Lecture 19 and 20- community ecology Flashcards
What is a community?
The species that live and interact in an area
What did detailed studies of plant distribution in Siskiyou mountains of oregon show?
Different combinations of plant species are found at different locations- species enter and drop out of communities independent over environmental gradients
What did Frederick Clements argue?
plant communities were tightly integrated “superorganisms.” Communities in similar areas would have the same species.
What did Henry Gleason argue?
plant communities are loose associations of species; each species was distributed based on its own
environmental requirements.
What can organisms be divided into based on the source of their energy?
Trophic levels
Autotrophic plants constitute a trophic level called…
(Photosynthesizers), primary producers
Heterotrophs that eat autotrophs are called…
herbivores or primary consumers
Organisms that eat herbivores are called…
Secondary consumers
Another type of trophic level is…
detritivores, decomposers.
Organisms that obtain food from more than one trophic level are called…
omnivores
A sequence of interactions in which a plant is eaten by a herbivore which in turn is eaten by a secondary consumer and so on can be diagrammed as a…
food chain
Food chains are interconnected to make…
a food web
Food webs help us to understand what?
The trophic interactions among organisms in an ecosystem
What are the 5 main ways that organisms interact with one another?
- Predation or parasitism
- Competition
- Mutualism
- Commensalism
- Amensalism
What are commensalism interactions?
Interactions in which one participant benefits and the other in unaffected
What are amensalism interactions?
Interactions in which one participant is harmed and the other unaffected
What effect do these 5 types of interactions have?
Influence population densities of a species, restrict range of conditions under which animals exist.
What does mutualism do?
Increases the range of physical conditions under which a species can persist
How do predator and prey population change?
They oscillate
Why do predator and prey populations oscillate?
Predators cause fluctuations in prey densities, growth of predator population lags behind growth of prey populations.
Give an example of predator-prey interactions.
Arctic lemmings (prey) and predators: arctic fox, snowy owl, jaegers, 3-4 year oscillations
Give another example of predator-prey interactions.
Canadian lynx (Lynx canadensis) and snowshoe hares (Lepus americanus) with 9-11 year cycle
How was it proven that oscillations are driven by both lynx predation and interactions between hares and their food supply?
They enclosed some areas with fences through which hares but not lynx could pass, and provided food in some areas.
what do predators also restrict?
The range of a species
What is the Australasian biogeographic region home to?
A group of birds-megapodes, also called mound builders- who do not incubate their eggs.
How do megapodes keep their eggs warm?
By laying their eggs in a mound of decomposing vegetable material
Megapodes are good dispersers. Why are they absent from all islands with Asian mammalian predators?
Unattended eggs
What are the two types of mimicry?
Batesian mimicry
Mullerian mimicry
What is Batesian mimicry?
Palatable species mimic unpalatable or noxious species
What is Mullerian mimicry?
Two or more unpalatable or noxious species converge to resemble each other.
When does Batesian mimicry evolve?
Only if the mimic evolves towards unpalatable/noxious species faster then that species evolves away (mimic is less common than the unpalatable species)
What two consequences do interactions between species have?
- Ecological consequences
- Evolutionary consequences
What do ecological consequences do?
Influence population densities
What do evolutionary consequences do?
Influence fitness of individual and lead to adaption.
What is reciprocal evolution between interaction species called?
Coevolution
What is a clear warning appearance of an individual called?
aposematism
What are the three classes in which members of the host population involved in microparasite-host interactions fall?
Susceptible
Infected
Recovered
What is the name of the bacterium that causes cholera?
Vibrio cholerae
How does cholera spread?
Ingestion of water containing V. cholerae
What does cholera bacterium do?
Toxin produced damages salt balance mechanisms
Why is competition widespread?
Because all species share resources
What are the two types of competition?
- Interference competition
- Exploitation competition
What is interference competition?
Interfering with activities
What is exploitation competition?
Reducing available resources
What are two types of competition between?
Intraspecific competition- among individuals of the same species
Interspecific competition- among individuals of different species
What does intraspecific competition do?
Results in reduced growth and reproductive rates of some individuals, exclude some from habitats, cause death of some
What does interspecific competition lead to if a superior competitor prevents all members of another species from using a habitat?
Competitive exclusion
What two sessile animals compete for space in intertidal zones?
Two species of barnacles
- Balanus balanoides
- Chthamalus stellatus
What is the distribution of the two species of barnacles?
Chthamalus live higher in the intertidal zone then Balanus with little overlap
What happened when one of the species of the barnacle was removed?
Both increased vertical range when the other was removed.
What was the conclusion of the barnacle experiment?
Chthamalus outcompete balanus in that zone- intertidal zonation is the result of competitive interaction.
How can a species restrict the range of another species?
By reducing the populations of shared prey to such low levels the other species cannot persist
What wasp was introduced to southern california?
Aphytis chrysomphali
Why was Aphytis chrysomphali introduced to Southern California?
To control outbreak of scale insects damaging crops- did not work
What wasp was introduced after Aphytis chrysomphali?
A.lingnanensis- higher reproductive rate, reduced population densities of Aphytis chrysomphali
Give an example of amensalisms.
Herd of mammals drinking water at a water hole trample and kill many plants
Trees drop dead leaves and branches, harming plants and animals below
Give an example of commensalisms.
Cattle egrets forage near mammals heads and feet to capture insects crushed by hooves and mouths.
