Ch18 Community Structure.docx

5 Pages
74 Views
Unlock Document

Department
Biology
Course
BIO120H1
Professor
Spencer Barrett
Semester
Fall

Description
BIO120H © Li| Page 12011 chapter 18: COMMUNITY STRUCTURE  Frederic E. Clements  communities are superorganisms  the functions of various species are connected and have evolved to enhance their interdependence  communities are discrete entities that can be distinguished from one another  it is aholistic conceptt (the idea that the organisms in a community form a discrete, complex unit analogous to a superorganism)  Henry A. Gleason  advocated an inindividualistic conceptf community organization (the idea that a community is not a discrete unit, but merely a fortuitous association of species whose adaptations and requirements enable them to live together under the physical and biological conditions of a particular place)  natural selection acts on the fitness of the indiv. to maximize its own reproductive success, not the benefit the community  community: an association of interacting pop. usu. defined by the nature of their interaction or the place in which they live A BIOLOGICAL COMMUNITY IS AN ASSOCIATION OF INTERACTING POPULATIONS  a community can be spatially defined, including all the pop. w/in its boundaries  Braun-Blanquet sys.: a taxonomy of communities based on a method of sampling plant species composition  places each community in a hierarchy of types when organized by their similarity  closed community: a community in which the distributions of several species coincide closely, but are largely separated from those of other sets of species  consistent w/ holistic view  species closely related, and share ecological tolerance limites  ecotone: a region of rapid turnover of species along a spatial transect or ecological gradient; a zone of transition b/w communities (boundaries of closed comm.)  open community: a local association of species having independent and only partially overlapping ecological distributions  no natural boundaries Ecotones  where species reach the edges of their distributions  prominent at sharp community boundaries ex. terrestrial & aquatic, diff.-facing slopes  some plants only grow in ecotones, or on either sides of ecotones, and others are not affected by the differing conditions around the ecotones  dominant plants can create ecotones by competition AND through altering the envmt  ex. sharp boundary b/w broad- and coniferous- leaved forests  decomposition of conifer needles makes soil acidic, resulting in diff. soil conditions  diff. distributions of herbs and shrubs  ex. fire maintains ecotones b/w prairies and forests  perennial prairie grasses resist fire that kills tree seedlings, but fire can’t penetrate deeply into moist forest BIO120H © Lis| Page 2011 The Continuum Concept and Gradient Analysis  continuum: a gradient of envmtal characteristics or of change in the composition of communities  gradient analysis: the plotting and interpretation of the abundance of species along an gradient analysis envmtal gradient  gradient: ex. moisture, temp., salinity, exposure, light level  Robert Whittaker  puts to rest Clements’ view of extreme closed communities  Whittaker found that dominant trees in the Great Smoky Mountains of Tennessee have distinct but partially overlapping ecological distributions on a gradient MEASURES OF COMMUNITY STRUCTURE INCLUDE NUMBERS OF SPECIES AND TROPHIC LEVELS  species richness: a simple count of the number of species in an area  more species live in tropical regions than temperate and boreal  one way to partition species is according to their feeding relationships  trophic levels: a position in a food web, determined by the number of energy transfer steps from primary producers to that level  autotrophic: an organism that assimilates energy either from sunlight or from inorganic autotrophic compounds  primary producer: a plant or other autotroph that assimilates the energy of sunlight (a photoautotroph) or reduced inorganic compounds (a chemoautotroph) and uses it to synthesize organic compounds  primary consumer: an herbivore; an organism at the lowest consumer level in a food web  secondary consumer: a carnivore; a consumer of primary consumers  guild: a group of species that occupy similar ecological positions within the same community  grouped together within trophic levels by types of resources consumed, and methods or locations of foraging FEEDING RELATIONSHIPS ORGANIZE COMMUNITIES IN FOOD WEBS  food web: a representation of the various interconnected paths of energy flow through populations in a community, taking into account the fact that each population shares resources and consumers with other populations Effects of Species Richness on Food Web Structure  omnivory: feeding on more than one trophic level  complexity of a food web is based on the # of feeding links and trophic levels  # of trophic levels (and guilds) increases w/ species richness  increasing species richness is associated w/ increasing food web complexity  # of feeding links per species is independent of the species richness of the community BIO120H © Lis| Page 3011 Effect of Food Web Structure on Species Diversity  species diversity increases food web diversity  feeding relationships affect species diversity w/in a community  John Terborgh et al. (consumer effect on species diversity) John Terborgh  unintended predator removal in rain forests of Venezuela by dam  dam created patches – too small to support predators of the herbivores  howler monkeys, green iguanas –pop. skyrocketed  ecosystem “meltdown” occurred and affected regeneration of trees and decreased productivity and plant diversity  keystone consumer: species, often a predator, that has a dominant influence on the structure of a community, which may be revealed when that species is removed A Variety of Food Web Types  Robert Paine  described diff. types of food webs that describe diff. ways in which species influence one another w/in communities  connectedness web: a food web that emphasizes the feeding relationships among species
More Less

Related notes for BIO120H1

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit