Chapter 19: Species Diversity in Communities Flashcards
Zoonotic Diseases
hosted by wildlife and are infectious to humans
Factors that affect emergence of zoonotic diseases
climate change, species invasions, pollution, and land use conversion
How does species diversity affect the emergence and transmission of zoonotic diseases?
declining species diversity facilitates emergence and transmission
Landscapes
made up of a patchwork of communities of different types
What does membership in a community depend on?
-regional species pools and dispersal ability
-environmental conditions
-species interactions
Regional Species Pool
provides an upper limit on the number and types of species that can be present in a community
Dispersal
supplies species to communities. The importance of dispersal can be seen in cases of non-native species invasions
How have humans expanded regional species pools?
by serving as vectors of dispersal
How do environmental conditions affect community membership?
a species may be able to get to a community but be unable to tolerate the environmental or abiotic conditions
How do species interactions affect community membership?
-coexistence with other species is also required for community membership
-other species may be required for growth, reproduction, or survival
-species may be excluded by competition, predation, parasitism, or disease
Biotic Resistance
occurs when interactions with the native species exclude the invader
-not a lot is known about biotic resistance
Climate change may facilitate species invasion by
- Altering pathways of transport and introduction
- Alteration of environmental constraints
- Alteration of the distributions of existing invasive species
- Impacts of non-native species may be altered
- Effects of management of non-native species
Resource partitioning
competing species are more likely to coexist if they use resources in different ways
Resource Spectrum
-each type of resource varies among a resource spectrum
-the resource use of each species falls somewhere along this spectrum and overlaps with the resource uses of other species to varying degrees
Read Slides 35-36
MacArthur (1958)
studied resource partitioning in a community of warblers in New England forests
-birds used different parts of the habitat different ways
MacArthur and MacArthur (1961)
looked at bird communities in 13 different habitats
-species diversity increased with foliage height diversity
-tree species identity was less important than structural complexity
Resource Ratio Hypothesis
species coexist by using resources in different proportions
Robertson et al. (1988)
mapped soil moisture and nitrogen concentration and found variation over small spatial scales
-this suggested resource partitioning In plants
What can modify species interactions and allow for species coexistence?
disturbance, stress, and predation
If the dominant competitor is prevented from reaching carrying capacity…
competitive exclusion cannot occur and coexistence will be maintained
Who was the first to consider disturbance as a mechanism to maintain species diversity?
Darwin
How did Darwin discover disturbance as a mechanism to maintain species diversity?
-in a meadow that he stopped mowing, he observes that the species number went from 20 down to 11
-without disturbance, the dominant species was able to exclude several others
Slides 49-51
Paine (1966)
studied competitive exclusion in the rocky intertidal zone
-When Pisaster was present, diversity was higher. Without it Mytilus outcompeted everything else
Intermediate disturbance hypothesis
-species diversity will be greatest at intermediate levels of disturbance
-at low levels of disturbance, competition regulates diversity. At high disturbance levels, many species cannot survive
Sousa (How does disturbance affect amount of species?)
studied communities on intertidal boulders that were overturned by waves
-small boulders (most overturned) had one species due to frequent disturbance
-most large boulders had two species (rare disturbance)
-intermediate sized boulders had four to seven species
Competitive Displacement
the best competition uses the limiting resources, reducing the weaker competitor’s population growth to the point of extinction
Dynamic Equilibrium Model
combines disturbance frequency and rate of competitive displacement to predict max species diversity at low, intermediate or equal levels
Slides 61-64
Menge and Sutherland Model (1987)
predation is a biological interaction and should be considered separately from disturbance
-predation is most important in low environmental stress
-as stress increases, predation importance decreases, and importance of competition increases
-at high stress levels, neither are important
Recruitment
influx of young individuals to a population
-if low, competition may not be important because resources are not limited
What do lottery models and neutral models emphasize?
the role of chance in maintaining species diversity
-all species have equal chances of obtaining resources made available by disturbances, and this allows coexistence
-species must have similar interaction strength and growth rates and be able to respond quickly to disturbances
Where is the lottery model most relevant?
very diverse communities where many species overlap in their resource requirements
What controls community functions such as disease suppression, plant productivity, water quality, etc.
species diversity
What valuable services do humans receive from community functions?
food and fuel production, water purification, oxygen and carbon monoxide exchange, flood protection
Diversity-Stability Theory
species richness is positively related to community stability
-tendancy of a community to remain the same in structure and function, or to return after a disturbance
Complementary Hypothesis
as species richness increases, community function will increase linearly
-each species has a unique and equally incremental effect
Redundancy Hypothesis
Functional contribution of additional species reaches a threshold
-as more species are added, there is overlap in their function, or redundancy among species
Idiosyncratic hypothesis
strength of ecological function varies greatly
-some species have a large effect, some have a minimal effect
-addition of dominant species will have a large effect on community function, producing a cure with a idiosyncratic shape
Case Study at end of powerpoint Slides 82-84
