Interspecific Competition and Mutualisms

purpose of the Lotka-Volterra Interspecific Competition Model

predicts whether 2 species can coexist, or if those 2 species compete, and which species outcompetes the other

r₁ and r₂ in the Lotka-Volterra model

intrinsic rate of natural increase for each species

K₁ and K₂ in the Lotka-Volterra model

carrying capacity of each species

α₁₂ in the Lotka-Volterra model

competition coefficient of species 2 on species 1

α₂₁ in the Lotka-Volterra model

competition coefficient of species 1 on species 2

zero isoclines

lines that connect all combinations of densities of species 1 and 2 that result in no population growth for either species

species 1 excludes species 2

species 1 is a strong interspecific competitor and species 2 is a weak interspecific competitor

species 2 excludes species 1

species 2 is a strong interspecific competitor and species 1 is a weak interspecific competitor

initial densities determine which species is excluded

for both species, interspecific competitors have a larger effect than intraspecific competitors

coexistence

for both species, intraspecific competitors have a larger effect than interspecific competitors

asymmetric interspecific competition

one species is negatively affected to a much greater extent than the other species

asymmetric competition in plants

taller species have first access to incoming light, while shorter species receive little to no light

asymmetric competition in insects

one species is more efficient in exploiting shared resources, dominant species are aggressive towards subordinate species, subordinate species show avoidance behavior, and dominant species modify the habitat to be less hospitable to the subordinate species

predation

individuals of one species kill and consume individuals of the other species

parasitism

individuals of one species consume tissues of the other species but don’t necessarily kill them

parasitoid

an insect lays egg inside the body of another insect and as the larvae develop, they consume their host

herbivory

animals consume plant tissues

compensatory ability

the ability to regrow tissue lost to herbivores and recoup lost reproduction

compensatory methods in plants

below-ground storage organs, redirecting resources from storage to regrowth, increase photosynthetic rate of undamaged tissues

prey refuges

allow prey to persist in spite of an efficient predator

spatial refuge

physical locations where prey are outside the reach of predators

refuges in size

life-stages in which a prey species is unmanageable by a predator

refuges in abundance

prey aggregations are either too numerous or too sparse for the predator to effectively hunt

refuges in dispersal ability

prey have superior dispersal ability to predators so they are always able to establish at least temporarily in locations where predators are absent

ecology of fear

presence of predators alters prey behavior, which affects prey fitness

mutualisms

interspecific interaction that increases the fitness of both species

facultative mutualism

increases the fitness of both species, but is not essential to the survival of either species

obligate mutualism

increases the fitness of both species and is essential to the survival of both species 

mycorrhizae

mutualism between the roots of plants and soil-dwelling fungi

arbuscular mycorrhizal fungi

mycorrhizae in which the fungus penetrates and exists inside the cortical cells of the root

arbuscles

branched fungal structures that are the site of nutrient exchange with the plant

hyphae 

filaments that grow among the root cortex cells and extend into the surrounding soil

vesicles

energy storage structures that exist within root cortex cells

ectomycorrhizae

mycorrhizae in which the fungus forms a sheath around the root and hyphae penetrate between, but not within root cortex cells

benefit to the fungus in mycorrhizae 

access to carbohydrate-rich root exudates

benefit to the plant in mycorrhizae

greater uptake of soil nutrients and water

cheating on mutualisms 

a species derives the benefits of mutualism without benefitting the other species in return

pollination by deceit

imitating the flower of a rewarding plant species, or imitating a mate/oviposition site for insect pollination