Chap.11 Community Structure

Chap.11 Community Structure

鄭先祐

生態主張者 Ayo 工作室

2001 chap.11 Com生態學munity structure

2

Community Structure

• Equilibrium views

• Predation as a structuring force

• Non-equilibrium views

• Tallgrass prairie, Bison, and Fire – A synthesis

• Environmental Application (niche specialization and extinction)


3

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)


4

Fig. 11.1 Adaptive radiation of Cichlid fish in Lake Malawi, East Africa


5

Fig. 11.2Size relationships

among granivorous rodents in three desert

communities in the American Southwest

niche 不重疊。


6

Equilibrium views

• 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)


7

Fig. 11.3 The five species of warblers. Note the similarity in size and bill shape.


8

Fig. 11.4 Feeding positions of five sympatric warblers.


9

Fig. 11.4 Feeding positions of five sympatric warblers.


10

提高 diversity 的可能途徑

1. Increased niche overlap

2. Decreased niche breadth

3. Increased range of resources utilized.


11


12

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。


13

圖 11B-1. The diversity of honeycreeper species found on the Hawaiian islands.


14

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


15Fig. 11.17 The rocky inter-tidal community.


16

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).


17

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。


18

圖 11.19 Effects of kangaroo rat (Dipodomys) removal from enclosures.


19

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


20

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.


21

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.


22

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.


23

Fig. 11.23 Connell’s intermediate disturbance hypothesis. The number of species in a community is maximal at intermediate levels

of disturbance.


24

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.


25

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.


26

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)


27


28

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.


29


30

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.


31

Tall grass Prairie, Bison, and Fire – A synthesis

• Deterministic biotic factors such as competition 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


32


33


34

• 沒有食草地區， fire frequency 增加，導致 C4 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.


35


36


37


38

問題與討論！

[email protected]

Ayo 文化站 http://faculty.pccu.edu.tw/~ayo

Documents

Chap.11 Community Structure