ch 14: interspecific competition

interspecific competition

competition between members of different species

- predation (+/-)

- parasitism (+/-)

- mutualism (+/+)

- competition (-/-)

examples of possible interspecies interactions

- darwin based his idea of natural selection on competition, the "struggle for existence"

- competition is the major driving force behind species divergence and specialization

- interspecific competition can influence survival and reproduction

describe interspecific competition and natural selection

exploitation and interference

two forms of interspecific competition

occurs when species indirectly interact with one another but affect the availability of shared resources

what is exploitation

results when species directly interact and prevent others from occupying a habitat or accessing resources within it

what is interference

- species 1 will win

- species 2 will win

- uncertainty (one species will win, but it cant predict which one)

- coexistence (species learn to live together)

what are the possible outcomes of interspecific competition between 2 species

- logistic growth (regulating)

- deltaN/deltaT= rN(1-N/K)

what determines the outcome of interspecific competition

population size of species 1

what does N1 represent

population size of species 2

what does N2 represent

the carrying capacity of species 1

what does K1 represent

the carrying capacity of species 2

what does K2 represent

the per capita effect on species 1, by species 2

what does alpha represent

the per capita effect on species 2, by species 1

what does beta represent

=r1N1(K1-N1-alphaN2)/K1

how would change of species 1 be calculated

=r2N2(K2-N2-betaN1)/K2

how would change of species 2 be calculated

species 1 will increase

what does it mean if K1-N1/K1 is higher than alphaN2/K1

species 2 will decrease

what does it mean if K2-N2/K2 is lower than betaN1/K2

zero growth isocline

a line on a graph representing the sizes of a predator and a prey population, or of competing populations, designating points at which the growth rate of one of the populations is zero

Lotka-Volterra Equation

a mathematical description of the relationship between two species using the same resource

the species are not significantly impacting each other (very little competition)

- this would be what must happen for two species to coexist

- intraspecific population regulation factors are greater than interspecific factors

what does it mean when alpha and beta are low

- P. aurelia and P. caudatum were raised together in a test tube with a fixed amount of bacterial food - both are competing for the same resource/niche

- separately, each one has high population rates and thrives (K=200)

- in a mixed population, P. aurelia has a much higher population density than P. caudatum

- P. aurelia is still harmed, and the population numbers drop, but P. caudatum dies off

- P. aurelia wins in this situation

describe the example of interspecific competition with P. aurelia and P. caudatum

- 2 populations of diatoms of different species were mixed

- the 2 species (A. formosa and S. ulna) competed for silica (competing for the same resource/niche)

- at high silica levels, both species do good

- at lower silica levels, S. ulna is better at gathering silica than A. formosa

describe the example of interspecific competition with diatoms

competitive exclusion principle (Gause's Law)

ecological rule that states that no two species can occupy the same exact niche in the same habitat at the same time

- states that "complete competitors" cannot coexist

- if species 1 increases the least bit faster than species 2, then species 2 will become locally extinct

what is the competitive exclusion principle

- if they have the exact same resource needs (alpha and beta are very high)

- if there is enough time with a stable environment

what are the requirements for one species to outcompete the other

two species that live in the same place and have exactly the same ecological requirements (overlapping resource needs)

what are complete compeitors

complete competitors

two species that live in the same place and have exactly the same ecological requirements

non resource factors

affect population growth but are not consumable resources

species still compete for factors that are not consumable, and cannot be used up

- ex. temperature, soil, salinity, PH, humidity

how is competition influenced by non resource factors

when many different weeds out out seeds forming a seed bank, the temperature determines which ones germinate and grow

example of competition for non resource factors

- some species do better at different times during the year or different seasons

- in grass species in africa, the dominant species varied depending on the rainfall

- one species (U. mosambicensis) can survive better under dry conditions, while the other species (H. contortus) is a better competitor during rainfall

- these species switch dominance depending on the environment

how does variation in the environment influence competition

different species have different competitive abilities, which change in different environments

how does environmental change produce a gradient

- sierra nevada chipmunk species'

- the species have strongly overlapping food requirements and are competitors

- each species occupies a different altitudinal zone

- the species range is determined by aggressive exclusion (behavior) and ability to survive in a hostile environment

example of environmental gradient

- the least chipmunk lives at low altitudes and can occupy any altitudinal zone, but it not very aggressive

- the yellow pine chipmunk occupies the next zone up, but cant take the heat below

- the lodgepole chipmunk is very aggressive, but cant move up (too cold) or down (too hot)

- the alpine chipmunk is not very aggressive but is adapted to the cold

describe the sierra nevada chipmunk species'

full range of conditions and resources under which a species can survive and reproduce

- everything in an environment that an organisms could actually do with its characteristics

what is a fundamental niche

portion of the fundamental niche that the species actually exploits

what is a realized niche

fundamental niche

the full potential range of the physical, chemical, and biological factors a species can use if there is no competition from other species

realized niche

part of a species fundamental niche that it actually uses, limited by competition

- Typha species grown in pots without competition: one species grows at lower water depths, while the other grows at all water depths, with a wide range (fundamental niche)

- when grown in the wild with competitors: the species with a wide fundamental niche has a smaller range and only grows in higher water depths (realized niche)

example of realized and fundamental niche

similar species coexist by dividing available resources; each species has slightly different adaptations (feeding times, activity levels, and food sizes)

- more than one resource is often partitioned

what is resource partitioning

wild cats in israel each feed on different size prey to fit different niches and prevent competition

example of resource partitioning

resource partitioning

the division of environmental resources by coexisting species such that the niche of each species differs by one or more significant factors from the niches of all coexisting species

specific physiological, morphological, or behavioral adaptations

- these adaptations are considered the outcome of interspecific competition in the past

what does resource partitioning result from

- when on separate islands, the finches overlap in beak size

- when on the same island, they do not overlap

- the different species adapt different beak sizes to fit different niches

example of interspecific competition and resource partitioning in finches