Lecture 17 Flashcards
1
Q
Distribution and Abundance of Species in Communities Depends on:
A
- Regional species pools and dispersal ability
- Abiotic conditions
- Species interactions
- These factors act as “filters” which exclude species from (or include species in) particular communities
2
Q
Regional Species Pools and Dispersal Ability
A
- Regional species pool provides an upper limit on the number and types of species present in a community
- Importance of dispersal can be seen in cases of non-native species invasions
- Humans have greatly expanded regional species pools by serving as vectors of dispersal
Ex; aquatic species travel around the world in ballast water carried by ships
3
Q
Abiotic Conditions
A
- A species may be able to get to a community but be unable to tolerate the abiotic conditions
Ex. a lake might not support organisms that require fast-flowing water - Many species that are dispersed in ballast water can’t survive in a new habitat because of temperature, salinity, etc
- We can’t rely on physiological constraints to exclude invaders
4
Q
Species Interactions
A
- Coexistence with other species is also required for community membership
- Other species may be required for growth, reproduction, or survival
- Species may be excluded from a community by competition, predation, parasitism or disease
5
Q
Biotic Resistance
A
- occurs when interactions with the native species exclude the invader
Ex. native herbivores can reduce the spread of non-native plants - Not much is known about biotic resistance
because failed introductions of non-native species tend to go undetected
6
Q
Resource Partitioning
A
- competing species coexist by using resources in different ways. It reduces competition and increases species richness
- In a simple model, each species’ resource use falls on a spectrum of available resource
- more overlap: more competition between species
- less overlap: more specialized species have become and the less strongly they compete
7
Q
MacArthur
A
- 1958
- Studied resource partitioning in a community of warblers in New England forests
- Recorded feeding habits, nesting locations, and breeding territories
8
Q
When MacArthur mapped the locations of warbler activity
A
- he found that the birds were using different parts of the habitat in different ways
9
Q
Diatom Species Coexist in Nature
A
- To explain this Tilman proposed the resource ratio hypothesis
10
Q
Resource Ratio Hypothesis
A
- pecies coexist by using resources in different proportions
11
Q
Tilman’s Experiment
A
- Two diatom species were grown in media with different SiO2 : PO4 ratios
- Cyclotella dominated only when the ratio was low (asterionella cant dominate because there are not enough cilia)
- Asterionella dominated when the ratio was high
- Coexistence occurred only when SiO2 and PO4 were limiting to both species
12
Q
Proccesses that Promote Coexistence
A
- Disturbance, stress, predation, and positive interactions can mediate resource availability, thus promoting species coexistence and species diversity
- When the dominant competitor is unable to reach its own carrying capacity: competitive exclusion can’t occur, and coexistence will be maintained
13
Q
Intermediate Disturbance Hypothesis
A
- Species diversity should be greeted at intermediate disturbance
14
Q
At Low Disturbance
A
- competition determines the diversity
15
Q
At High Disturbance
A
- many species cannot survive
16
Q
Sousa
A
- Studied communities on intertidal boulders in southern California that were overturned by waves
- Small boulders were overturned frequently (disturbance)
- Large boulders were overturned less often
- The high and low disturbance is relative
- High diversity: well-balanced
17
Q
Potential Role of Positive Interactions
A
- New England salt marsh, 3 intertidal zones were identified with different species composition
- Middle intertidal zone had the greatest species richness
- Low zone physiology stress (frequent inundation) was the main controlling factor
- Concluded that positive interactions were critically important in maintaining species diversity, especially at intermediate stress levels
18
Q
Menege-Sutherland Model
A
- Separates the effects of predation from those of disturbance and stress
- The above theories assume an underlying competitive hierarchy
19
Q
Lottery Models
A
- Emphasize the role of chance in maintaining species diversity
- All species have equal chances of obtaining resources that were made available by disturbances (Which allows coexistence)
20
Q
Species Must Have
A
- similar interaction strengths
- similar growth rates
- the ability to respond quickly to disturbances that free up resources
21
Q
Sale (1977)
A
- Looked at patterns of occupation of new sites by three fish species, and found it to be random
- The lottery model may be most relevant in very diverse communities but decreases in communities which species have large disparities in interaction strength
22
Q
One Important Component of this System
A
- Fishes produce many mobile juveniles that can saturate a reef and quickly take advantage of open space
23
Q
The Consequences of Diversity
A
- The central idea in ecology is: that species diversity can control community functions, such as plant productivity, soil fertility, water quality, etc
24
Q
Many Community Functions also Provide Valuable Services to Humans
A
- Food and fuel production
- Water purification
- O2 and CO2 exchange
- Protection from catastrophic events, such as floods
25
Diversity-Stability Theory
- Long-standing idea that species richness is positively related to community stability
- Tendency of a community to remain the same in structure and function
26
Three Hypotheses Have Been Proposed To ___
- explain the positive relationship between species diversity and community function
27
2 Variables in all the Hypotheses
- Degree of overlap in ecological function of species
- Variation in the strength of the ecological functions of species
28
Complementarity Hypothesis
- As species richness increases, there will be a linear increase in community function
- Each species added has an equal effect
29
Redundancy Hypothesis
- the functional contribution of additional species reaches a threshold
- As more species are added, there is overlap in their function or redundancy among species
30
Idiosyncratic Hypothesis
- Dominant species have a much larger effect on community function than other species
