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Community Ecology BSC 405

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Title: Community Ecology BSC 405


1
Community Ecology BSC 405
  • Fall 2010
  • Steven Juliano

2
Access to course materials
  • Assigned readings Either
  • email of pdf
  • or photocopy
  • Lecture notes Power points
  • Posted on my web page
  • Emailed to you
  • You print

3
What is Community ecology?
  • One level in the hierarchical levels of
    organization in Ecology.
  • Ecology -- The science of how organisms interact
    with their living and non-living environment
  • Ecology -- The distribution and abundance of
    organisms

4
Hierarchy
  • Individuals
  • Populations
  • Communities
  • Ecosystems

5
Individuals
  • Physiology
  • Behavior
  • Reproductive schedules
  • Homeostasis
  • Adaptation, evolutionary ecology

6
Populations
  • Dynamics
  • Regulation
  • Age structure
  • Spatial structure, metapopulations
  • Sex ratio, Mating system

7
Communities
  • Properties patterns
  • Number of species
  • Relative abundances
  • Morphology
  • Trophic links
  • Succession
  • Processes
  • Disturbances
  • Trophic interactions
  • Competition
  • Mutualism
  • Indirect effects

8
Ecosystems
  • Energy flow
  • Cycles of matter
  • Global change, climate

9
Definitions / Jargon (see also Morin, chapter 1)
  • Community Organisms living in one place, at one
    time, and actually or potentially interacting
  • Metacommunity set of local communities that are
    linked by dispersal of multiple potentially
    interacting species
  • Taxocene Organisms of a particular taxon
    occurring together in one place (e.g., plant
    community)
  • Component community species occupying, e.g.,
    one plant species, and drawing part of their
    resource needs from that plant

10
Time scale of study
  • Ecological
  • How a community functions now
  • How do contemporary processes act to maintain
    observed community structure?
  • Evolutionary
  • History of how a community came to its present
    state over evolutionary time
  • How do species evolve in response to selection
    due to community processes?

11
Ecological vs. Evolutionary questions
  • Ecological studies much more readily done
  • Evolutionary studies rely less on direct
    experiment and more on comparative,
    observational, theoretical methods
  • Evolutionary questions imply ecological questions
  • Ecological questions do not necessarily imply
    evolutionary questions

12
Investigating communities
  • Investigation and description of community
    pattern
  • Any study of interacting species is a community
    level study
  • Investigations of the processes that determine
    community properties

13
Community processes causes of patterns
  • Tolerances to the physical environment and
    disturbance
  • Species interactions population / individual
    effects

14
Community processes causes of patterns
  • Spatial or landscape effects
  • proximity effects patterns in a community
    depend on proximity of that community to others
  • metacommunities
  • Regional processes
  • community pattern is driven not by local
    processes (competition, tolerance, etc.) but
    regional floristic/faunistic effects

15
Methods in community ecology
16
Required reading
  • Salt 1983 (pdf by e-mail)
  • J.H. Brown 1997. An Ecological Perspective on
    the Challenge of Complexity
  • http//webcache.googleusercontent.com/search?qcac
    heKrq4MRo4aRkJwww.nceas.ucsb.edu/nceas-web/proje
    cts/resources/ecoessay/brown/
  • P. Kareiva 1997. Why worry about the maturing of
    a science?
  • http//www.nceas.ucsb.edu/nceas-web/projects/resou
    rces/ecoessay/brown/kareiva.html

17
Goals of community ecology
  • Finding patterns, laws, generalizations that
    apply to diverse systems and convey understanding
    about those systems in general.
  • Gain sufficient understanding of communities to
    be able to predict community properties
    processes under certain conditions

18
Research Methods
  • Ecology (and community ecology in particular)
    began with inductive approaches to science
  • Accumulate observations, e.g., on diversity of
    local communities.
  • Generalizations will result from such
    accumulation
  • Morin Table 1.1, Figs. 1.1, 1.2
  • Result Reams of data Descriptions of
    patterns.
  • No hypotheses, no increased understanding of
    mechanisms how systems work

19
Research methods
  • Next step Hypothetico-deductive approach (phase
    1). Using simple mathematical models and
    observations.
  • Determine general properties hypothesize
    relationships among components
  • Formulate hypotheses into a simple mathematical
    model
  • Manipulate model, deduce new predictions
  • Attempt to verify prediction by observation
    (usually qualitative)
  • Niche width models and resource overlap see pp.
    57-58

