Chapter 5 Biodiversity, Species Interactions and Population Control

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Chapter 5Biodiversity, Species Interactions and
Population Control
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Species Interact in major ways

• Interspecific competition 2 or more species
  interact to gain access to limited resources
• Predation prey/predator
• parasitism - parasite/host
• Mutualism benefits both species
• Commensalism benefits one species , no effect
  on the other

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Role of predation

• Cyclic changes sharp increases in number
  followed by seemingly periodic crashes
• Wolves controlling deer and moose populations
• Sheep and rabbits controlling plant growth

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Competition for resources

• the greater the overlap the more intense the
  competition
• Resource partitioning specialized traits allow
  species to use shared resources at different
  times
• Competitive exclusion intense copetition
  between 2 equal species, both suffer (one more
  than the other) by having reduced access to
  resources

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Population Dynamics

• characteristics of populations change in response
  to environmental conditions
• Size number of individuals
• Density number of individuals in a certain
  space
• Distribution spatial pattern clumping,uniform
  dispersion,
• random dispersion
• Age distribution structure - percentage of
  individuals in each age group

uniform
Clumping
random
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What limits population growth?

• Birth, death, immigration, emigration

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Population change

• (birth immigration) - (death emigration)
• dependent on resource availability or other
  environmental changes

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Intrinsic rate of increase

• rate at which a population could grow if it has
  unlimited resources
• always limits - light, water, space, nutrients
• High r reproduce early in life, short
  generation ie. reproduce many times many
  offspring house fly

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Carrying capacity - capacity for growth

• number of individuals of a given species that can
  be sustained indefinitely in a given area (K)
• determined by interaction between biotic
  potential and environmental resistance (factors
  that act jointly to limit a population)

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Population Dynamics and Carrying Capacity

• Basic Concept Over a long period of time,
  populations of species in an ecosystem are
  usually in a state of equilibrium (balance
  between births and deaths)
• There is a dynamic balance between biotic
  potential and environmental resistance

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Carrying Capacity (K)

• Exponential curve is not realistic due to
  carrying capacity of area
• Carrying capacity is maximum number of
  individuals a habitat can support over a given
  period of time due to environmental resistance
  (sustainability)

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Biotic Potential

• Ability of populations of a given species to
  increase in size
• Abiotic Contributing Factors
• Favorable light
• Favorable Temperatures
• Favorable chemical environment - nutrients
• Biotic Contributing Factors
• Reproductive rate
• Generalized niche
• Ability to migrate or disperse
• Adequate defense mechanisms
• Ability to cope with adverse conditions

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Environmental Resistance

• Ability of populations of a given species to
  increase in size
• Abiotic Contributing Factors
• Unfavorable light
• Unfavorable Temperatures
• Unfavorable chemical environment - nutrients
• Biotic Contributing Factors
• Low reproductive rate
• Specialized niche
• Inability to migrate or disperse
• Inadequate defense mechanisms
• Inability to cope with adverse conditions

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Population Density

• Population Density (or ecological population
  density) is the amount of individuals in a
  population per unit habitat area
• Some species exist in high densities - Mice
• Some species exist in low densities - Mountain
  lions
• Density depends upon
• social/population structure
• mating relationships
• time of year

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Reproductive Strategies

• Goal of every species is to produce as many
  offspring as possible
• Each individual has a limited amount of energy to
  put towards life and reproduction
• This leads to a trade-off of long life or high
  reproductive rate
• Natural Selection has lead to two strategies for
  species r - strategists and K - strategists

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r - Strategists

• Spend most of their time in exponential growth
• Maximize reproductive life
• Minimum life

K
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R Strategists

• Many small offspring
• Little or no parental care and protection of
  offspring
• Early reproductive age
• Most offspring die before reaching reproductive
  age
• Small adults
• Adapted to unstable climate and environmental
  conditions
• High population growth rate (r)
• Population size fluctuates wildly above and below
  carrying capacity (K)
• Generalist niche
• Low ability to compete
• Early successional species

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K - Strategists

• Maintain population at carrying capacity (K)
• Maximize lifespan

K
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K- Strategist

• Fewer, larger offspring
• High parental care and protection of offspring
• Later reproductive age
• Most offspring survive to reproductive age
• Larger adults
• Adapted to stable climate and environmental
  conditions
• Lower population growth rate (r)
• Population size fairly stable and usually close
  to carrying capacity (K)
• Specialist niche
• High ability to compete
• Late successional species

