Title: Population Ecology
1Population Ecology
2Populations
- Population ecology is the study of populations in
relation to the environment - A population is a group of individuals of the
same species that live in the same area
3Population Ecology Vocabulary
- To describe populations, we have to talk about
how they are situated - Density
- The number of individuals per unit area/volume
- Example 47 elephants/km2
- Dispersion
- The pattern of spacing among individuals in a
population - Clumped
- Uniform
- Random
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5Uniform
- Environmental conditions are uniform
- Causes COMPETITION or antagonism between
organisms (territoriality)
6Clumping
- Most common
- Reproductive patterns favor clumping
- Social behaviors lead to clumping
- Optimal density is usually intermediate (medium)
7Random
- No competition
- No tendency to group/clump
- Conditions are uniform
- Rarely happens!
8Estimating Population Size
- Rarely, it is possible to count the number of
species in a population - Usually, a statistical method is needed to
determine population size - The mark-recapture method can be used to estimate
the size of a population - Capture, mark, release
- Recapture and count
- Equation
- N Number marked x Total catch 2nd time
- Number of marked recaptures
9Factors That Influence Population Size
- There are 3 major factors that influence
population size - 1. the number of births
- 2. the number of deaths
- 3. the number of individuals that enter or
- leave a population
- - immigration
- individuals entering an existing population
- - emigration
- individuals leaving an existing population
10DEMOGRAPHICS
- In looking at populations, biologists must also
look at demographics (the vital statistics of a
population and how they change over time) - Birth rates
- Death rates
- Life tables
- Survivorship curves
- Reproduction rates
- Growth rates
- Age structures
11DEMOGRAPHICS
- One tool in demographics is to estimate the life
span of organisms - To do this they often create a life table, age
summary of a population - A cohort (group of individuals of the same age)
are studied to see what percentage of the
population dies - This can determine life expectancy, survivorship
at each age category, or male vs. female
survivorship
12Survivorship Curves
- A way to represent a life table is a survivorship
curve, a plot of the proportion of individuals
that survive at each age group - When discussing survivorship curves, there are 3
general categories
13Survivorship Curves
- Type I- live to old age die (most large
mammals) - Type II- constant mortality rate (rodents,
lizards, hydra) - Type III- high mortality at young age, but if
they survive they live a long life (sea turtles).
14DEMOGRAPHICS
- Another important aspect of demographics is
reproductive rates - For obvious reasons, biologists who study
reproductive rates only focus on females - Age of fertility
- Number of offspring for each age group
- Time of year
- Spawning cycles
- Reproductive tables summarize this data
15Life Histories
- Life history are traits that affect an organisms
schedule of reproduction and survival - Clutch size
- Number of offspring produced at each reproductive
episode - Semelparity
- A life history in which an organism spends most
of its energy in growth and development, expend
their energy in one large reproductive effort,
and then die - Many insects, annual plants, salmon, etc.
16Life Histories
- Iteroparity
- A life history pattern in which organisms produce
fewer offspring at a time over a span of many
seasons - Example humans, panda bears, etc.
