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Ecology 2483 > Lecture 17 > Flashcards

Lecture 17 Flashcards

1
Q

Distribution and Abundance of Species in Communities Depends on:

A
  1. Regional species pools and dispersal ability
  2. Abiotic conditions
  3. Species interactions
    - These factors act as “filters” which exclude species from (or include species in) particular communities
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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
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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
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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
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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
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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
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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
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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
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9
Q

Diatom Species Coexist in Nature

A
  • To explain this Tilman proposed the resource ratio hypothesis
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10
Q

Resource Ratio Hypothesis

A
  • pecies coexist by using resources in different proportions
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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
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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
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13
Q

Intermediate Disturbance Hypothesis

A
  • Species diversity should be greeted at intermediate disturbance
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14
Q

At Low Disturbance

A
  • competition determines the diversity
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15
Q

At High Disturbance

A
  • many species cannot survive
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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
Q

Diversity-Stability Theory

A
  • 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
Q

Three Hypotheses Have Been Proposed To ___

A
  • explain the positive relationship between species diversity and community function
27
Q

2 Variables in all the Hypotheses

A
  • Degree of overlap in ecological function of species
  • Variation in the strength of the ecological functions of species
28
Q

Complementarity Hypothesis

A
  • As species richness increases, there will be a linear increase in community function
  • Each species added has an equal effect
29
Q

Redundancy Hypothesis

A
  • 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
Q

Idiosyncratic Hypothesis

A
  • Dominant species have a much larger effect on community function than other species

Ecology 2483 (21 decks)

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