Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download BIOL 410 Population and Community Ecology
Document related concepts
Ecological fitting wikipedia , lookup
Unified neutral theory of biodiversity wikipedia , lookup
Biodiversity action plan wikipedia , lookup
Molecular ecology wikipedia , lookup
Habitat conservation wikipedia , lookup
Introduced species wikipedia , lookup
Latitudinal gradients in species diversity wikipedia , lookup
Island restoration wikipedia , lookup
Occupancyβabundance relationship wikipedia , lookup
Transcript
BIOL 410 Population and Community Ecology Competition Lotka-Volterra models Lotka-Volterra models β’ Logistic population models ππ1 πΎ1 β π1 β πΌπ2 = π1 π1 ππ‘ πΎ1 β’ Solutions at equilibrium π1 = πΎ1 β πΌπ2 ππ2 πΎ2 β π2 β π½π1 = π2 π2 ππ‘ πΎ2 ππ =0 ππ‘ π2 = πΎ2 β π½π1 β’ Equilibrium population values π²π β πΆπ²π π΅π = π β πΆπ· π²π β π·π²π π΅π = π β πΆπ· Can species invade? β’ Species 1 can invade when πΎ1 πΎ2 β’ Likewise, species 2 can invade when 1 πΎ1 > π½ πΎ2 >πΌ Interspecific competition Population Size β Species 2 (N2) β’ Can species 1 invade? Isocline for species 1 Isocline for species 2 π²π πΎ1 >πΌ πΎ2 π²π πΆ π²π Invade? K1 K2 Ξ± 100 200 >0.5 No 100 50 >2 No π²π π· Population Size β Species 1 (N1) Ξ² Interspecific competition β’ Can species 1 invade? πΎ1 >πΌ πΎ2 Population Size β Species 2 (N2) Isocline for species 1 Isocline for species 2 π²π πΆ K1 K2 Ξ± 100 50 <2 Yes 100 200 <0.5 Yes 1 πΎ1 < π½ πΎ2 π²π π²π π· Invade? Ξ² Exclude? K1 K2 100 50 >0.5 Yes 100 200 >2 Yes π²π Population Size β Species 1 (N1) Ξ± Ξ² Four outcomes of competition Stability? Invasion capability? 1 πΎ1 < >πΌ π½ πΎ2 Species 1 can invade Species 1 excludes 1 πΎ1 > >πΌ π½ πΎ2 Species 1 & 2 can invade Stable coexistence 1 πΎ1 > <πΌ π½ πΎ2 Species 2 can invade Species 2 excludes 1 πΎ1 < <πΌ π½ πΎ2 Species 1 & 2 can not invade Unstable equilibrium Model Assumptions β’ Logistic model assumptions β no age or genetic structure, no migration, no time lags... β’ Additional Assumptions: 1. Resources are in limited supply 2. Competitive coefficient (Ξ±/Ξ²) and carrying capacities (K1 / K2) are constants. 3. Density dependence is linear Are Lotka-Volterra dynamics observed? β’ Stable coexistence between competing species? β’ Competitive exclusion when species compete? Competitive exclusion principle β’ Gause's Law of Competitive Exclusion β In a stable environment, two species cannot coexist if they use exactly the same resources β’ Gause (1934): If two species, with the same niche, coexist in the same ecosystem, then one will be excluded from the community due to intense competition. β’ The niche of a species consists of its role in the ecosystem (herbivore, carnivore, producer etc), its tolerance limits (e.g. soil pH, humidity) and requirements for shelter, nesting sites etc etc, all varying through time. Principle of Competitive Exclusion β’ Complete competitors can not co-exist β’ Two species with extremely similar ecology and physical attributes will have high competitive effects on each other (Ξ± and Ξ² are each close to 1) INTERSPECIFIC COMPETITION β INTRASPECIFIC COMPETITION β’ As species diverge to utilize less overlapping resources (Resource Partitioning), their competitive effect on each other is lessened (Ξ± and Ξ² are both closer to zero). INTERSPECIFIC COMPETITION < INTRASPECIFIC COMPETITION Competitive exclusion Georgyi Frantsevitch Gause β Russian microbiologist β Paramecium growing in controlled environment (1934) Competitive exclusion β’ Gause (law of competitive exclusion) Competitive exclusion β’ Competition between freshwater diatoms β Asterionella formosa β Synedra ulna β’ Silica skeleton β’ Silicate is the limiting nutrient Competitive exclusion - Controlled experiment - Single limiting resource Competitive exclusion Exploitation competition or Lower minimum resource needs? Competitive exclusion β’ Ecological examples? β’ Red and Grey squirrels in Brittan β Red squirrels: native to European boreal forests β Grey Squires: native to NA hardwood and mixed forests. Red and Grey squirrels