20
Problems
  • Tended to look for confirmation of predictions
  • Predictions were often not risky
  • Observational data involve multiple processes
    that may also produce similar predicted results
  • Requires an assumption that all else is equal
  • Theory became esoteric and complex, data
    gathering and handling was rudimentary

21
Two approaches, two problems
  • Induction
  • little in the way of generality
  • much al fresco hackwork (Salt 1983)
  • H-D approach phase 1
  • general theory rarely confirmed
  • Mechanisms lacking
  • theory that was true but trivial, or false but
    profound (Henry Horn)

22
H-D approach phase 2 experimental ecology
  • Rigorous definition of pattern
  • Experimental tests of predictions
  • Control of other variables
  • Falsification of hypotheses
  • Multiple hypotheses
  • Salt (1983) three roles in science

23
Three roles
  • Observer Formulate hypotheses about how nature
    works
  • Theoretician Convert verbal explanations into
    mathematical model yielding new predictions
  • Experimentalist Design experimental tests of
    predictions, falsify some hypotheses

24
The process each activity is judged
25
Experiments
  • Action or operation undertaken to collect
    observations under a prearranged plan and
    defined conditions in order to discover something
    unknown or to test a hypothesis
  • Natural ambient conditions measure phenomena as
    they exist
  • Manipulative create conditions measure
    phenomena under known conditions

26
Manipulative experiments
  • Experimental units (e.u.) smallest unit to
    which a manipulation (treatment) is applied
  • Randomization every e.u. has an equal
    independent chance to receive each treatment
  • eliminate bias
  • e.u.s on average alike, except for treatments
  • Replication gt1 e.u. receives each treatment
    independently

27
Manipulative experiments
  • Pseudoreplication in data analysis, treating
    something that is not an e.u. as if it were
  • example effect of pesticide on plant growth
  • Measure yield / plant on n15 plants each

28
Manipulative experiments
  • Control treatment incorporating all natural
    variation except the factor of interest
    (treatment)
  • untreated
  • sham treated
  • Independence response of 1 e.u. is unrelated to
    the response of another
  • Interspersion spatial independence

29
What experiments can tell you
  • Manipulative
  • Laboratory
  • Field
  • Natural
  • hypothetical example altitudinal distributions
    of terrestrial salamanders Plethodon jordani (pj)
    Plethodon glutinosus (pg)
  • Experiments by N. Hairston

http//163.238.8.180/fburbrink/Field20Work/Alaba
maMississippi/index.htm
http//www.apsu.edu/amatlas/images/PgluAFS1copy.j
pg
30
A natural experiment - multiple mountains
31
Hypotheses
  • P. glutinosus excludes P. jordani
  • P. jordani P. glutinosus do best in different
    climates or on different substrates
  • range of P. jordani dependent on some other
    species (e.g., predator)
  • Does P. glutinosus affect P. jordani?
  • Cannot answer without manipulation

32
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33
Interpreting removal outcomes
  • Removal outcome 1
  • some interaction with P. glutinosus sets lower
    limit for P. jordani
  • mechanism?

34
Interpreting removal outcomes
  • Removal outcome 2
  • P. glutinosus has no effect on range of P.
    jordani
  • some other factor limits distribution
  • does not establish which other factor

35
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36
Interpreting addition outcomes
  • Addition outcome 1
  • P. glutinosus has no effect on P. jordani
  • P. jordani inhibits P. glutinosus?
  • some aspect of the environment excludes P.
    glutinosus ?

37
Interpreting addition outcomes
  • Addition outcome 2
  • interaction with P. glutinosus sets lower limit
    on P. jordani
  • mechanism?

38
Criticisms of experimental ecology
  • Experiments are unrealistic
  • that is their function
  • control multiple factors focus on hypothesis
  • Field experiments dont control all variables
  • true, but irrelevant
  • no experiment controls all variables
  • Experimental units are not identical
  • if they were, no need to replicate

39
Natural experiments
  • Snap shot experiments
  • find sites that differ and compare
  • e.g., observed salamander distributions
  • Trajectory experiments
  • find sites at which some perturbation occurs and
    compare change over time with that at sites where
    that perturbation has not occurred
  • known timing of change
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