Lecture 5: The ecological niche Flashcards
give a brief history of niche concept
> Grinell (1917)
- descriptive:
- lyrebird is a rainforest bird
Elton (1927)
- functional definition
- lyrebird: rainforest bird, omnivore, forages in leaf litter
niche is mode of life “in the sense that we speak of trades or jobs or professions in human community”
what is the modern concept of niche?
> hutchinson (1957)
- proposed to address interactions between tolerances and requirements to define conditions and resources needed by individual/ species
REFER TO DIAGRAMS
one dimension: temperature
two dimensions: temp and salinity
three dimensions
- more realistic, multidimensional niche
- e.g., temp, pH, food availability
dimensions = environmental factors that determine niche
what are the differences between a fundemental niche and a realised niche?
> if a location is characterised by conditions within limits for organism and provided it contains the required resources, then the species can potentially occur and persist.
this depends on :
1) species locating the site
2) presence of competitors and/or predators
Fundamental niche: describes overall potentialities of a species.
- i.e., niche of a species in the absence of competition from another species
Realised niche: more limited spectrum of conditions and resources that allow it to persist.
- i.e., niche of a species in the presence of competitors - precise nature depends on which competing species are present.
what is niche overlap?
> realised niche of one species may affect the realised niche of another is their fundamental niches overlap.
what is interspecific competition?
> lab experiment example
Asterionella and Synedra
both species can live alone in lab habitat
together = synedra excluded asterionella
synedra better exploiter of shared, limiting resource
Asterinella pop went extinct because Synedra used the resources to a level that could not be used by the Asterionella
Refer to diagram
describe the exmple of Salmonid Fish in Hokaido
> co-existence and exclusion of competing DVC and WSC
> decrease the size of eachothers fundamental niche to a realised niche
what are some general observations for realised niche according to competition?
1) competing species co-exist at one spatial scale but have distinct distributions at finer resolutions (fish in same stream but different altitudes)
2) inter specific competition can exclude species from locations where they can exist (DVC can live in WSC zone but only when WSC absent)
3) WSC zone part of fundamental niche of DVC but this zone is not a realised niche when WSC are present.
4) experimentation is important to understand systems
describe competition between non-related species
> competition may occur between:
- larger groups of species
- completely unrelated species of the same guild
EXAMPLE:
when feeding on the same resource:
- with ants removed: rodent population increased
- rodents removed: ant population increased
- each species alone consumed as many seeds as two specie together
- seeds built up in empty plots
- clear evidence for competition between the guild members
what is the competitive exclusion principle?
> if two competing species co-exist in a stable environment, then they do so as a result of niche differentiation (differentiation of their realised niche)
i.e., they are not using the limiting resources in the same way
if there is no differentiation, one species will eliminate the other
refer to the diagram
what is resource partitionin?
> species can co-exist if they use resources in different ways
BS1 and BS2 co-exist under white light: use different wavelength of light in photosynthesis
Co-existence of birds in the same habitat in british woodlands
all:
- short beaks
- hunt on twigs and leaves and on ground
- eat insects all year
- eat seeds in winter
- nest in tree holes
details of ecology
- precisely where within trees do they feed?
- size of insect prey
- hardness of seeds/size
do the 5 different species compete but co-exist by exploiting slightly different resources in slightly different ways?
this is difficult to prove and the natural environment is very complex
what is environmental heterogeneity
> interspecific competition proceeds not in isolation but in a patchy, impermanent and unpredictable environment
co-existence of a superior competitor and a superior coloniser
refer to diagram
because the system is so variable, once a spot because available, the algae jumps in, whereas the mussel is a better competitor.
what are aggregated distributions?
> aggregation ensures that most individuals compete with members of their own species
intraspecific aggregation negatively affected S.media but improved performance of other species.
what is a niche complementarity example?
> clown fish in PNG
different species with different anemones
same anemone, different clownfish depending on where it grows. inshore or offshore
refer to diagram
niche differentiation involves several niche dimensions: species of anemone, zone on shore, probably food particle size. Fish which are similar along one dimension tend to differ along another (e.g., large and small fish on one anemone)
the fish represent a guild. Intraspecific competition tends to shape communities by acting on guilds
