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Species and Populations
Significant ideas
 A species interacts with its abiotic and biotic
environments, and its niche is described by these
 Populations change and respond to interactions with the
 Any system has a carrying capacity for a given species
 A species is a group of
organisms that share
common characteristics
and that interbreed to
produce fertile offspring.
 Humans, Giraffes, Pine
 Species are given scientific
name with genus and then
species (in italics)
 Humans Homo sapiens
 Wolf Canus lupus
Populations and Habitats
 Population: A group of
individuals of the same
species living in the same
area at the same time.
 Able to interbreed
 Snails in two different
ponds may breed with only
snails in each respective
 Populations can be
separated by geography and
eventually stop
 Form a new species this
 Habitat: The environment
where a species normally
 Includes Abiotic and Biotic
 Examples of habitats?
Abiotic Vs. Biotic
Abiotic (non-living)
 Atmosphere/Sunlight
 Climate
 Soil structure and
 Water chemistry
 Seasonality
 Level of Pollutants
Biotic (living) Factors
 Producers
 Consumers
 Decomposers
 Predation
 Parasitism
 Mutualism
 Disease
 Competition
 A group of populations living and interacting with each
other in a common habitat.
 Example: Tropical Rainforest- plants, animals, bacteria,
and fungi.
 A community of interdependent organisms and the
abiotic (physical) environment which they inhabit.
 As small as a drop of rainwater to as large as an ocean
 All ecosystems are affected by humans
 An organisms “occupation” or “job”. Its relationship to
its food and predators.
 Describes the particular set of abiotic and biotic
conditions and resources to which an organism or
population responds
 Example: Small fish in a coral reef share the same
habitat, but each species has a different niche. Each
population has a different “job” based on its shape,
size, color, behavior, and feeding habits.
Population Growth and Changes
 Exponential or Geometric Growth: Occurs when no
limiting factors slowing growth
 Usually produces a J-Curve
 Examples?
 Bacteria in a petri dish
 Humans
Limiting Factors: Reduce or stop
population growth
 Density-dependent limiting
factors: biotic factors that tend
to increase with increasing
population size.
 Density-Independent
limiting factors: tend to be
abiotic. Not related to
population density.
 Act as negative feedbacks that
lead to stability or regulation of
a population
 Internal factors act within a
species: limited food supply,
limited territory, limited fertility.
 External factors act between
species: Predation, disease.
 Would a higher population
density affect predator-prey
relationships? How? What
about spread of disease?
 Examples: weather,
climate, volcanic
eruptions, floods
 What would be a densityindependent factor for
Lynx and Snowshoe Hare
Density-dependent limiting factor.
Internal or external?
Population Curves
S-Curve reality
J-Curve Reality
Population Curves
 Boom and Bust pattern
 Population grows exponentially at
first and then suddenly collapses
 Collapses are called “diebacks.”
Often the population exceeds
carrying capacity before the
dieback occurs
 Start with exponential
growth, however above a
certain population size the
growth rate slows down
gradually until it’s constant.
 Growth slows down more in
larger populations.
 Density-independent or
 Density independent or
 Typical of microbes,
invertebrates, fish, and small
 Typical of large mammals
and humans
Carrying Capacity
 Carrying Capacity (K): Maximum population size
supported by ecosystem.
 Based on the two curves we just looked at, what
happens if a population exceeds its carrying capacity?
 Do you think humans have or ever will reach carrying
capacity? What evidence would support humans
reaching carrying capacity?
K- and r-strategists: Reproductive
 K and r are two variables that determine the shape of
the population growth curve.
 r = growth rate of the population
 K = carrying capacity
K-Selected Species
r-Selected Species
 Have small numbers of offspring
but invest large amounts of energy
in parental care.
 Have extremely large numbers of
offspring, but invest little or no
time raising them.
 Most offspring survive, long lives
 Reproduce quickly, but short lived
 Examples?
 Colonize new habitats rapidly
Large mammals
 Good competitors and population
is usually close to carrying
 Can outcompete r-strategists in
good conditions
 Usually exceed carrying capacity
and populations collapse.
 Predominate in unstable
 Examples?
Invertebrates and fish
What about us?
 …carrying capacity is determined jointly by human
choices and natural constraints. Consequently, the
question, how many people can the Earth support,
does not have a single numerical answer, now or
ever. Human choices about the Earth's human
carrying capacity are constrained by facts of nature
which we understand poorly. So any estimates of
human carrying capacity are only conditional on
future human choices and natural events." Joel
Survivorship Curves
 Shows the fate of a group
of individuals of a species.
 Type 1-K-strategists
 Type 2- r-strategists
 Type 3- Rare.
 Represents
species that has equal
chance of dying at any age.