Chapter 5: Biodiversity, Species Interaction, Population Control

Chapter 5: Biodiversity, Species
Interaction, Population Control
Interspecific Competition
Members of two or more different species
interact to gain access to the same limited
• Niches overlap; the greater the overlap, the
more intense the competition
• No two species can occupy the same niche for
very long; Competitive Exclusion
• Both species may suffer
Intraspecific Competition
Members of the same species interact to gain
access to the same limited resources
• Predator – prey relationship; 1 species feeds
directly on all or part of another species;
usually on live species
• Help sustainability (ex. – kelp-urchin-otter)
• Carnivores use either ambush or pursuit to
capture prey
• Ambush: camouflage is used; adapted by prey
as well
• Chemical warfare: used by spiders, snakes, to
paralyze prey
• Prey use adaptations such as speed, alert
systems (senses) , avoidance (ex. – shells),
mimicry and scare tactics
• Role in natural selection: weeding out the
weak, aged, sick in a population
• Coevolution may occur; changes in one
species gene pool leads to adaptive changes in
One species (the parasite) feeds on the body of,
or energy used by, another organism
• Parasite is much smaller than host
• May weaken but rarely kills host
• Some live in host (tapeworms) some attach to
outside of host (lampreys)
• Some have little contact with hosts (cowbirds)
• Coevolution can happen (malaria)
Interaction that benefits both species by
providing food, shelter, or some resource
• Pollinators
• Birds that eat parasites off skin of other
animals, also act as alarm system
• Clownfish – anemone
• Gut-inhabitant species
Interaction that benefits one species while other
is not affected
• Epiphytes such as orchids and bromeliads
Resource Partitioning
When species competing for similar resources
evolve traits that allow them to share
resources at different times, ways, or places
• Examples: warblers and honeycreepers
Populations differ in:
• Distribution
• Numbers
• Density
• Age structure
Population Dynamics studies changes in all the
above in response to environmental changes
3 Patterns of Distribution
• Clumping – example; desert vegetation
around springs; location & size varies with
availability of resources; offers advantages
• Uniform Distribution
• Random Distribution
Numbers vary cyclically
• Population Change = (births + immigration) –
(deaths + emigration)
• Age Structure: proportions of individuals in
various age groups
– Pre-reproductive
– Reproductive
– Post-reproductive
Indefinite Population Growth? No!
• Biotic Potential: large animals at a disadvantage;
low biotic potential
• Intrinsic Rate of Increase (r): rate at which
population would increase if unlimited resources
are available
• High r value: reproduce early, often, short
generation time, produce many offspring
• Scientific Principles of Sustainability – always
limits population growth
Environmental Resistance
Combination of all factors that limit population
• With biotic potential, it determines the Carrying
Capacity (k); the maximum population a habitat
can sustain
• Exponential growth: 1-2% increase; when
graphed, produces a “J” curve
• Logistic Growth: rapid exponential growth
followed by a leveling off; when graphed,
produces an “S” curve
Population Crash
• No logistic curve is achieved
• Brought on by a reproductive time lag in rates
of births and deaths
• Die-back occurs
• Sometimes when a population exceeds k, it
causes damages that reduce k (over-grazing in
the US)
Reproductive Patterns
• r-selected species: have many offspring, give
little or no parental care, are opportunists,
susceptible to population crash
• K-selected species: reproduce later in life,
produce small numbers of offspring, matire
slowly, longer life spans, parental protection,
logistic pattern
Genetic Diversity
Affects smaller populations:
• Founder Effect: a population colonizes a new
• Demographic Bottleneck: few individuals
survive a catastrophe
• Genetic Drift: random changes in gene
frequency → unequal reproductive success
• Inbreeding: increases frequency of defective
Population Density
Number of individuals per unit area or volume
• Density-Dependent Controls: predation,
infectious disease, competition
• High Density: successful reproduction, leads to
increased competition
• Abiotic Controls are density independent (ex. -
Types of Population Change
• Stable: population fluctuates slightly above
and below its carrying capacity
• Irruptive: occasional population explosion
followed by a crash to stable level; algae,
insects (summer – winter)
• Cyclic: follow a top-down or bottom-up
• Irregular: no recurring pattern
Humans not Exempt
• Irish potato famine
• Bubonic plague
Primary Succession
A gradual establishment of biotic communities
in lifeless areas where there is no soil in
terrestrial ecosystems and no bottom
sediment in an aquatic ecosystem
• Examples: bare rock from glacial retreat,
newly cooled lava, parking lot or highway,
newly created pond or reservoir
• Involves a pioneer species
Primary Succession
• Slow process
• Pioneer species begin soil formation (ex –
lichens and mosses)
• Followed by mid-successional plants (shrubs,
grasses, herbs)
• Late-successional plants (trees)
Secondary Succession
A series of communities or ecosystems with
different species develop in places containing
soil or bottom sediment
• Occurs where an ecosystem has been
disturbed, removed, or destroyed
• Include abandoned farmland, burned or cut
forests, heavily polluted streams, flooded land
Secondary Succession
• Both types of succession increase biodiversity
and thus the sustainability of communities
and ecosystems
• Environmental disturbances can set both
processes back
• Succession does not follow a predictable path
Stability in Living Systems
• Inertia (Persistence): the ability of a living
system to survive a moderate disturbance
• Resilience: the ability of a living system to be
restored through secondary succession after a
moderate disturbance
• Ecosystems are one or the other
• Tipping point comes into play (systems dealing
with multiple stresses)

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