COMMUNITY ECOLOGY. Overview: What Is a Community? – Is an assemblage of populations of various...
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Transcript of COMMUNITY ECOLOGY. Overview: What Is a Community? – Is an assemblage of populations of various...
• Overview: What Is a Community?– Is an assemblage of populations of various species living
close enough for potential interaction• The various animals and plants surrounding this watering hole
– Are all members of a savanna community in southern Africa
Figure 53.1
Species interactionsWhen multiple species seek the same limited resource
• Interspecific competition is between two or more species.
• Intraspecific competition is within a species.
Usually does not involve active fighting, but subtle contests to procure resources.
The Competitive Exclusion Principle• The competitive exclusion principle
– States that two species competing for the same limiting resources cannot coexist in the same place
• However, ecologically similar species can coexist in a community– If there are one or more significant difference in their
niches
When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.
The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realizedniche of Chthamalus much smaller than its fundamental niche.
RESULTS
CONCLUSION
Ocean
Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland.
EXPERIMENT
In nature, Balanus fails to survive high on the rocks because it isunable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata.
Low tide
High tide
Chthamalusfundamental niche
Chthamalusrealized niche
Low tide
High tideChthamalus
Balanusrealized niche
Balanus
Ocean
Figure 53.2
Ecological Niches• The ecological niche
– Is the total of an organism’s use of the biotic and abiotic resources in its environment
• The niche concept allows restatement of the competitive exclusion principle– Two species cannot coexist in a community if their
niches are identical
NicheCoexisting competitors may adjust their resource use, habitat use, or way of life to minimize conflict.
Fundamental niche Realized niche
Interspecific competitionAdjusting resource use, habitat use, or way of life over evolutionary time leads to:
• Resource partitioning = species specialize in different ways of exploiting a resource
• Character displacement = physical characters evolve to become different to better differentiate resource use
A. insolitususually percheson shady branches.
A. distichus perches on fence posts and
other sunny surfaces. A. distichus
A. ricordii
A. insolitus
A. christophei
A. cybotes
A. etheridgei
A. alinigar
Figure 53.3
Resource Partitioning•Resource partitioning is the differentiation of niches
– That enables similar species to coexist in a community
Predator–prey cyclesPopulation dynamics of predator–prey systems sometimes show paired cycles: ups and downs in one, drive ups and downs in the other.
Predation drives adaptations in prey
Cryptic coloration:Camouflage to hide from predators
Warning coloration:Bright colors warn that prey is toxic
Mimicry:Fool predators(here, caterpillar mimics snake)
• In Batesian mimicry– A palatable or harmless species mimics an
unpalatable or harmful model
(a) Hawkmoth larva
(b) Green parrot snake
Figure 53.7a, b
• In Müllerian mimicry– Two or more unpalatable species resemble each
other
(a) Cuckoo bee
(b) Yellow jacketFigure 53.8a, b
Parasitism
One species, the parasite, exploits the other species, the host, gaining benefits and doing harm.
Interspecific Competition
Brown Headed Cowbird lays her eggs in nest of different species of bird (referred to as brood parasitism)
Herbivory
One of the most common types of exploitation is herbivory, which occurs when animals feed on the tissues of plants.
MutualismBoth species benefit one another.
Hummingbird pollinates flower while gaining nectar for itself.
Mutualism• Mutualistic symbiosis, or mutualism an
interspecific interaction that benefits both species
Figure 53.9
Amensalism• Amensalism = one species is harmed; the
other is unaffected
• Ex: Sheep and Cattle trample grass to make a trail, kill the grass
• Ex: bread mold penicillium secretes penicillin, a chemical that kills bacteria.
Interspecific Interactions and Adaptation
• Evidence for coevolution– Which involves reciprocal genetic change by interacting
populations, is scarce.Example: snapdragons that many people plant in their
gardens are designed for a bumblebee of just the right weight to trip the opening mechanism.
Example: Predator – Prey
Energy Passes among trophic levels in communities
• By eating different foods, organisms are at different trophic levels, and play different roles in the community.
• Plants and other photosynthetic organisms are producers.
Consumers• Animals that eat plants are primary consumers,
or herbivores.
• Animals that eat herbivores are secondary consumers.
• Detritivores and decomposers eat nonliving organic matter; they recycle nutrients.
Food chains and webs
• Food chain = simplified linear diagram of who eats whom
• Food web = complex network of who eats whom
We can represent feeding interactions (and thus energy transfer) in a community:
QUESTION: Review
a. Producer, secondary consumer, herbivore
b. Producer, herbivore, secondary consumer
c. Secondary consumer, producer, detritivore
d. Herbivore, carnivore, producer
Which of the following lists of trophic levels is in the correct order?
Answer: B
Keystone species• Species that have especially great impacts on other
community members and on the community’s identity
• If keystone species are removed, communities change greatly.
A “keystone” holds an arch together.
Keystone speciesWhen the keystone sea otter is removed, sea urchins overgraze kelp and destroy the kelp forest community.
What Is Disturbance?
• A disturbance– Is an event that changes a community– Removes organisms from a community– Alters resource availability
• Fire– Is a significant disturbance in most terrestrial
ecosystems– Is often a necessity in some communities
(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
Resistance and resilience
• A community that remains stable despite disturbance is showing resistance to the disturbance.
• A community shows resilience when it changes in response to disturbance but later returns to its original state (without human interference)
Ecological Succession• Ecological succession
– Is the sequence of community and ecosystem changes after a disturbance
i.e. It is a series of regular, predictable, quantifiable changes through which communities go
Succession
• Primary succession: Pioneer species colonize a newly exposed area (lava flows, glacial retreat, dried lake bed).
