Read the summary and the most important questions on Leereenheid 4 - Interspecifieke concurrentie en soortenrijkdom

• 6 Interspecific competition

• 6.2.3 Some general observations

• What are the 4 general points regarding interspecific competition?

  1. Competing species often coexist at one spatial scale, but have more distinct distributions when you look more closely. 
  2. Species are often excluded by interspecific competition from locations at which they could exist perfectly well in the absence of interspecific competition. 
  3. Fundamental niche vs realized niche.
  4. Competing species can coexist when both are provided with a realized niche by their habitat, but even in a realized niche a species may be excluded by another species that denies its realized niche here.

• 6.2.7 The competitive exclusion principle

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• What does the competitive exclusion principle not say?

  • That whenever we see coexisting species with different niches it is reasonable to jump to the conclusion that this is the principle in operation. 
    
  • Each species has their own niche and this does not prove that there are coexisting competitors.  
    

• What will coexisting species with the potential to compete do?

  They will exhibit differences in behavior, physiology or morphology that ensure that they compete little or not at all. = character displacement.

• 10 Patterns in species richness

• 10.1 Introduction

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• Why is it difficult to count or list the number of species in a community?

  Because of taxonomic inadequacies and because only a portion of the organisms in an area can usually be counted.

• What do diversity indices describe?

  They are designed to combine both species richness and the evenness or equitability of the distribution of individuals among those species.

• 10.2 A simple model of species richness

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• What is the niche breadth (n)?

  • The portion of the resource continuum (R) that each species uses. 
  • Average niche breadth is ñ.
    

• Explain why some communities can/should contain more species than others using niche breadth, and overlap.

  1. For given values of ñ and õ, a community will contain more species the larger the value of R (=greater range of resources). 
  2. For a given R, more species will be accommodated if ñ is smaller (=species are more specialized in their use of resources)
  3. With a greater õ, more species will coexist along the same R.
  4. A community will contain more species the more fully saturated it is. It will contain fewer species when more of the R is unexploited. 

• When are resources likely to be fully exploited? On what will species richness then be dependent?

  • When a community is dominated by interspecific competition. 
    
  • Species richness will then depend on the range of available resources, the extent to which species are specialists and the permitted extent of niche overlap. 

• What is the effect of predation on species richness?

  • Predators can exclude certain prey species, which might lead some resources to be unexploited (fig d) and species richness may be reduced. 
  • Predation may keep species under their carrying capacity, reducing the intensity and importance of direct interspecific competition for resources. This permits more niche overlap and greater species richness than in a community dominated by competition (fig. c)

• 10.3.1 Productivity and resource richness

• What is the relation between productivity of the environment and species richness?

  Increased productivity of the environment might be expected to lead to increased species richness.