Population and Community Ecology

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Chapter 6

• Population and Community Ecology

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New England Forests Come Full Circle

• 1620
• Over next 200 years settlers
• Deforestation peaked in 1800s 80 of New
  England forests were cleared
• Bw 1850-1950
• Abandoned farmland slowly recovered resilient
  area
• This created an ever-changing ecosystem

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Nature exists at several levels of complexity
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Population Ecologists Study the Factors that
Regulate Population Abundance and Distribution

• Population ecology the study of factors that
  cause populations to increase or decrease
• Why is this important?

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Population Characteristics

• Population size (N)- the total number of
  individuals within a defined area at a given time
• Population density- the number of individuals per
  unit area at a given time
• Population distribution- how individuals are
  distributed with respect to one another

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Population Characteristics

• Population sex ratio- the ratio of males to
  females
• Population age structure- how many individuals
  fit into particular age categories

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Factors that Influence Population Size

• Density-dependent factors- the size of the
  population will influence an individuals
  probability of survival
• Gause
• Limiting resource
• Carrying capacity (K)
• Density-independent factors- the size of the
  population has no effect on the individuals
  probability of survival

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Population Growth Rate

• Population growth models
• Growth rate - the number of offspring an
  individual can produce in a given time period,
  minus the deaths of the individual or offspring
  during the same period
• Intrinsic growth rate - under ideal conditions,
  with unlimited resources, the maximum potential
  for growth
• Under less ideal conditions

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Exponential Growth Model

• Exponential growth model formula
• What results? ? J-shaped curve
• However

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Logistic Growth Model

• Logistic growth- when a population whose growth
  is initially exponential, but slows as the
  population approaches the carrying capacity
• Produces - S-shaped curve
• Problem

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Variations of the Logistic Model

• Populations do not always level off at carrying
  capacity
• Overshooting K population becomes larger than
  the K
• Result?
• Ie. reindeer on St. Paul Island in Alaska

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From Environment Boom-Or-Bust Population Cycles

• Boom-or-Bust Population Cycles
• Not well understood
• Ie. Lemmings and red grouse populations

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Population Oscillations

• Predator-Prey Relationships
• Lynx and Hares (R)
• Wolves and moose

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Reproductive Strategies

• K-selected species- the population of a species
  that grows slowly until it reaches the carrying
  capacity.
• Ex. elephants, whales, and humans
• R-selected species- the population of a species
  that grows quickly and is often followed by
  overshoots and die-offs
• Ex. mosquitoes and dandelions

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Survivorship Curves

• Species have different patterns of survival over
  time
• 3 basic curves
• Type I
• Type II
• Type III

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Metapopulations

• Metapopulations- a group of spatially distinct
  populations that are connected by occasional
  movements of individuals between them
• Movement via corridors
• Connections important

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Community Ecology

• Factors to determine distribution of species
• Species fundamental niche
• Ability to disperse to an area
• Interactions with other species
• Community ecology study of the interactions of
  organisms which determine the survival of a
  species in a habitat

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Competition

• Competition- the struggle of individuals to
  obtain a limiting resource
• Gauses Competitive Exclusion Principle

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From EnvironmentAnoles in FL Example

• Green Anole and Brown Anole
• Fundamental niches of 2 lizards initially
  overlapped
• Brown anole eventually out-competed the green
  anole ? reduced the green anoles realized niche

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Resource Partitioning

• Resource partitioning when 2 species divide a
  resource based on differences in the species
  behavior or morphology
• Species in nature reduce resource overlap via
• Temporal resource partitioning
• Spatial resource partitioning
• Morphological resource partitioning

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Predation

• Predation- the use of one species as a resource
  by another species
• Organisms of all sizes can be predators
• Predators can be grouped
• True predators
• Herbivores
• Parasites
• Pathogens parasites that cause disease
• Parasitoids
• Awesome video http//www.youtube.com/watch?vnZZy
  JQNmOV8

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Mutualism

• Mutualism- A type of interspecific interaction
  where both species benefit
• Examples
• Plants and pollinators
• Image Acacia trees and ants
• Lichen
• Coral reefs

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Commensalism

• Commensalism- a type of relationship in which one
  species benefits but the other is neither harmed
  nor helped
• Examples

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Overview of Interspecific Interactions

• Symbiotic relationship relationship of 2
  species that live in close association with each
  other
• Includes commensalism, mutualism and parasitism

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Keystone Species

• Keystone species- a species that plays a role in
  its community that is far more important than its
  relative abundance might suggest
• Usually not the most abundant or major energy
  producers
• Roles include
• Predators
• Sources of food
• Mutualistic
• Providers of some other essential service

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Keystone SpeciesThe Gray Wolf

• Where wolves were hunted to extinction ?
  populations herbivores increased explosively
• Caused overgrazing ? some plant species
  disappeared
• Many insects were lost
• Indiana and Montana- hunting of gray wolf ok

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Primary Succession

• Primary succession- occurs on surfaces that are
  initially devoid of soil
• Process
• Bare rock is colonized by organisms ? secrete
  acids

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Secondary Succession

• Secondary succession- occurs in areas that have
  been disturbed but have not lost their soil
• Follows events like forest fires, hurricanes,
  abandoned fields

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Climax Stage

• Climax stage (community) the community
  scientists used to believe ended succession
• Characteristics
• Complex structures many species interactions
• Narrow niches
• High species diversity

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Aquatic Succession

• Lakes are filled with sediment
• Slowly become terrestrial habitat
• Explain the process

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Factors that determine species richness

• Latitude
• Time
• Habitat size and distance from habitat from
  source of colonizing species
• Basis for the Theory of Island Biography (next
  slide)

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Theory of Island Biogeography

• Theory of island biogeography- the theory that
  explains that both habitat size and distance
  determine species richness
• Larger habitats contain more species
• Why?
• Further from colonizing community ?the less
  species