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Tilmans R* Theory

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Mar 1, 2020

Cards (49)

Section 1

(49 cards)

Tilmans R* Theory

Front

1. mechanistic- based on how species consume specific limiting resources 2. two species compete exploitatively for single limiting resource, outcome of competition is determined by which species is able to reduce that single limiting resource to the lowest level at equilibrium 3. level to which a species lowers a limiiting resource when grown in monoculture is that species R* 4. species with the lowest R* wins 5. species must reach a biomass or population equilibrium before measuring R* 6. equilibrium point takes into account mortality rate 7. habitat specific resource supply rate; does not suddenly increase or decrease with time 8. R* is the level where population growth through time exactly balances loss through all agents of mortality

Back

succession

Front

the change in the dominant plant species at a given location through time

Back

Apparent Competition example

Front

could be generated if one species facilitates the enemy of another species (Ex. several species of shrub have bare soild around them due to small rodents that eat plant seeds)

Back

Physiological differences

Front

differing ability to tolerate dessication at low tide during warm weather and calm seas. Thus, Chthamalus occurred higher in the zone because it could stand drying out at low tide.

Back

Plasticity

Front

the capacity of an organism to vary morphologically, physiologically, or behaviorally as a result of environmental fluctuations

Back

genet

Front

all of the ramets, connected or not that make up a clone

Back

Interference competition

Front

when competitors do not immediately consume resources but defend them; direct competition

Back

Tilman critical factors

Front

1. resource that limits population growth: nitrogen 2. mechanism underlying competition: reduction of nitrogen? 3. trait that confers competitive ability: allocation to roots?

Back

Guild

Front

a group of similar species using similar resources in similar ways

Back

Plants are autotrophs

Front

therefore resources are essential, not substitutable (compared to mountain lion who can eat a rabbit or a deer)

Back

Equilibrium

Front

the size of the population of organisms is constant through several generations or growing seasons

Back

Tilman's resource reduction model

Front

the winner in a bout of competition was the best competitor for a shared limiting resource

Back

Interspecies competition

Front

competition between different species, typically depresses populations of both competitors

Back

Exploitative competition

Front

competition in which individuals consume and drive down the abundance of a resource to a point that other individuals cannot persist, indirect competition

Back

plants are sedentary

Front

therefore they respond to local resource levels and interact locally primarily with their neighbors; spatial pattern becomes potentially very important

Back

ramet

Front

unit of a clone that can live an independent existence when separated from the rest of the clone

Back

The pattern in Connell study

Front

two barnacle species in Scotland occur at different locations within the intertidal zone; smaller species, Chthamalus stellatus, occurs higher in the intertidal than the other species, Balanus glandula

Back

Resource

Front

any substance or factor that is consumed by an organism and that supports increased population growth as its availability in the environment increases

Back

Cause of the pattern Connell experiment

Front

physiological tolerance of Balanus demonstrated that high mortality during periods of calm weather when tides did not penetrate near shore

Back

Tilman Experiment #1

Front

growing plants in monoculture to quantify R; grew all 5 species to reach biomass equilibrium and measured soil nitrogen leneath plots. Schiz has lowest R and Agrostis the highest R*

Back

Goldberg's equivalence of competitors model

Front

the winner was the larger individual

Back

Aggressive Interactions

Front

an effective form of interference competition (Ex. long-legged ants blocking red harvester ants nests so they can't forage for the same food)

Back

Competitive exclusion principle

Front

two species cannot coexist indefinitely when they are both limited by the same resource

Back

Importance of interspecific competition in natural communities

Front

1. competition is prevalent and plays role in determining the distribution, abundance, and diversity of species 2. competition is typically highly asymmetric; one species has strong effect on subordinate species 3. field experiments run over many years and are the most powerful tools for evaluating influence of interspecific competition 4. field experiments only identify that competition is occurring and how this effects the relative abundance of species 5. importance of interspecific competition varies from community to community; plays important role in sessile organisms 6. competition is likely to be more important in determining interactions among species within the same guild

Back

Pattern #1 (Tilman)

Front

through 50 years of succession in grassland in Minnesota, Tilman identifies a consistent pattern of dominance by 5 different species of grasses

Back

Allelopathy

Front

chemical competition most frequently reported among plants; typically by toxic substances (ex. production of flammable oils by eucalyptus trees in Australia that promote fires to kill seedlings of competitors)

Back

General theory of interspecific competition

Front

1. the resource that limits population growth in a habitat 2. the mechanism underlying interspecific competition 3. the trait that confers competitive ability

Back

Pattern #2 (Tilman)

Front

the different types of grasses allocated more to roots later in succession

Back

Related species

Front

competition is most intense between related species because they have similar traits and consume similar resources (ex. acidic soils and bedstraw)

Back

Tilman Experiment #2

Front

paired competition experiments to see if the R value for each species predicted the outcome of competition; the species with the lower R won in competition

Back

Goldberg & Werner

Front

all species have equal competitive ability and bigger individuals are better competitors than smaller individuals; size of individual is more important than the identity of the individual

Back

Consequence

Front

huge differences in size among individual plants are common

Back

Implications of clonality in plants

Front

ramets in rich environments can feed ramets in resource poor environments; ramets are typically genetically identical; ramets within a clone may compete or subsidize on another and this may alternate; clonal plants may typically have an advantage over non-clonal plants

Back

Competition

Front

any use or defense of a resource by one individual that reduces the availability of that resource to other individuals

Back

Biomass

Front

the weight of all plants in a given area

Back

Tansley's conclusions

Front

No one knows why similar species can out compete one another

Back

Combinations of competition example

Front

temperate forests have an increase in abundance of white-tailed deer has reduced the abundance of tree seedlings. Seed predation affected one species while deep shade affected red maple seedlings.

Back

Conditions

Front

not consumed by organisms; not resources, includes pH or temperature

Back

Competing for multiple resources

Front

two species may be able to coexist when each is better at persisting at low levels of different resources, they are better at using two different resources

Back

Intertidal study by Joe Connell 1961

Front

demonstrates the role of interspecific competition in creating patterns within a natural marine community; reveals the complexity of factors that control species distributions

Back

What Tilman knew

Front

1. Nitrogen limited population growth for all grass species 2. the species that occurred early in succession produced enormous quantities of long-lived easily dispersed seeds relative to later successional species 3. allocation to roots gave a competitive advantage when nitrogen was limiting 4. allocation to seeds gave an advantage when a site was unoccupied

Back

Allelopathy Example

Front

sage (salvia) use chemicals to inhibit the growth of other vegetation, grasses separate them from adjacent grasses, toxic chemicals (terpenes)

Back

Apparent Competition

Front

two species can share a resource an have negative effects on each other through an enemy, such as a predator, parasite, or herbivore (Ex. ring-neck pheasant can survive parasite that gray partridge cannot and so they out compete the partridge)

Back

Intraspecific competition

Front

competition between members of the same species, reduces resources in a density-dependent manner

Back

Barnacles

Front

marine crustacea that are sessile as adults but have free swimming larval phase

Back

Intertidal zone

Front

the shore zone between the highest and lowest tides

Back

Apparent competition

Front

when two species have a negative effect on each other through an enemy - including a predator, parasite, or herbivore

Back

Tilman Hypotheses

Front

1. replacement of species in time during succession was caused by species that are better at getting nitrogen due to more roots 2. mechanism determining outcome was the ability to reduce nitrogen levels in the soil

Back

Clonal plants

Front

individual units or stems in a population that are derived vegetatively (asexually) from a single parent; made up of ramets and genets

Back