exploitation in diatoms (Asterionella formosa vs. Synedra ulna)
- both species use silica as a resource
- when alone, both species reach carrying capacity, but S. ulna reduces silica to lower levels than A. formosa
- when together, silica is lowered to levels below A. formosa can use; S. ulna reaches carrying capacity, but A. formosa density slowly lowers
competitive exclusion principle
two or more species cannot coexist indefinitely while using a single, relatively scarce, resource in the same way
fundamental vs. realized niche size
- many species have smaller realized niches, due to species interactions that limit where they can exist
- positive interactions can expand a species range (e.g. lichen = fungi + algae), whereas negative interactions can lessen a species range (e.g. yellow-headed blackbirds limit the range of red-winged blackbirds)
symbioses
- close, prolonged mutualisms between two species; often with one species providing habitat for other species to live in
- e.g. pee aphids and Buchnera bacteria; bacteria produce amino acids for aphids, and aphids are the host environment for Buchnera, as they can’t live on their own
obligate mutualism
a mutualism in which at least one of the interacting organisms cannot survive without the other organism
predator-mediated coexistence
predation can reduce the number of stronger competitors, leading to coexistence with lesser competitors it would usually exclude
five types of species interactions
- competition: individuals use the same limiting resource in the same way, resulting in lower fitness for both (-/-)
- predation: one individual benefits by consuming all of another organism (+/-)
- grazing/parasitism: one organism benefits by consuming part of another organism (+/-)
- mutualism: two interacting individuals both experience a net benefit from an interaction (+/+)
- commensalism: one individual benefits from an interaction, and the other neither benefits nor is harmed (+/0)
two types of competition
- exploitation (resource competition): when one species consumes a resource shared between itself and its competitors, making it less available for others to use (two species compete indirectly)
- interference (contest competition): when one species restricts another species’ access to a limiting resource, which can involve antagonistic interactions, or one species excluding the other from a space (two species compete directly)
facilitation
- when one species benefits from another species indirectly, often through its impact on a third species or on the environment itself
- e.g. nurse plants shade the ground in arid habitats, decreasing water loss by evaporation and increasing soil fertility; this increases seed germination and seedling survival rates for other plants in the area
mite experiments, and the impacts of predation
- herbivorous (prey) mites and carnivorous (predator) mites are placed on oranges
- when mites can’t disperse, predatory mites eat all of the prey mites, and then they starve to death; both species disappear
- when herbivorous mites can disperse, there is a stable cycle in which prey have refuges where they can hide and increase in numbers
- predator and prey populations are linked in lab settings, but in nature other factors can override this, due to interactions between more than one species
characteristics of mutualism
- more common in harsh environments where species may struggle to persist
- by-products benefits: benefits of mutualism outweigh costs of mutualism
- can involve protection from predators/competitors, or increased access to resources
- tightly-linked mutualisms can lead to co-evolution (e.g. hummingbird bills have co-evolved with flower shape)
phylogenetic niche conservatism
similarities in aspects of the niches of closely related species, due to their shared evolutionary history (e.g. different woodpecker species all have adaptations for drilling holes into bark to find insects)
three types of consumption
- “true” predation: one organism consumes another organism or organism-to-be; prey die quickly, many prey are attacked (e.g. wolves eat hares, squirrels eat seeds (baby trees))
- grazing (herbivory): one organism consumes small parts of another organism; prey don’t die quickly/at all, many prey are attacked (e.g. caterpillars live on a single tree)
- parasitism: one organism consumes small parts of/steals resources of another organism that it lives in close association with; prey don’t die quickly/at all, very few prey are attacked (e.g. mosquitoes suck on humans’ blood)
R* rule
when two species compete for a single limiting resource (at constant population densities), the species that can persist on lower amounts of that resource will win the competition
ways competitors can coexist
- stronger competitors are harmed by negative interactions and/or weaker competitors are benefited by positive interactions
- competitors share (niche partitioning) by dividing resources, habitat, or timing of key life events (e.g. different mosquito species reproduce in different months)
- resources can vary, favouring different competitors in different places/during different times
amensalism
when one species is not affected by competition, but wins outright (e.g. a stampede trampling plants)
intraspecific vs. interspecific competition
intraspecific competition: competition among individuals of the same species
- density-dependent (competition for resources)
- once the population reaches carrying capacity, resources become scarce, causing fertility to decrease, and mortality to increase (births = deaths)
interspecific competition: competition between individuals of different species
- e.g. Kudzu covers over trees, interfering with their ability to photosynthesize by shading them out
character displacement
- divergence in characteristics of two otherwise similar species as a result of competition in sympatry (i.e. changes due to natural selection)
- only occurs in sympatric populations (occupy the same geographic area), not allopatric populations (occupy different geographic areas)
- e.g. Darwin’s finches and beak sizes
fundamental vs realized niche
- fundamental niche: the full range of climatic conditions and food resources that permits a species to survive (absence of interactions with other species, no competition)
- realized niche: the fundamental niche in the presence of negative species interactions (i.e. interspecific competition or predation) and positive species interactions (i.e. mutualism or competition)
niche
- combination of the physical habitat of a species, and its ecological role in that habitat
- determined by both abiotic and biotic factors that affect the species
community
- interacting populations of different species found in the same place/time
- inter-relationships govern the flow of energy and nutrient cycling within the community
