Lecture 6 - Competition Flashcards
Describe Grinnell’s Niche.
Grinnell 1917
Species are expected to occupy the geographical region matching their environmental tolerances.
The Grinnelian niche concept embodies the idea that the niche of a species is determined by the habitat in which is lives in.
It is a distributional unit within each species held by its structural and functional limitations (habitat).
What is the definition of a niche?
The functional role of an organism in its environment.
What is Hutchinson’s niche?
The Hutchinson niche is the modern concept of a niche and consists of many physical and environmental variables existing in a multi dimensional space.
It is an n-dimensional hyper volume, where the dimensions are environmental conditions and resources. The hyper volume defines the multi-dimensional space that resources such as light, nutrients and structure are available to organisms.
How did Elton describe a niche?
‘A fundamental role of an organism in the community,
what it does and its relationship to food.’
What evidence is there fore Grinnell’s niche?
Thistles have lower reproductive output (seeds per head) further north.
Experimental evidence:
Shading lowers temperature & no. of seeds
Spraying has the same effect (evaporation)
Distribution limit determined by the conditions under which the population cannot replace itself
What is Elton’s niche?
Elton’s niche means its place in the biotic environment, its relation to food and enemies.
What is the fundamental niche?
The fundamental niche is the modern view of a niche, (Hutchinson’s niche). It is where an organism would live in the absence of other species
What is the realised niche?
The realised niche is the realistic niche that is seen in nature as the fundamental niche is almost never observed.
Other species lead to OVERLAP in resource requirements.
The realised niche is what is left over after interactions with other species in the habitat have occurred?
What is Gause’s principle?
Gause’s principle is competitive exclusion
No two species occupying the same niche can exist indefinitely, through competition one will force the other to become extinct or shift in behaviour to occupy a new niche. This occurs when one species has just the slightest advantage over the other.
‘Complete competitors cannot coexist’
What patterns of resource use does Hutchinson’s niche describe?
Resources are partitioned to minimise overlap and competitive exclusion as too great similarity results in this. Niches have regular spacing, they are dispersed, the fundamental niche becomes the realised niche in the presence of predators.
What patterns of resource use does Grinnell’s niche describe?
Resource use is determined mainly by habitat choice, foraging method, the environment etc. Niches are not over dispersed.
What is a vacant niche?
The concept that more species could exist than are present at a particular time due to unoccupied niches being present.
They do not exist for Hutchinson’s niche but could be present for Grinnell’s niche.
Describe the World is Green theory.
HSS
The World is Green
food quality matters only for herbivores, predicts competition between plants and predators, not herbivores
Herbivore populations are kept below K by natural enemies.
Escape from predation should be the major force that shapes niches
What is the inadequate environment hypothesis?
Food shortage governs all trophic levels, mainly N
Food suitability varies
Limiting resources sometimes leads to competition
In a hostile environment you survive by chance
Predators affect prey only when increase and disperse more rapidly than prey
Poor conditions prevent predators from using all available food
What are the mechanisms for competition?
Consumptive Pre-emptive Overgrowth Chemical Territorial Encounter
