Niches Flashcards
Lecture 10
What is a niche?
The position in life
to which the holder
is well suited
What is a fundemental niche?
Interspecific competition influences the
niche of a species
the full range of conditions and resources under which a species can survive and reproduce.
What is the realised niche?
Interspecific competition influences the
niche of a species
.the portion of the fundamental niche that the species actually exploits.
What is niche overlpa?
When two or more organisms use a portion of the same resource (food or
habitat) simultaneously
– Depends on the degree of competition for that resource
▪ Extensive niche overlap may indicate that little
competition exists and that resources are abundant.
How does Interspecific competition influences the
niche of a species?
Looking at Stipa neomexicana
– S. neomexicana grows mainly on dry ridges, not in
moister conditions lower on mountain slopes
Interspecific competition influences the niche of a species
– Neighbouring plants were
removed from experimental blocks in mid-slope and low-lying areas
▪ Growth, survival & reproduction compared to control plants (neighbours not removed)
– When neighbors are removed,
– Stipadistribution is limited to Ridge crest is sub-optimal but it is forced to grow there because there are more competitors on the lower and mid slope.
What is competitive release?
Expansion of a niche
after the removal of a competitor OR when a
species invades an island and expands into
unoccupied habitats
– Cattail (Typha ) distribution
– Baleen whales that feed on Krill - increase in other krill-dependant predators [seal and penguins]
How does coexistence of species often involve
partitioning available resources?
▪ Many species can have identical resource requirements and occupy very similar niches - 1 will eventually outcompete the other.
▪ Coexistence of competitors is associated with niche differentiation.
▪ Niche differentiation may result from sharing
available resources (resource partitioning).
How does competition influence natural selection?
▪ Resource partitioning results from specific
physiological, morphological or behavioural adaptations that allows species to utilize different resources or survive under different conditions:
– outcome of interspecific competition in the past
▪ Differences among species living today have
evolved over a long time, but we don’t know what resources and potential competitors may have influenced natural selection
– “ghosts of competition past”
What is character displacement?
shift in feeding niche that
subsequently affects
morphology, behaviour, or
physiology
Example with bird species.
▪ P. Grant and R. Grant (Princeton University) studied medium and small ground finches that feed on an overlapping range of seed sizes.
Both bird species live on
the same island - no over lap in beak depth.
Only one bird species per island - more over lap in beak depth.
An Animal’s Habitat Reflects a Wide Variety of Adaptations to the Environment
▪ Each species occupies a specific Habitat
▪ Depends on ability of the environment to
provide essential resources and conditions
necessary for survival, growth and reproduction
▪ Habitat reflects diverse adaptations relating to
feeding, mating & reproductive behaviours &
needs.
How do sessile organisms chose a habitat?
-Passive dispersal & selection
-Luck of the draw - die if habitat is unsuitable.
▪ Settlement cues - presence of conspecific adults, presence of suitable food. (detect cues if the environment is suitable).
How do mobile animals chose a habitat?
- Active habitat selection
▪ Habitat selection in birds
-structural features of the vegetation
-Vertical layers particularly important - shurbs, small trees, tall canopy. [nesting, food sites]
How to garter snakes and aphids choose their environment?
▪ Garter snakes choose rocks according to thickness
▪ Intermediate thickness rocks just right
▪ Aphids that parasitize cottonwoods prefer larger
leaves and select specific positions -
