrupting important ecosystem
services that support and sustain all life and
economies. Taking action to prevent these disruptions
even if they haven’t happened yet is the precautionary
principle. (“Better safe then sorry” approach)