Transcript lect14cut
Species Interactions: Competition (Ch. 13) Competition (Ch. 13) • Definition: – Individuals attempt to gain more resource in limiting supply – (-,-) interaction: both participants get less • Intraspecific: Within species. • Interspecific: Between species. Competition • Interference Competition: – Individuals interact with each other • Resource (Exploitation) Competition: – Individuals interact with resource • Ex: alfalfa Competition: plants Competition: plants • Ex: alfalfa • Type competition? Competition: plants • Self-Thinning Rule: Biomass increases, mortality reduces density (size per survivor increases) intraspecific competition Note log: log scale Can plants do Interference? Interference competition: plants • Allelopathy: Plant makes chemical reduces growth/survival (other plant) • Ex, Salvia (sage) Animal Competition • Plant hoppers (insects: Homoptera) – Tap plant vascular tissue – Experiment: density vs insect performance measure – Type competition? Intraspecific competition: animals • Wood lice (isopod): Terrestrial crustacean Intraspecific competition: animals • Study: high density & high mortality – Adding more food: no increase survival – Why?? Hint…. Intraspecific competition: animals • Study: high density & high mortality – Adding more food: no increase survival – Why?? Interspecific competition • Classic experiments: Gause – Demonstrated resource competition with Paramecium caudatum & Paramecium aurelia Q: Why was Gause always in a hurry?? Paramecia Lab Experiments • Grown alone: K determined by intraspecific competition. dN/dt = rmaxN (1-N/K) Paramecia Lab Experiments – Together, P. caudatum declined. Flour Beetle Experiments • Classic experiments: Tribolium beetles (eat grain) – Park studied T. confusum and T. castaneum Flour Beetle Experiments • Grown separately… • Grown together: interspecific competition Field Experiments • Connell: barnacles • Removal experiment Field Experiments • No effect Balanus removal upper intertidal Competition Between Barnacles • Big effect middle intertidal Barnacles • Chthamalus zonation also involved predation (lower intertidal) • Tolerance, competition, predation involved! Competition of Small Rodents • Brown studied competition: Chihuahuan Desert – Removal experiment Competition of Small Rodents • Chihuahuan Desert. Competition of Small Rodents • Chihuahuan Desert. Pocket mouse (Perognathus) Competition of Small Rodents • Chihuahuan Desert. Grasshopper mouse Why does competition occur? • Overlap in resource use: niche overlap • Niche: Summarizes environmental factors that influence growth, survival, and reproduction. Niche (review) • Hutchinson defined niche as: – n-dimensional hypervolume • n = number environmental factors important to survival and reproduction – Fundamental niche - hypervolume – Realized niche - includes biotic factors (like competition!) Niche overlap • Gause: Principle of Competitive Exclusion – 2 species with identical niches cannot coexist indefinitely (niche overlap important!) Mathematical Models • Scientific models: – Abstractions/simplifications – Provide insights into nature Example (male) model… Lotka Volterra • Recall Logistic Growth Equation: – dN/dt=Nrmax (1-N/K) – Same as: – dN/dt=Nrmax (K-N)/K Lotka Volterra • (K-N)/K contains effects intraspecific competition • K reflects resource availability • N reflects resource use Lotka Volterra Equations • Competition between 2 species. • Customize Logistic Growth Eqn. for sp. 1: • dN1/dt=N1rmax1 (K1-N1)/K1 – – – – dN1/dt=rate of change population sp. 1 N1=number sp. 1 individuals rmax1 =intrinsic rate of increase sp. 1 K1=carrying capacity for sp. 1 Lotka Volterra • dN1/dt=N1rmax1(K1-N1)/K1 • (K1-N1)/K1 includes resource use sp. 1 • How subtract resource use sp. 2 from that available to sp. 1? Imagination Lotka Volterra • Convert resource use individual sp. 2 into sp. 1 units – Make “conversion factor” (12) – Multiplied by N2 expresses sp. 2 resource use as sp. 1 individuals • 12 N2 = resources not available to sp. 1 because used by sp. 2 • (K1-N1- 12 N2) expresses total resource availability for sp. 1 Lotka Volterra • Equation: • dN1/dt=N1rmax1 (K1-N1- 12 N2)/K1 • Population growth rate species 1 • No sp. 2: Logistic Growth Equation for sp. 1 – dN1/dt=N1rmax1 (K1-N1)/K1 • Lots sp. 2, dN1/dt small Lotka Volterra • dN1/dt=N1rmax1 (K1-N1- 12 N2)/K1 • Alpha: competition coefficient. Expresses effect individual sp. 2 on individual sp. 1 • If 12>1, individual sp. 2 has greater effect than individual sp. 1 Lotka Volterra • Equation for sp. 2: • dN2/dt=N2rmax2 (K2-N2- 21 N1)/K2 • Note: 21 and 12 usually not equal: competition asymmetric Competition and Niches • Interspecific competition should lead to directional selection (reduce niche overlap) • Character displacement: shift in species traits Character Displacement • Compare allopatric (non-overlapping) & sympatric (overlapping) populations Character Displacement • Ex, Galapagos finches • Geospiza fortis & Geospiza fuliginosa Character Displacement • Shift documented Character Displacement • Many cases suggested: hard to prove competition cause! Competition and Conservation • Alien invasive species: may be better competitors Competition and Conservation • Ex, mud snails: Cerithidea californica (native) vs. Batillaria attramentaria (introduced) “Homeboy” snail Asian invader Competition and Conservation • Lots of alien snails…. Asian invader Competition and Conservation High densities reduce food supply (diatoms) Competition and Conservation Alien growth rate high Competition and Conservation • Population models: competitive exclusion in 5570 years • Who cares? – Native snail host of 17 species trematodes (mollusk parasites): live only in Cerithidea californica! Exploitation: Predation, Herbivory, Parasitism, and Disease (Ch. 14) 5 main types of interactions among species: Effect on Effect on species A species B Competition - - Predation + - Parasitism + - Commensalism + 0 Mutualism + + Type of interaction Symbioses There are several types of exploiters! • Exploitation: Interaction that enhances fitness of one while reducing fitness of another • (+,-) interaction. Minus to “prey/host” • Plus to: – Predators: Kill and consume MANY other organisms – Grazers: Consume MANY, kill FEW or none(Herbivores generally) There are several types of exploiters! • Plus to: – Parasites: Live in/on ONE or FEW host(s) and reduce host fitness (usually do not kill host) • Parasitoid: insect larva that consumes host (usually much smaller than host) • Pathogens: induce disease (debilitating condition)