Species Interactions Competition Ch 13 Competition Ch 13

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. d. N/dt = rmax. N (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: – d. N/dt=Nrmax (1 -N/K) – Same as: – d. N/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: • d. N 1/dt=N 1 rmax 1 (K 1 -N 1)/K 1 – d. N 1/dt=rate of change population sp. 1 – N 1=number sp. 1 individuals – rmax 1 =intrinsic rate of increase sp. 1 – K 1=carrying capacity for sp. 1

Lotka Volterra • d. N 1/dt=N 1 rmax 1(K 1 -N 1)/K 1 • (K 1 -N 1)/K 1 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 N 2 expresses sp. 2 resource use as sp. 1 individuals • 12 N 2 = resources not available to sp. 1 because used by sp. 2 • (K 1 -N 1 - 12 N 2) expresses total resource availability for sp. 1

Lotka Volterra • Equation: • d. N 1/dt=N 1 rmax 1 (K 1 -N 1 - 12 N 2)/K 1 • Population growth rate species 1 • No sp. 2: Logistic Growth Equation for sp. 1 – d. N 1/dt=N 1 rmax 1 (K 1 -N 1)/K 1 • Lots sp. 2, d. N 1/dt small

Lotka Volterra • d. N 1/dt=N 1 rmax 1 (K 1 -N 1 - 12 N 2)/K 1 • 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: • d. N 2/dt=N 2 rmax 2 (K 2 -N 2 - 21 N 1)/K 2 • 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 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)