The position of an organism in its environment and how it interacts with the environment
Niche
Summary of tolerances and resources needed to maintain a viable population
Fundamental niche
The theoretical volume of where a species could survive
Realised niche
The smaller volume where the species actually does survive due to competition from other species
Abundance will vary within the niche, with higher numbers in conditions closest to the optimum
Niche breadth
How broad or narrow a niche is, i.e. how specialised or generalised a species is
Prey size in lizards
Narrow niche = 36mm
Broad niche = 243mm
Interspecific competition
When under competition for a limited resource, individuals of one or both species will suffer decreased growth, fecundity, or survivorship
Exploitation
Indirect competition, e.g. diatoms competing for limited silicate
Interference
Direct competition, e.g. barnacles competing for space
Niche differentiation will reduce, but not remove, competition between species
Gause'saxiom
The competitive exclusion principle - no two species can co-exist in a stable environment without niche differentiation
If exploitation of niches by species overlap heavily, there will be strong competition, leading to either one species being competitively excluded or the two being driven apart to reduce competition
Partitioning in space
Macaranga trees partitioning light levels
Partitioning in time
Mantis religiosa and Tenodera sinensis having life cycles 2-3 weeks out of phase
Sympatric, closely related species can only coexist if there is a minimum difference between them allowing for niche separation
Many species are more different to their relatives when sympatric rather than allopatric, suggesting increased selection for differentiation
