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Ecosystems: Populations and Succession

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Endangered Species Act. Threatened species whose populations are declining rapidly ... Endangered if the population is near what scientists believe to be ... – PowerPoint PPT presentation

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Title: Ecosystems: Populations and Succession


1
Chapter 4
  • Ecosystems Populations and Succession

2
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3
Population Dynamics
  • Each species in an ecosystem exists as a
    population
  • Population reproducing group
  • Population equilibrium balance between births
    and deaths

4
Population Growth Curves
  • Exponential Increase
  • Population explosion
  • When the size of a population is plotted over
    time, two basic kinds of curves can be seen
    S-curves and J-curves

5
Two types of growth curves
6
Biotic Potential versus Environmental Resistance
  • Biotic potential the ability of populations to
    increase
  • Recruitment survival through the early growth
    stages

7
Two strategies
  • 1. Produce massive numbers of young, with little
    or no care result in low recruitment despite
    high biotic potential
  • Low recruitmenthigh mortality
  • 2. Lower reproductive rate, but then care and
    protect young to enhance recruitment

8
Carry capacity
  • Usually limited by environmental resistance
    biotic and abiotic factors that limit population
    increase
  • The upper limit of any particular animal that an
    ecosystem can support is called the carrying
    capacity

9
Population balance
  • Population balance is a dynamic balance
  • Additions (births) and subtractions (deaths) are
    occurring continually and the population may
    fluctuate around a median

10
Density Dependence and Critical Number
  • Population density the number of individuals
    per unit area
  • Density dependent environmental resistance
    becomes more intense as population density
    increases
  • Critical number the minimum population base
    that survival and recovery of a population
    depends on

11
Endangered Species Act
  • Threatened species whose populations are
    declining rapidly
  • Endangered if the population is near what
    scientists believe to be the critical number

12
Mechanisms of Population Equilibrium
  • Many factors may cause mortality in a population,
    but those that are density dependent are capable
    of actually regulating the population, keeping it
    around an equilibrium
  • Top-down regulation control by predation
  • Bottom-up regulation control occurs by the
    scarcity of some resource

13
Population control
  • Predator Prey dynamics

14
  • Parasites also tend to be density dependant

15
Plant Herbivore Dynamics
  • Overgrazing eating of plants faster than they
    can grow
  • Ex An unchecked population can explode, over
    graze then crash as a result of starvation
  • Predator Removal (elimination of predators)

16
Predator Removal
  • Keystone Species plays a critical role in
    maintaining ecosystem biotic structure
  • Example starfish on the rocky pacific northwest
    intertidal zone

17
Competition
  • Niches overlap when two species compete for the
    same scare resource
  • Competitive exclusion elimination of one of the
    species due to competition
  • Interspecific competition competition between
    members of different species

18
Territoriality
  • Protecting and defending an area of land from
    which adequate food resources can be obtained in
    order to rear a brood successfully
  • Usually against members of same species
    intraspecific competition

19
Introduced species
20
Introduced species
  • American Chestnut chestnut blight brought in on
    Chinese chestnut
  • Pests inscts, cats, goats, zebra mussel
  • Plants
  • Water hyancinth an escaped ornamental plant in
    Florida is now under maintenance control

21
Introduced plant species
22
Lessons
  • 1. The regulation of populations is a matter of
    complex inactions among the members of the biotic
    community
  • 2. The relationships are specific to the
    organisms in each particular ecosystem

23
Remedies?
  • Introduction of a natural enemy
  • Do single natural enemies exist?
  • We they fit in a survive the new ecosystem?

24
Definitions
  • Genetic variation genetic differences among
    individuals
  • Gene pool All the DNA of a species
  • Biological evolution change in the gene pool of
    a species over the course of generations
  • Selective pressures factors play a role in
    determining if an individual survives and
    reproduces or is eliminated

25
Natural Selection
  • Every factor of environmental resistance is a
    selective pressure resulting in the survival and
    reproduction of those individuals with a genetic
    endowment that enables them to cope with their
    surroundings.
  • Constant selection in nature
  • A modification of the gene pool towards features
    that enhance survival and reproduction within the
    existing biotic community and environment.

26
Darwin
  • Survival of the fittest
  • Survival of those individuals having traits that
    best enable them to cope with the biotic and
    abiotic factors of their environment.
  • Biological Evolution the modification of the
    gene pool that occurs through natural selection
    over the course of many generations

27
Fitness
  • Features that adapt an organism for survival and
    reproduction

28
Adaptations
  • Coping with climate
  • Obtaining food and water / nutrients
  • Escaping or protecting against predators
  • Resistance to disease or parasites
  • Finding or attracting mates reproduction
  • Migrating
  • Dispersing seeds

29
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30
Selective Pressures
31
Limits to change species only have three
alternatives
  • Adaptation adapt to new conditions
  • Migration migrate to a new area
  • Extinction

32
Will a population survive a new condition key
variables
  • Geographic distribution
  • Specialization to a given habitat or food supply
  • Genetic variation within the gene pool of the
    species
  • Reproductive rate relative to the rate of
    environmental change

33
Factors affecting survival of a species
34
Speciation
  • The final product may be so different from the
    population that started the process that it is
    considered a different species

35
New species
  • Two or more species can develop from one if you
    have reproductive isolation

36
Ecological Succession
  • The phenomenon of transition from one biotic
    community to another
  • Primary succession initial invasion then
    progression form one biotic community to the next
  • Secondary succession - reinvading an area after
    clearing by fire or humans

37
Secondary succession
38
Aquatic succession
  • Lakes and ponds are gradually filled in
  • The climax community may be a bog or a forest

39
Fire and Succession
  • Fire is a natural and important abiotic factor
  • Periodic fires are instrumental in maintaining a
    balance in favor of pines, grasses, or redwood
    trees
  • Ecosystems that depend on recurrence of fire to
    maintain existing balance are now referred to as
    fire climax ecosystems

40
Nonequilibrium Systems
  • Disturbances such as fires, floods, windstorms
    and droughts are important in structuring
    ecosystems
  • They remove organisms, reduce populations, and
    create opportunities for other species to
    colonize the ecosystem

41
Carry Capacity
  • The maximum population that a given habitat can
    support without the habitat being degraded over
    the long term

42
One question
  • What is the earths carrying capacity for humans?
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