Ch20 Biodiversity.docx

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University of Toronto St. George
Spencer Barrett

BIO120H © Lis| Page 1011 chapter 20: BIODIVERSITY  why do so many org. live in the tropics? 1. diversity increases w/o limit over time  tropics are older, thus had time to accumulate more species  diversity is a matter of history 2. diversity reaches an equilibrium at which the appearance of new species balances the loss of already existing species  factors that add species weigh more heavily (and those that remove species less heavily) in the balance towards the tropics  but variation also occurs w/in latitudinal belts  suggests that a variety of processes influence the # of species somewhere  processes act uniform globe-wide  patterns in diversity that reflect the variations in temp. and precip. w/in a latitudinal belt imply the influence of local processes  geographic factors VARIATION IN THE RELATIVE ABUNDANCE OF SPECIES INFLUENCES CONCEPTS OF BIODIVERSITY  bbiodiversity variation among organisms and ecological systems at all levels, including genetic variation, morphological and functional variation, taxonomic uniqueness, and endemism, as well as variation in ecosystem structure and function  ecologists study most simple and general indices of biodiversity: species richness  measurement of the gravitas (“presence”) of a species depends on the purpose and method of study  rrelative abundance the proportional representation of a species in a sample or a community  quantified by the #, D, biomass of indiv. in a sample area, by the frequency of sample plots, or by cover (the proportion of the area of the habitat covered by a species)  rrank-abundance plot a graph that displays the abundances of species in a community or sample, usually on a logarithmic scale, ranked from the most common to the rarest  ddominant a species that is particularly abundant in or exerts great influence within an ecological system  heterogeneity measures: measures of species diversity  combine species richness w/ species evenness (variation in the abundances of species)  Simpson’s index DD): a measure of species diversity (heterogeneity measure) weighted by the relative abundance of each species THE NUMBER OF SPECIES INCREASES WITH THE AREA SAMPLED  OOlaf Arrhenius  species-area relationship: the positive relationship between species richness and the area of a habitat patch, island, or region  more indiv. are sampled  more habitat types included Species-area Relationships on Islands  on islands, species-area relationships are influenced by extinction (4 process)  endemic island species: a species found on that island and nowhere else  species richness increases w/ habitat diversity which increases w/ island size (and resulting topographic heterogeneity) BIO120H © Lis| Page 2011  larger islands are better targets for potential immigrants, and support larger pop.s which may persist longer owing to their genetic diversity LARGE-SCALE PATTERNS OF DIVERSITY REFLECT LATITUDE, ENVIRONMENTAL HETEROGENEITY, AND PRODUCTIVITY  increases from N to S  greater heterogeneity of envmt in Western US provides more suitable consitions for a greater # of species Ecological Heterogeneity and Habitat Productivity  more productive (complex) habitat = more species Solar Energy Input and Precipitation  Brad Hawkins et al.  solar NRG input influences species richness N of 15°  water availability had more influence on species richness in tropics through to SH  temp. relatively uniform in these areas  diff. in envmts mostly manifested through differences in precip.  potential evapotranspiration PETT): the amount of water that could be transpired by plants and evaporated from the soil, given the local temperature and humidity, if water were not limited  describes the input of NRG into a system  energy-diversity hypothesis: there is a causal relationship b/w PET and species richness  more NRG can be shared by more species DIVERSITY HAS BOTH REGIONAL AND LOCAL COMPONENTS  local diversity: a.k.a. alpha diversity; the number of species in a small area of homogeneous habitat  regional diversity: a.k.a. Gamma diversity; the number of species observed in all habitats within a large geographic area that includes no significant barriers to dispersal  beta diversity: the difference, or turnover, in species from one habitat to another Local Communities and the Regional Species Pool  species pool: the entire group of species within a source region from which colonists of an island or habitat patch are drawn  species sorting: a process that determines membership in a local community based on the tolerances of species from the regional species pool for local conditions, their requirements for resources, or their interactions with competitors, predators, and pathogens  sowed seeds of 20 species in 120 wetland microcosms (differed in soil fertility, water depth, fluctuation in water depth, soil Evan Weiher texture, organic leaf litter) Paul Keddy  # of species in each community decreased (due to competition) (species sorting  diversity fell from 15 species to 3-5 species depending on soil fiin wetland plant fertility communities)  species composition differed since communities developed under ecologists in the diff. envmts  thus, envmtal filters contribute to species sorting BIO120H © Lis| Page 3011 Species Interactions and Ecological Release  competition has a major role in species sorting  more species = more species sorting  thus, each species should be able to maintain itself over only a narrow range of most adapted habitats  beta diversity should be high  ecological release: expansion of habitat and resource use and increase in abundance by ecological release a population in a region of low species richness  ex. island species (occur in greater D and expand into habitats that would be filled by other species on the mainland)  islands w/ fewer species, species occur in higher abundance and live in more habitats (broader realized niche) DIVERSITY CAN BE UNDERSTOOD IN TERMS OF NICHE RELATIONSHIPS  fundamental niche represents the range of envmtal conditions, habitat structures, and resource qualities w/in which an indiv. or species can survive and reproduce  niche overlap depends on the level of competition b/w species  community has a total niche space w/in which its member species must fit  communities w/ diff. species #’s differ in: total community niche space, niche overlap among species, niche breadth (degree of specialization) of indiv. species  species can be added by increasing niche overlap (sharing of niche space) or decreasing niche breadth (partitioning total niche space more finely) Competition, Diversity, and the Niche  higher diversity = weaker competition  more diversity in tropics  greater variety of resources  bird, bat, and insect species are numerous in the tropics due to the many species of suitable resources they have  nonflying mammals are no more diverse at equator than in temperate regions Species Diversity and Niche Diversity  niche diversity assessed using morphology as an indicator of ecological role  increase in species diversity = increase in niche diversity  more diverse communities have a greater variety of ecological resources (more niche space)  bats in Canada  small insectivores  less diverse community w/ similar morphology  bats in West Africa  diverse  exploit a far greater vari
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