Data Analysis and Mathematical Models
 The structure of a community is described in terms of
species composition and diversity
 Communities are comprised of different populations
of organisms that interact with each other in negative
or positive ways
 The physical structure of a community is affected by
abiotic factors and also the spatial distribution of
organisms
 The mix of species in terms of both the number of
individuals and the diversity of the species defines the
structure of the community
 Predator/prey
relationships: Snowshoe
Hare and Lynx
 Changes in hare pop. is
followed by similar changes
in lynx pop. – predation
limits hare pop. and food
supply limits lynx pop.
 Fluctuation cycles are
commonly observed
between predator and prey
 Symbiotic Relationships
 Mutualism (+,+)
 Acacia trees provide food
& housing for ants; in
exchange, resident ants
kill any insects or fungi
found on the tree and crop
veg to increase sun
exposure for tree
 Lichen – algae provide
sugar from
photosynthesis; fungi
provide minerals, water,
attachment and protection
 Commensalism (+,0)
 Birds build nests in tree
(benefit from protection)
the tree gets no benefit
or harm
 Egrets gather around
cattle; birds get to eat
insects that swarm
around cattle; cattle are
neither helped or
harmed
 Parasitism (+,-)
 Tapeworm live in the
digestive tract of
animals, stealing
nutrients from the host
 http://youtu.be/rLtUkW5Gpk
 Introduction of Species
 Competitive Exclusion
occurs when two species
compete for exactly the
same resources (they
occupy the same niche),
one is likely to be more
successful. One species
outcompetes the other and
eventually the second
species is eliminated from
the area
 http://youtu.be/rZ_up40F
ZVw
 Resource Partitioning
occurs when species
coexist in spite of
apparent competition for
the same resources
 Species do this by
occupying slightly
different niches
 Which species of
paramecia outcompetes
the other?
 Paramecium aurelia
 Size is usually designated
as N (total number of
individuals)
 Density – total number
of individuals per area or
volume
 Dispersion – how
individuals in a
population are
distributed
 Age structure – is a description of the abundance of
individuals of each age
 Rapid growth – many young, few elderly; developing
countries
 Slow growth – larger at the bottom that slowly narrow; the
US
 Zero growth – tiers of equal width; Italy
 About 1,000 years ago
the human population
began population
growth thanks to
increasing the carrying
capacity of our
environment
 Increase in food
supply
 Reduction in disease
 Reduction in human
waste
 Expansion of habitat
 Survivorship Curves
describe how mortality
of individuals in a
species varies during
their lifetimes
 3 types of curves
 Type 1
 Type 2
 Type 3
 Type 1 Survivorship
describe species in which
most individuals live to
middle age; after that
mortality is high
 Examples: Humans,
Elephants
 Type 2 Survivorship
describes organisms in
which the length of
survivorship is random,
that is, the likelihood of
death is the same at any
age – constant death rate
 Examples: Rodents and
invertebrates
 Type 3 Survivorship
describe species in which
most individuals die
young, with only a
relative few surviving to
reproductive age and
beyond
 Examples: oysters,
plants, free-swimming
larvae, frogs
 Biotic Potential is the
maximum growth rate of a
population under ideal
conditions
 Take into consideration the
following:
 Age at reproductive




maturity
Clutch size
Frequency of reproduction
Reproductive lifetime
Survivorship of offspring
to reproductive maturity
 Limits to Growth
 Density-Dependent
factors are those factors
whose limiting effect
becomes more intense
as the population
density increases
 Examples – parasite &
disease transmission;
competition for
resources; predation
 Limiting Growth Factors
 Density-Independent
factors occur
independently of the
density of the
population
 Examples – natural
disasters such as fires,
earthquakes, volcanic
eruptions; extreme
climates such as storms
and frosts
 Exponential Growth in a
population occurs
whenever the reproductive
rate is greater than zero.
 Producing a J shaped curve
 G=rN
 G stands for growth, r
stands for the per capita
rate of increase, and N
stands for the population
size
 Logistic Growth occurs when limiting factors restrict the size
of the population to the carrying capacity of the habitat
 Producing a S shaped curve
 G=rN*(K-N)/K
 K stands for the carrying capacity; as N approaches K the
growth rate is slowed, eventually reaching zero growth
 Exponential and logistic growth patterns are
associated with two kinds of life-history strategies:
 R-selected species
 K-selected species
 R-selected species –
 Rapid growth (J shaped
curve)
 Opportunistic species –
grasses and insects
 Quickly invade a habitat
and reproduce
immediately (after
reproducing they die)
 Produce many offspring
that are small, mature
quickly and require little if
any parental care
 K selected species
 Population size remains
relatively constant at
carrying capacity, K – s
shaped curve
 Produce few offspring
that are larger in size
and require extensive
parental care
 Reproduction occurs
repeatedly during their
lifetime