Chap. 9 from populations to communities 鄭先祐 (Ayo) 國立臺南大學 環境與生態學院 生物科技學系 生態學 (2008) Essentials of Ecology 3 rd. Ed.

2 From populations to communities 9.1 introduction 9.2 multiple determinants of the dynamics of populations 9.3 dispersal, patches and metapopulation dynamics 9.4 temporal patterns in community composition ( 群落組成 ) 9.5 food webs ( 食物網 )

3 9.1 introduction Fig. 9.1 community matrix illustrating how each species may interact with several others in competitive interactions, or between grazers, or between predators and predator-prey interactions.

4 9.2 multiple determinants of the dynamics of populations Fig. 9.2 correlation between population growth rate and food availability (a) red kangaroo (b) Barn owl

5 Fig. 9.2 correlation between population growth rate and food availability (c) wildebeest (d) feral pig

6 9.2 fluctuation or stability? Fig. 9.3 (a) the population dynamics of Androsace septentrionalis during an 8-year study.

7 Fig. 9.3 (b) irregular irruptions in the abundance of house mice in an agricultural habitat in Victoria, Australia,

determination and regulation of abundance Abundance is determined, or regulated? –Regulated, density-dependent factors –Determined, density-independent factors Fig. 9.4 (a) population regulation with (i) density-independent birth and density-dependent death

9 Fig. 9.4 (b) population regulation with density-dependent birth, b and density- independent death, d.

10 Fig. 9.5 idealized diagrams of population dynamics: (a) dynamics dominated by phases of population growth after disasters (b) by limitations on environmental carrying capacity, where the carrying capacity is high.

11 (c) same as (b) but where the capacity is low (d) dynamics within a habitable site dominated by population decay after more or less sudden episodes of colonization or recruitment.

key factor analysis K- value, killing power value

key factor analysis

14 Fig. 9.6 (a) density-dependent emigration by Colorado beetle summer adults (b) density-dependent starvation of larvae.

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16 Fig. 9.7 key factor analysis of the sand-dune annual plant.

dispersal, patches and metapopulation dynamics The theory of island biogeography, MacArthur and Wilson (1967) Metapopulation dynamics, Levins (1969) 1.The dynamics of individuals within patches 2.The dynamics of the occupied patches themselves within the overall metapopulation –The whole idea of metapopulation was largely neglected during the 20 years after Levin’s initial work. –The 1990s, however, saw a great flowering of interest.

18 Fig. 9.9 the metapopulati on dynamics of the American pika in Bodie, California (a) the relative positions and approximate sizes.

19 Fig two metapopulations of the silver- studded blue butterfly in North Wales. (a) in a limestone habitat, where there was large number of persistent ( 長久的 ) local populations among smaller, much more ephemeral ( 短暫的 ) local populations

20 (b) in a heath land habitat, where the proportion of smaller and ephemeral population was much greater.

temporal patterns in community composition ( 群落組成 ) founder-and dominance-controlled Community succession 9.4 Topical ECOncerns: conservation sometimes requires manipulation of a succession –A giant New Zealand insect, the weta Deinacrida mahoenuiensis (Orthoptera)( 直翅目 ).

Founder-controlled and dominance- controlled communities Founder controlled: when all species are good colonists and essentially equal competitors –Communities of tropical reef fish (Table 9.4) Dominance controlled, when some species are strongly superior competitively –Fig (hypothetical succession)

23 Founder-controlled communities

24 Fig Hypothetical succession in a gap.

community succession Primary succession Secondary succession Fig seedling emergence from added seeds of species typical of different successional stages on dunes of four ages.

26 Fig variation in the relative importance of six species during an old-field succession on the Loess Plateau in China.

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28 Add. Table 9-1

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30 Fig Comparison of the energetics of ecosystem development in (A) forests.

31 Fig Comparison of the energetics of ecosystem development in (B) microcosms.

food webs indirect and direct effects –Fig. 9.17, a simple model –Trophic cascade (indirect effect) population and community stability and food web structure –Keystones species

33 Fig 三者間關係。 若有三者，則可共存。 倘若缺少 superpredator ， prey 會 extinction.

34 Fig when birds are excluded from the intertidal community, barnacles increase in abundance at the expense of mussels ( 貽貝 ), and three limpet ( 帽貝 ) species show marked changes in density.

35 Top-down control? Bottom-up control? Why is the world greens? –Because top-down control predominates: green plant biomass accumulates because predators keep herbivores in check. –Or the world is prickly ( 多刺的 ) and tastes bad (Pimm, 1991)

36 Fig top-down control, but only with low productivity. (a) snail biomass (b) plant biomass

37 Fig top-down control, but only with low productivity. (a) snail biomass (b) plant biomass

stability and food web structure Keystone species, the removal of some strong interactors leads to significant changes spreading throughout the food web, we refer to these as keystone species. The characteristics of food web –Numbers of species they contain –The connectance of the web –The average interaction strength between pairs of species

39 Add Fig. 9-2 typical food web for a terrestrial ecosystem.

40 Fig The relationships between connectance and species richness. (a) a compilation from the literature of 40 food webs from terrestrial, freshwater and marine environments. (b) a compilation of 95 insect-dominated webs from various habitats.

41 Fig The relationships between connectance and species richness. (c) seasonal versions of a food web for a large pond in northern England, varying in species richness from 12 to 32. (d) food webs from swamps and streams in Costa Rica and Venezuela.

42 Review questions 1.What is meant by a ‘metapopulation’ and how does it differ from a simple ‘population’? 2.What are meant by bottom-up and top- down control? How is the importance of each likely to vary with the number of trophic levels in a community?

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