Life has never existed there, no soil present.
• Secondary succession: The community changes following a disturbance (fire, hurricane, logging). Life once existed there….soil is already present.
Examples of Primary Succession
Newly exposed rock from receding glacier
Newly formed volcanic Island
1. Open pond
2. Plants begin to cover surface; sediment deposited
3. Pond filled by sediment; vegetation grows over site
Primary aquatic succession
Climax Community
• The transitions between stages of succession eventually lead to a climax community.
• The climax community remains in place, with little modification, until some disturbance restarts succession.
Human Disturbance• Humans
– Are the most widespread agents of disturbance
• Human disturbance to communities– Usually reduces species diversity
• Humans also prevent some naturally occurring disturbances– Which can be important to community structure
QUESTION: Review
a. The slopes of a Hawaiian volcano’s new lava flow
b. A South Carolina coastal forest after a hurricane
c. Alaskan land just uncovered as a glacier melts
d. A new island formed by falling levels of a reservoir in Ohio
Primary succession would take place on all of the following EXCEPT…?
Answer: B
Invasive Species What is an invasive species?
(1)nonnative to the ecosystem under consideration, and(2)whose presence causes or is likely to cause economic or environmental harm, or harm to human health
Terminology
Invasive : Alien, nonnative, exotic, naturalized, weed
Native: Indigenous Endemic – species lives only in one specific area
Costs of Invasive Species • Economic >$120 billion annually in the U.S.
• Health Introduced pathogens and diseases Example: Dutch Elm Disease,, West Nile Disease
• Biodiversity - 2ndmost important cause of loss of biodiversityIn the U.S., >1/2 of the species listed as threatened or
endangered are at risk due to competition with or predation by nonnative species
• Ecological systems in disturbance
Invasive Species - SuccessCharacteristics of Invasive species that enable them to thrive in new environments: •Generalist species•Excellent dispersal mechanisms allowing it to spread•R-selected/r-strategist example: many offspring produced, early onset of reproduction, frequent reproduction •Superior defenses against predators in new environment (Novel weapons hypothesis – ex: Plants….chemicals exuded in the native range are benign to surrounding (co-evolved) plants. In new areas these compounds are often toxic ex: Cane Toad)
•Superior skills as a predator in new environment
Characteristics of new environment that enable them to thrive…•Lack of natural predators, parasites, pathogens to keep population in check
Invasive Species – Success
Invasive Species – most common crimes
• Compete for resources with native species
• Prey on native species
Mechanisms for Spread • Within 2-3 years – spread to all 5 Great Lakes, Hudson
River, Illinois River to Mississippi River• By 1994 colonized waters in 19 US states and 2 Canadian
provinces• Main Reason – Recreational activities…Transport of boats
or boat trailers with mussels attached• Flooding of isolated lakes with floodwater containing
mussels• Transport by animal vectors….example: brought with fish
used to stock lake waters• Building canals between infested and noninfested lakes
Impacts Economical Impacts: •Clogging up water intake pipes•Large densities - Damage boat engines, docks, fishing gear, and sink buoys ships use for navigation
Ecological Impacts • Consume entire population of phytoplankton –
diminish other populations that compete for this resource
Ex: zooplankton, fish, other native mussels• Disrupt food chains • Suffocate native mussels – attaching to their shells
Ecological Effect • Benefit bottom dwellers of lake – create lake clarity
by consuming algae….more sunlight available to bottom dwelling plants for photosynthesis
• Wastes – more organic material at bottom of lake • Increased populations of “visual feeders” – improved
ability to “see” prey…ex: water fowl…certain fish species
• Alter water chemistry – through filtering and digestion of their food, also shells store minerals from the water
Methods that might be used to prevent spread?
• Cleaning of boats before transport or launch• Refrain from building connecting canals between
waterways• No catching or distributing mussels for use as bait or pets
in aquariums• No transporting of water from one lake to the next (bait
buckets…should be dumped on land when possible• Education to discourage practices causing spread • Study its behavior and biology – determine best strategies
for controlling spread
Biological Control
Method of decreasing population of invasive species by re-introducing some of the natural enemies that exert control on it (using live organisms)
Cane Toad – biological control gone bad
• Introduced in Australia in 1935 as biological control against Greyback beetle that were destroying sugar cane crops
• Native to South and Central America• Had been successfully used as biological control against
beetles in Hawaii • Lack of research on Cane Toad was at fault: 1. Sugar reaches heights of 6-8m, beetles feed on tops of
plant….toads unable to reach that high 2. Timing – beetles are out in daytime, toad feeds at night 3. Wrong habitat – Sugar Cane fields much drier than
native habitat of toads…toads need wet conditions….quickly moved from sugar cane fields to moister areas.
Spread of Cane Toad…1. Generalist species – can live in a variety of habitats, eat a
variety of foods2. Predator to many native species (eats them)3. Competition – Out competes native species for food and
breeding sites4. R- selected species – can lay 8,000-30,000 eggs at a
time....Australia’s native frogs only lay 1,000-2,000 eggs per year.
5. Poisonous – few predators have resistance to this venom6. No successful predators or agents in reducing their
population
Biological Control Success Stories Cottony Cushion Scale
• The insect sucks the phloem sap from the leaves, twigs, branches, and trunk from California citrus trees
• Named after the white cottony secretion it produces • First discovered in citrus groves in 1868• Natural predator Ladybird beetle • 1988 514 beetles introduced into citrus groves of
California…by 1890 all infestations of cottony cushion scale were eliminated