BI111 Lecture 11: Lesson 11

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9 Feb 2017
School
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Ecology
Ecologists study levels of organization ranging from individual organisms to the biosphere
Study of the interactions between organisms (biotic) and their environments (abiotic)
Testing Hypotheses
Ecologists use experimental or observational data
o Field of laboratory studies used to test predictions by manipulating variables
o Data collected about "natural experiments" do not require manipulations
Sometimes hypotheses framed in mathematical models
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o Allows computer models to simulate natural events and large-scale experiments
Overarching goal of ecology is to understand the causes and consequences of changes of
population/ community structure
What characters to study?
Geographic range/ habitat
Population size
Population density
Population dispersion
Age structure
Generation time
Sex ratio
Proportion of individuals in reproductive condition
Geographic Range
Geographic range: overall spatial boundaries within which a population lives
Habitat: specific environment in which a population lives, as characterized by its biotic and abiotic
features
Estimating Population Size
Often a difficult task
o Too many?
o Cryptic?
Mark-Recapture methodology is one solution : selectively marking individuals releasing them into
population
Mark-Recapture study
Step 1: Capture a random sample of individuals (n1) that are marked
Step 2: Release marked individuals back into the population
Step 3: Capture a second random sample of Individuals (n2), some of whom are marked (n2m)
Step 4: Calculate initial population size(x) using the formula n1/x=n2m/n2
Assumptions of Mark-Recapture
Random sample?
Marking has no effect on survival or probability of being resampled later
Marked individuals have time to mix with unmarked individuals before second sample
Marks are not lost
Population is "closed"
o No births, deaths, immigration or emigration
Calculation
Population Density and Body Size
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Body mass(kg)
-Relationship between size and density often indicates information about resources used
-Individuals that are large are found at small densities, and small individuals are found at large densities
-Small organisms can easily survive in a place with resources than a group of large organisms
Population Dispersion
Spatial distribution of individuals within the geographic range
Dispersion Patterns
Influenced by:
o Distribution of resources in environment/ Landscape features
o Habitat requirements of each individual
o Social structure of species
o Dispersal capacity/mode of reproduction of species
o Presence/absence of other species
Random Distribution
Distance between individual is "random" with respect to each other's location
o Individuals neither attract nor repel one another
Rarest type
Found in homogenous environments
Seeds of a dandelion, seeds spread out over lawn and no matter where they land they have a
change to develop into a new dandelion plant
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