Lecture 5 - Niches and Distributions

niche

theoretical concept for a species’ role in an ecosystem, based on things like its role in a food web and/or its habitat preferences

there are a few, more specific ways to define niches: eltonian, grinnellian, hutchinsonian

eltonian niche

species’ role in relationships with other species

ex: a species that forages for food on the ground has a different eltonian niche than one that forages in treetops

**useful in small-scale field studies, where an ecologist might spend many hours observing animal behavior

grinnellian niche

the set of environmental conditions a species needs

for example: species that can’t survive freezing temperatures has a different grinnellian niche than one that lives in places that get snow

useful for big-scale studies like many in biogeography

hutchinsonian niche

all the ecological and environmental conditions a species needs

defined in a mathematical way

used in a lot of research based on statistics and theory

specialists vs generalists in niche space

specialist = species with a narrow niche, narrow environmental tolerances and specialized food needs

so if you have an axis, it’s narrow in terms of area

generalist = broad niche, broad environmental tolerances, uses a broad variety of resources

when comparing niches, is there a limit to how many axes we include?

no - there’s no limit to how many axes we include - we just can’t easily picture beyond 2 axes

**bigger area = generalist

smaller area = specialist

is it clear cut between generalist and specialist or is there a spectrum?

there’s a continuous spectrum of species from highly specialized to highly egenralized

geographic range

the distribution of a species in environmental space can be mapped onto geographic space

geographic range limits (the edges of a species’ distribution) are often set by the limits of environmental conditions they can tolerate (the grinnellian niche)

what things set range limits?

temperature - certain species can only exist in certain temperature ranges

precipitation - species need certain levels of precipitation to survive

population size relates to range size

species are often most abundant (most individuals per unit area, large local population size) at the center of a geographic range

species with larger geographic ranges often have more individuals overall, keeping other factors like body size constant

why?? - typically the optimal conditions for a species occur in the middle of both its environmental and geographic distribution

other factors that set range limits

species can’t always get to an area that might be suitable for them - dispersal barriers like river canyons block individuals from getting from where they presently live to where they could in theory also live

species affect where other species live - symbiosis and competition

ok so overall 3 main things that affect rangej

suitable abiotic (environmental) factors - temperature, precipitation,

geographic areas the species can get to - dispersal barriers

suitable community of interacting species - symbiosis, competition

**where these three things overlap in a venn diagram is the actual geographic range of a species

fundamental niche

full range of conditions that would be sufficient for a species to live, if there weren’t any restrictions from barriers or other species

**aka includes suitable abiotic factors

realized niche

range of conditions where the species can live, given the limitations from other species e.g. competition

ex: includes abiotic factors and suitable community of interacting species

competitive exclusion

competitive exclusion principle says that species with identical niches cannot exist in the same geographic region because one would eventually drive the other to extinction

similar species that have adjacent geographic ranges may be mutually restricting each other

this turns out to be very hjard to conclusively prove in practice

**on a graph, if they’re identical they would not overlap, if not identical, they overlap

connection to conservation

small geographic range size and/or small population size are the biggest risks for extinction

**if there’s a large area, if there’s a disturbance in one area, the species has a much higher chance of survival because they have more area to be in but if a species has a very limited geographic range, they can’t

is it range size or niche breadth that matters more for predicting the chance of going extinct?

geographic range size is the most important trait

why is it important to know any of this?

when species go extinct, we lose functional ecosystems

what happens when we lose functional ecosystems?

we lose ecosystem services:

• protection from flooding and fires

• plentiful supply of varied, good food

• medical discoviers

• beauty and inspiration