Give a mutualistic relationship involving rhinos
Oxpeckers pluck blood-sucking ticks from skin of grazing mammals
Give an example of mutualistic relationships between fungi and plants.
Mycorrhizae
Nitrogen-fixing bacterium of genus Rhizobium
Give an example of animals and protists in a mutalist relationship
Corals and other marine organisms gain energy from photosynthetic protists
Termites have cellulose digesting protists in their gut
What are the two different niches that the barnacles could have occupied?
Fundamental niche- larger zone occupied when there is no competition
Realised niche- niche occupied when competitor is present.
What is a trophic cascade?
Change in the relative population of different trophic levels in a food chain that follows the addition or removal of a trophic level
Where can a trophic cascade be seen?
Wolf populations in the Lamar valley of yellowstone national park
What do wolves feed on in Yellowstone?
Pronghorn, mule deer, elk, bison, bighorn sheep, moose
When had wolves been extirpated from Yellowstone national park?
1926
Elk were culled until 1968 to prevent…
Them from exceeding the parks carrying capacity
What happened when wolves were absent with the elk?
They browsed aspen trees so intensely that no young trees grew after 1920
As well as stream side willow
What was the result of elk eating too much stream side willow?
Beavers were nearly exterminated
WHen were wolves reintroducted to yellowstone?
1995
Where are adult dragonflies more abundant?
Around fish-free ponds
What was less common around fish-free ponds?
Insect pollinators preyed on by dragonflies
What happened when there were less insect pollinators near fish-free ponds?
St Johns wort was visited less commonly by pollinators, and therefore produced less seeds
How do beavers cause trophic cascades?
Preferentially cutting down certain species of tree-alter vegetation composition
Building dams- creates meadows and ponds
What are organisms that create structures called?
Ecosystem engineers
What is a species that exerts an influence out of proportion to its abundance called?
A keystone species
What is the latin name of the keystone species of starfish from the textbook?
Pisaster ochraceus- lives in rocky intertidal zone on Pacific coast
What is the preferred prey of Pisaster orchraeceus?
Mussel Mytilus californianus
How does P.ochraeceus act as a keystone species?
Stops M.californianus crowding the intertidal zone, creating spaces for other species.
Give an example of a keystone species that isn’t a predator.
Fig tree species in tropical forests- fruit is ripe at times of year when food is scarce, fruit eating species depend on these figs.
What is a disturbance?
An event that changes the survival rate of one or more species in an ecological community
What happened in 1988 in yellowstone?
1/3 of the park was burnt in fires, created a mosaic of unburned patches, areas where herbs and shrubs were burned, areas were all trees were consumed.
What is a change in the composition of an ecological community following a disturbance called?
Succession
What are the two major types of succession?
Primary and secondary
What is primary succession?
Begins on a site lacking organisms
Where can primary succession be seen?
Changes in plant communities following the retreat of a glacier in glacier bay in Alaska over the last 200 years.
What has the melting and retreat of the glacier left?
Moraines- gravel deposits
What are the moraines closest to the glacial front populated with?
Bacteria, fungi, photosynthetic microorganisms
What do slightly older moraines have?
Lichens, mosses, shallow rooted herbs.
What is succession caused by?
In part by soil changes brought about by plants
What plants grow best on the most recently formed moraines and why?
Herbaceous plants such as Dryas and Alnus with nitrogen fixing bacteria in root nodules. Spruce can then outcompete them.
What can secondary succession begin with?
The dead parts of organisms- succession by fungal species
Describe the decomposition of pine needles of Pinus sylvestris.
Fungi of several genera aid in successive decomposition of needles, degradation produces from one group of fungi are food for growth of next
When is species richness greatest?
At intermediate levels of disturbance.
What is the name given to the theory that species richness is greatest at intermediate levels of disturbance?
Intermediate disturbance hypothesis
How does intermediate disturbance hypothesis work?
- High disturbance: only species with greatest dispersal and reproduction persist
- Low disturbance: competitively dominant species displace others.
How was the intermediate disturbance hypothesis tested?
Using boulders in the intertidal zone on californian beaches.
Why did medium sized boulders have more algae and barnacle species? How was the hypothesis tested?
- Small boulders moved more often by waves
- Glued small boulders to substratum- after 6 months, these had more species
What two things influence succession?
Facilitation and inhibition
How did Wayne Sousa test if species inhibit colonization by other speices?
Removed all organisms from some boulders and placed them in the intertidal zone, removed species during succession, final successor took over faster
What is species richness?
The number of species living in a community
Are species more or less rich at higher latitudes?
Less
Why are there more types of species in mountainous regions?
Because there are more vegetation types and climates.
Why are there less species richness on islands and peninsulas?
Differences in immigration and extinction rates
Species richness _______ with increasing productivity.
Increases
Why does species richness increase with productivity?
Number of individuals an area can support increases, larger populations, less extinction.
Why does species richness decrease when productivity surpasses a further point?
Interspecific competition become more intense, resulting in competitive exclusion
Why does species richness enhance productivity?
A richer mixture of species results in more complete resource usage
Changing environment- more likely to have a species adapted to new conditions- therefore more stable
How was the hypothesis that communities with many species should have higher productivity and stability than communities with few species tested?
Clear and plant pots with different numbers and mixtures of grass species. measure productivity and species composition of plots over 11 years.
What was the result of the plant pot experiment?
Productivity increases with species richness
Variation in productivity decreases with species richness
