Chapter 5: Biodiversity, Species
Interaction, Population Control
HOW DO SPECIES INTERACT?
Interspecific Competition
Members of two or more different species
interact to gain access to the same limited
resources
• 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
Predation
• 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
Predation
• 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
Predation
• Coevolution may occur; changes in one
species gene pool leads to adaptive changes in
another’s
Parasitism
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)
Mutualism
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
Commensalism
Interaction that benefits one species while other
is not affected
• Epiphytes such as orchids and bromeliads
NATURAL SELECTION REDUCES
COMPETITION
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
LIMITS OF POPULATION GROWTH
Characteristics
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
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
growth
• 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
habitat
• Demographic Bottleneck: few individuals
survive a catastrophe
• Genetic Drift: random changes in gene
frequency → unequal reproductive success
• Inbreeding: increases frequency of defective
genes
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
regulation
• Irregular: no recurring pattern
Humans not Exempt
• Irish potato famine
• Bubonic plague
• AIDS/HIV
ECOLOGICAL SUCCESSION
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)