Niche Overlapping and Competition

B02602005 Tony Yen

Abstract• Terminology and Definition

• Determination of Niche

• Basic Concept of Niche Overlapping

• Relationship between Overlapping and Competition

• Case Study: Niche Variation Hypothesis

Terminology and Definition• The word “niche” derives from the Latin word

“nidus”, which means “nest”.• The ecological derivation of this word borrows

the concept from Hinduism.

Terminology and Definition

• Ecologists borrow such concept, and propose that each and every kind of species in an ecological system plays a special and exclusive role, since each species drill, prosper and reproduce only under a unique set of range of environmental variables.

Terminology and Definition

Terminology and Definition

Everyone has a unique role!!

• Definition:Following the concept above, we can define ecological niche as below:

Suppose in an ecological system there are n kinds of environment parameters (ex: temperature, solar insolation force etc.) of concern, say x1, x2, …, xn. For any particular species, it thrives only under certain ranges of these parameters, say

Then we call this specific set of range of parameters θ the niche of the particular species.

• This is known as the Hutchinsonian niche.

Terminology and Definition

Terminology and Definition

Determination of Niche

Spatial Distribution of a Population

Temperature

Precipitation

Determination of Niche

The niche of the population

Basic Concept of Niche Overlapping

• We know that every species has its unique range of food size preference. But other species might also have a range of preference which coincides with it at some value.

• The phenomenon is called niche overlapping.• Intuitively, if the niche overlapping of the two species

is greater, the interspecies competition of these two species increases. This is because of a more similar foraging pattern, causing the probability for two species to compete over the same food to increase.

Basic Concept of Niche

Overlapping

Basic Concept of Niche Overlapping

Basic Concept of Niche

Overlapping

Relationship between Overlapping and Competition

Competition Equation for Two Species

Non-Dimensionization

Overlapping& Competition

Reproduction Intra-species competition

Inter-species competition

Unstable Stable

Stable only if all eigenvalues are

negative!!

Relationship between Overlapping and Competition

• The inter-species competition coefficient b is governed by the niche overlapping of the two species.

• Suppose for each species the preference of the food size is a normal distribution and, just for simplification, having the same value of variation w and a spacing of mean d.

Overlapping& Competition

Relationship between Overlapping and Competition

• Then by clever reasoning we can figure out that the probability for two species to compete over the same resource would be

Overlapping& Competition

Don’t know why they dropped out the coefficient

Relationship between Overlapping and Competition

• In a stochastic environment where fluctuation is small, it can be shown that the minimum distance d has a constrain for which

• This is a very important result, because it will lead to the next important theory.

Overlapping& Competition

Case Study: Niche Variation Hypothesis

• If in the previous example we have n different species competing a limiting range (say L) of resource, we may obtain an approximated constrain on the “niche width” (evaluate by standard deviation w)

Niche Variation Hypothesis

Case Study: Niche Variation Hypothesis

• Which means that the more competitors, the less niche width a population should have.

• In 1965, Van Valen proposed the niche variation hypothesis.

• It claims that ‘‘populations with wider niches are more variable than populations with narrower niches’’

• Since then researchers have been continually testing the validity of this hypothesis.

Niche Variation Hypothesis

Case Study: Niche Variation Hypothesis

Research against NVH:In 2005 a team examined the skull and canine size of carnivore on islands and on continents. By NVH for the same species the size variation should be greater on islands, since less competitors implies wider niche.

Research pro NVH:In 2007 another team examined the variation of foraging food size of different types of animals; this research showed strong correlation between niche width and diet variation.

Hypothesis Rejected; team suggested that accessibility to

genetic interchange is more importantHypothesis Backed

Niche Variation Hypothesis

Case Study: Niche Variation Hypothesis

• The 2005 study disproves the connection between 1 and 3, while the 2007 study supports the connection between 2 and 3.

• So it may be the case where the mechanism is only “partially right”. That is to say, there might be many factors determining niche width, finding out the real mechanism from 1 to 2 may be a good research topic to do.

Less Competition Greater Niche Width Greater Variation

1 2 3

Niche Variation Hypothesis

What about time scale??

Thank you for your listening!!Reference:Mathematical Biology and Ecology, Dr. Ruth E. Baker, 2011, p.32-p.33

Niche Overlap as a Function of Environmental Variability, Robert M. May and Robert H. Mac Arthur, 1972

VARIABILITY AND SEXUAL SIZE DIMORPHISM IN CARNIVORES: TESTING THE NICHE VARIATION HYPOTHESIS, SHAI MEIRI et al. , 2005

Comparative support for the niche variation hypothesis that more generalized populations also are more heterogeneous, Daniel I. Bolnick et al. ,2007