Red and Grey squirrel competition β’ Grey squirrels introduced in ~30 sites between 1876 and 1929 β’ Red squirrel decline β’ Completive exclusion β’ Disease, disappearance of hazel coppices and mature conifer forests Stable coexistence β’ Non-static relative competitive ability β Competition coefficients variable through time β Competition coefficients variable through space β’ Non-identical resource needs β Avoid competition in space β Avoid competition in time β Use different resources (use resources differently) Competition coefficients variable through time H. contortus Perennial tussock grass U. mosambicensis Buffalo grass Over time, access to resources can change- shifting the competitive balance between two species Competition coefficients variable in space Milk thistle Italian thistle Woolly dastaff thistle The competitive balance among species can be shifted along resource gradients Gradients often represent a spectrum of stress tolerance and competitive ability Phosphate Diatom competition Silica Resource partitioning Resource partitioning β’ Partitioning of resources, differentiation of realized niches β Potential niche β Fundamental niche β Realized niche Niche differentiation and competitive exclusion Chthamalus β’ tolerates a broad range of exposure to air β’ Poor space competitor Balanus β’ cannot tolerate long exposure to air β’ but in lower intertidal, is very aggressive - pries off Chthamalus. Niche partitioning ~ trade-offs Niche differentiation β’ Using resources differently β Accessing resources differently β Competing for resources differently Niche β’ Niche is a multidimensional β’ An organisms niche is defined by many features of the environment dictate whether an organism is successful β’ i.e. likelihood that two organisms share exactly the same niche space is potentially less β’ Therefore, if two organisms share exactly the same requirements for some resource or environmental feature- they can still coexist as long as some other feature differs. Niche differentiation Competitive exclusion principle (restated) If two competing species coexist in a stable environment, then they do so as a result of niche differentiation. If, however, there is no such differentiation, then one competing species will eliminate or exclude the other. Begon et al. 1996 Ecology: From Individuals to Ecosystems Spatial niche differentiation Spatial niche partitioning β’ Caribbean Anolis lizards β Forage in the same place (thickness of branch) β Forage on the same prey items (prey size) Competition β’ Competitive exclusion β When niche is very similar and constant β’ Stable coexistence β Niche differentiation β Dynamic environment (dynamic competition coefficients) Niche differentiation β’ Realized through changes in biology β’ Niche separation between species, and sexes Intraguild Predation β’ Occurs when one species not only competes with its heterospecific guild member, but also occassionally preys upon it. β’ Species 1 β Competitor & Occasional Predator β’ Species 2 β Competitor & Occasional Prey Intraguild Predation β’ Species 1 β competitor and predator β’ ππ1 ππ‘ = πΎ1 βπ1 βπΌπ2 π1 π1 πΎ1 + πΎπ1 π2 β’ Species 2 β competitor and prey β’ ππ2 ππ‘ = πΎ2 βπ2 βπ½π1 π2 π2 πΎ2 β πΏπ1 π2 Intraguild Predation and Isoclines β’ Species 1 Isocline - Number of species 2 required to Population Size β Species 2 (N2) drive species 1 to extinction EXCEEDS K1/Ξ±, as Species 2 losses individuals to predation. (Isocline rotates, but K1 and K1/Ξ± do not change) π²π πΆ π²π Population Size β Species 1 (N ) Intraguild Predation and Isoclines β’ Species 2 Isocline - Number of species 1 required to Population Size β Species 2 (N2) drive species 2 to extinction is LESS THAN K2/Ξ², as Species 1 both competes and preys on species 2. (Isocline rotates, but K2 and K2/Ξ² do not change) π²π π²π π· Population Size β Species 1 (N1) Intraguild Predation and Isoclines Population Size β Species 2 (N2) β’ Adding this dynamic can now change the anticipated outcomes of state-space models π²π π²π πΆ π²π π²π π· Population Size β Species 1 (N1)