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Survivorship Curves

• Late Loss K-strategists that produce few young
  and care for them until they reach reproductive
  age thus reducing juvenile mortality
• Constant Loss typically intermediate
  reproductive strategies with fairly constant
  mortality throughout all age classes
• Early Loss r-strategists with many offspring,
  high infant mortality and high survivorship once
  a certain size and age

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Survivorship curves

• proportion of survivors of a particular species
  in a particular age group
• a)late loss type I - elephant
• b) early loss type II songbirds
• c) constant loss - intermediate reproductive
  strategies- starfish

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Population growth

• J-shaped - exponential growth curve, growth
  starts slowly then speeds up
• S - shaped curve- logistic growth curve - slow
  start, rapid exponential growth, levels off when
  K is reached

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Population cycles in nature

• relatively stable - slight fluctuation above and
  below carrying capacity, tropical rain forest
• erupt - high peak, crash - raccoons
• cyclic - boom and bust

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Effect of population density on population growth?

• Density Independent floods, drought, hurricane,
  habitat destruction, pesticide spraying
• Density dependent competition for resources,
  predation, disease infectious diseases plague
  in Europe

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Communities and ecosystems respond to
environmental change

• Primary succession- gradual establishment of
  biotic communities in life less areas where there
  is no soil in a terrestrial ecosystem or nobottom
  sediment in an aquatic ecosystem
• Secondary succession series of comunities or
  ecosystems with different species develop in
  places containing soil or bottom sediment

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Primary succession

• bare rock subject to weathering crumbles into
  particles, releasing nutrients
• Pioneer or early successional species (lichens or
  mosses)attach to rock and start the process of
  rock formation by secreting mild acids
• Mid successional plants grasses, herbs, small
  plants
• Late successional species trees that can tolerate
  shade

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Secondary succession

• ecosystem has been disturbed , removed or
  destroyed, some soil or bottom sediment remains
• abandoned farmland, burned or cut forests,heavily
  polluted streams, flooded lands

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Living systems are sustained through constant
change

• complex system of positive and negative feedback
  loops that interact to provide stability
• Inertia or persistence ability of a living
  system such as grassland or forest to survive
  moderate disturbances
• Resilence ability of a living system to be
  restored through secondary succession after a
  moderate disturbance

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Conservation Biology

• Investigate human impacts on biodiversity
• Develop practical approaches to maintaining
  biodiversity
• endangered species management, wildlife reserves,
  ecological restoration, environmental ethics

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Prevent premature extinction how ?

• Status of natural populations, species in danger
  of extinction
• Status of the functioning of ecosystems
• Measures taken to maintain habitat quality which
  will support wild species population

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Understand status of natural populations

• Measure current population size
• Determine how size will change with time
• Determine whether populations are sustainable

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Anthropogenic impact

• Fragmenting or degrading habitat, simplifying
  natural ecosystems, strengthening genetic
  resistance to pesticides, eliminating predators,
  introduce alien species, over harvesting,
  interfering with nutrient cycles

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Working with Nature

• Learn six features of living systems
• Interdependence
• Diversity
• Resilience
• Adaptability
• Unpredictability
• Limits

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Basic Ecological Lessons

1. Sunlight is primary source of energy
2. Nutrients are replenished and wastes are disposed
   of by recycling materials
3. Soil, water, air, plants and animals are renewed
   through natural processes
4. Energy is always required to produce or maintain
   an energy flow or to recycle chemicals

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Basic Ecological Lessons

1. Biodiversity takes many forms because it has
   evolved over billions of years under different
   conditions
2. Complex networks of and feedback loops exist
3. Population size and growth rate are controlled by
   interactions with other species and with abiotic
4. Organisms generally only use what they need

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Four Principles for Sustainable

1. We are part of, not apart from, the earths
   dynamic web of life.
2. Our lives, lifestyles, and economies are totally
   dependent on the sun and the earth.
3. We can never do merely one thing (first law of
   human ecology Garret Hardin).
4. Everything is connected to everything else we
   are all in it together.