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Chap.11 Community Structure
鄭先祐
生態主張者 Ayo工作室
Community Structure
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Equilibrium views
Predation as a structuring force
Non-equilibrium views
Tallgrass prairie, Bison, and Fire – A
synthesis
• Environmental Application (niche
specialization and extinction)
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Introduction
• Community
• Guild, a group of coexisting, ecologically
similar organisms.
• Adaptive radiation of Cichlid fish in Lake
Malawi, East Africa (Fig 11.1)
• Size relationships among granivorous
rodents in three desert communities in the
American Southwest (Fig. 11.2)
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Fig. 11.1 Adaptive radiation of Cichlid fish in Lake Malawi, East Africa
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Fig. 11.2
Size relationships
among granivorous
rodents in three desert
communities in the
American Southwest
niche 不重疊。
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Equilibrium views
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Inter-specific competition as a structuring
Changes in niche dimensions
Fundamental niche and realized niche.
Five similar species of warblers foraging in
the same tree (Fig. 11.3 and 11.4)
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Fig. 11.3 The five
species of warblers.
Note the similarity in
size and bill shape.
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Fig. 11.4 Feeding positions of five sympatric warblers.
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Fig. 11.4 Feeding positions of five
sympatric warblers.
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提高diversity的可能途徑
1. Increased niche overlap
2. Decreased niche breadth
3. Increased range of resources utilized.
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Niche specialization and extinction
• A highly specialized niche makes a species
vulnerable to competitive effects, particularly
from exotic species introduced into the habitat.
• The bird faunas of island systems like the
Hawaiian island exemplify this problem.
• Originally, the Hawaiian islands supported 84
species of endemic birds.其中以honeycreeper
species 演化最為radiation，有47種。其中有18
種已經在古老時代滅絕，另外8種於西方勢力
進入後就滅絕。剩下來的有20種是頻危的。
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圖11B-1. The diversity of honeycreeper species found on the Hawaiian
islands.
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Predation as a structuring force
• R. T. Paine (1966) studied the communities of
invertebrates and algae in the rocky intertidal zone
at Neah Bay, Washington (Fig. 11.7).
• This system is composed of a large group of
invertebrates and algae, with a single top carnivore,
the starfish, Pisaster ochraceous.
• 移走starfish 之後，種類從原本的15種，下降到
只有8 種。
• Keystone predator hypothesis.
範例
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Fig. 11.17 The rocky inter-tidal community.
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範例：Kangaroo rats in a desert
• 移走kangaroo rats ，經過12年。
• 植被有顯著的改變(圖11.18)。
• Annual and perennial grasses colonized and
increased three fold in the removal plots
(Fig. 11.9).
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圖11.18 圍牆的左邊是將kangaroo rats移走的地區。其植被明顯的
較多。
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圖11.19 Effects of
kangaroo rat (Dipodomys)
removal from enclosures.
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Non-equilibrium views
• In the past 20-years, ecologists have come to
suspect that most of the time, most populations
and communities are not at equilibrium.
• If change in the community is frequent and
devastating, process such as competition and
predation will be less important as determinants of
community structure.
• Disturbance and Patch dynamics models
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The Role of disturbance
• Abiotic factors such as fire, volcanic
eruptions, floods, and storms have different
impacts on the various species in a
community and thus affect community
organization.
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範例：bird community
• Wiens and Rotemberry (1980) study the bird
community structures in the Great Basin. 結果發
現於大區域是有consistent community
composition，但是於小區域，so much variation
among sites and among years within a site 因此無
法有固定的community composition。
• The severe and unpredictable climate
characteristic of the Great Basin prevents the
local species assemblages from achieving full
ecological saturation and resource limitation.
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Intermediate disturbance
• J. H. Connell (1979) introduced the
intermediate disturbance hypothesis to
explain the number of species coexisting in
a community. (Fig. 11.23)
• At low levels of disturbance, competition or
predation– processes Connell termed
“compensatory mechanisms” – reduces
species diversity.
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Fig. 11.23 Connell’s intermediate disturbance hypothesis. The
number of species in a community is maximal at intermediate levels
of disturbance.
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Patch dynamics models
The models emphasis the following properties
of communities:
• 1. Spatial variation in the nature of the
community.
• 2. Movement between patches via dispersal
of individuals.
• 3. Disturbance as an important feature of
communities.
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Three mechanisms
• 1. Functional relationships between species
counteract biologically induced instability.
• 2. Environmental disturbance decreases the
effect of biotic instability.
• 3. Species have compensatory mechanisms
that operate at low population densities to
prevent extinction.
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DeAgelis and Waterhouse (1987)
• 4. The isolation of subpopulations
determines the degree to which dispersal
can lead to repopulation of extinct patches.
• 5. Spatial hetrogeneity in physical and
biological factors leads to movement of
individuals to obtain important resources.
• (Fig. 11.24)
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範例：mussel community
• The structure os the community over time is
determined by the combined forces of
competitive interactions and physical
disturbance. (Fig. 11.25)
• Disturbance is sufficiently frequent that the
community is a mosaic of local sites, each
with a slightly different disturbance and
competitive history.
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範例：fossil mammal faunas
• Graham and colleagues (1996) analyzed
fossil mammal faunas from 2945 sites in the
US.
• The fossil record shows that most modern
communities emerged very recently.
• These data support the Gleasonian view of
communities as random, nonequilibrium
assemblages of species.
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Tall grass Prairie, Bison, and
Fire – A synthesis
• Deterministic biotic factors such as competition
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and predation
Stochastic influences such as disturbance
The tall grass prairie of North American occupied
some 68 million hectares before Europeans arrived.
C4 grasses, and C3 forbs, and with fire
Bison numbering between 30 and 60 million.
Fig.11.26, 11.27
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• 沒有食草地區，fire frequency 增加，導致C4
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grasses 增加覆蓋度。C3植物則減少。(Fig. 11.28)
火燒使得植被物種減少(Fig. 11.29)
The mechanism for this effect is shown in Figure
11.30.
Bison preferentially select burned areas because of
their preference for C4 grasses.
Grazing reduces the dominance of these species
and allows the C3 forbs to increase in numbers.
The largest numbers of species were found in plots
that were grazed or grazed and burned (Fig. 11.29).
Bison are considered to be keystone species in this
system.
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 問題與討論！
[email protected]
Ayo 文化站 http://faculty.pccu.edu.tw/~ayo
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