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Understanding Ecosystem Dynamics: Communities, Ecotones, and Biodiversity Patterns

This text explores the intricacies of ecological communities, defined as interacting populations in a shared habitat. It delves into ecosystem structure, including energy flow and biogeochemical cycling, as well as the significance of fixed species assemblages and the concept of ecotones—transitional zones between different communities. The study emphasizes key factors affecting biodiversity, such as species richness and diversity, along with the impact of edge effects on wildlife and vegetation. Additionally, insights into palynology reveal past plant communities through pollen analysis, enhancing our understanding of historical ecosystems.

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Understanding Ecosystem Dynamics: Communities, Ecotones, and Biodiversity Patterns

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  1. Communities An association of interacting populations in the same place at the same time -- have characteristic physiognomy Ecosystem A community plus its abiotic environment -- includes energy flow, biogeochemical cycling

  2. Communities as fixed species assemblages -- C. H. Merriam, 1890s Arizona -- all interacting species, co-dependent -- superorganism -- Life Zone concept

  3. Fig. 20.13 (EFB)

  4. Organismic or fixed concept Continuum concept Fig. 22.1 (EFB)

  5. Palynology: the study of pollen (fossil and recent) -- can identify grains to species by morphology -- preserve well in sediment cores from lakes, bogs -- represent past plant communities -- can radiocarbon date organic remains in cores to determine age of communities Margaret Davis: studied fossil pollen from lake cores in the eastern U.S.

  6. Ice sheet

  7. Fig. 21.26 (EFB)

  8. Community Structure Patterns visible in a community including: -- physiognomy -- dominant species -- number of trophic levels -- number and abundance of species species richness vs. species diversity

  9. Ecotones: intermixing of two communities where one transitions into another -- causes an ‘edge effect’ of greater species richness in the ecotone -- edges can be inherent or induced -- edges once thought to be good for wildlife management, but can be detrimental -- e.g., increased edge, more invasive species such as cowbirds entering forests

  10. Edge effects on forests • Changes in physical environment • e.g., temperature, humidity, light penetration • and wind 2. Direct biological changes e.g., dead trees and tree fall, reduced leaf fall, fewer forest birds 3. Higher order biological changes e.g., increase in some insect populations (butterflies and high light), increase in insectivores, more disturbances to interior

  11. Plant productivity and the number of bird species in temperate zone habitats Primary productivity No. of breeding Habitat (g/m2/yr) bird species Marsh 2000 6 Grassland 500 6 Shrubland 600 14 Desert 70 14 Coniferous forest 800 17 Upland deciduous forest 1000 21 Floodplain deciduous forest 2000 24

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