17Life Histories (Semelparity vs. Iteroparity)
- Many factors contribute to the life history of an
organism - Finite resources
- Reproduction vs. survival
- Number and size of offspring
- Paternal investment in offspring
18POPULATION GROWTH MODELS
- Different models of how populations grow
19Formulas off your Cheat Sheet
- Rate dY/dt
- Generic expression for change of some variable
(Y) over time (t) - Population Growth dN/dt (B D)
- The change in population size (N) over time (t)
is the same as the birth rate (B) minus the death
rate (D) - Exponential Growth dN/dt rmax N
- The change in population size over time is equal
to the growth rate (rmax) multiplied with the
current population size
20Formulas off your Cheat Sheet
- Logistic Growth
- dN/dt rmax N (K-N)/K
- The growth rate over time is the same as
exponential growth adjusted for carrying capacity
(K)
21Types of Population Growth (start here)
- One of the biological imperatives is to reproduce
and pass on genetic material to succeeding
generations. - Yet population growth is controlled by the
environment and limited resources - This causes different patterns of population
growth
22Patterns of Population Growth
- Exponential Growth
- Occurs in ideal conditions with unlimited
resources - J shaped curve
- Example
- 1 bacterium (reproducing every 20 minutes) could
produce enough bacteria to form a 1-foot layer
over the entire surface of the Earth in 36 hours
23Exponential Growth
- Exponential growth is a useful model when
studying populations that are introduced into a
new, unfilled, environment - Recovery after a catastrophe
- Exponential Growth
- dN/dt rmax N
- rmax is the maximum rate of population growth for
the species
24Patterns of Population Growth
- Exponential growth cannot continue indefinitely
- It is characteristic of populations who are
entering a new environment OR those whose numbers
are rebounding from a catastrophic events
25Patterns of Population Growth
- Logistic Growth
- Pattern of population growth which takes into
account the effect of population density on
population growth - Occurs when resources become more scarce
- Characterized by an S-shaped curve
26Patterns of Population Growth
- dN/dt rmax N (K-N)/K
- Carrying capacity (K)
- The maximum number of individuals that a
particular environment can support over a long
period of time - Determined by such limiting factors as crowding
and food resources - Graph levels off at carrying capacity
- K-selected populations (equilibrial populations)
live near or at the carrying capacity
27Carrying Capacity
28K-strategists (Life history)
- Density stays near carrying capacity.
- Large, slow growing organisms
- Small population sizes
- Long life span slow maturation
- Few young/small clutch size
- Reproduce late in life
- Parental care
- Most large mammals endangered species
29r- strategists (Life history)
- Grow exponentially when environmental conditions
allow when conditions worsen, population size
plummets. - Short life span
- Reproduce early in life
- Many offspring/large clutch size
- Usually small in size
- Little or no parental care
- Bacteria, some plants, insects
30Environmental Factors
- Abiotic and biotic influences on population size
31Limiting Factors
- There are a number of factors that limit the size
of populations - Density-dependent limiting factors (depends on
the size of the population) - Density-independent limiting factors (does not
matter the size of the population)
32Density-Dependent Limiting Factors
- The effect of density-dependent limiting factors
intensifies as the population increases - Intraspecific competition
- Food, space, etc.
- Territoriality
- Predation
- Waste build up
- Disease (if caused by pathogen/contagious)
33Density-Independent Limiting Factors
- The occurrence and severity of density-independent
limiting factors are unrelated to population
size - Climate
- Disease (if not caused by pathogen/not
contagious) - Pollution
34The Interaction of Limiting Factors
- Density-dependent and density-independent
limiting factors often work together to regulate
the size of a population - Deer in snowy winter
- Starve from lack of food (density-dependent)
- Severity of winter/depth of snow determines
access to food (density-independent)
35Population Dynamics
- Population dynamics is the study of the
environmental factors that cause variations in
the population size - Looks at fluctuations in population over time to
examine stability - Immigration and emigration also affect population
- Metapopulations are when you have several
interconnected populations
36Boom-and-bust cycle
- Another phenomena that affects population are
predator-prey relationships. - Each population is interdependent and causes a
boom-and-bust cycle - The prey population increases which causes the
predator population to increase - The prey are over hunted and their population
crashes - This causes the predator population to crash
- Now, with fewer predators, the prey population
can again increase (recovery gives a geometric
increase)
37 Boom-and-Bust Cycles
38Human Population Growth
39Increase in Human Population
- Agricultural Revolution - Major period of
population growth began when humans started to
cultivate crops and domesticate animals - Industrial Revolution Improved food production
and distribution - Health Care germ theory lead to improved
hygiene, better waste removal and water treatment
40Decrease in Human Population
- Plague disease that greatly reduces the size of
population (Black Plague in 1300s reduced the
population in England by 50) - Famine a severe food shortage causing starvation
and death (Potato Famine of 1840s/China
1870-1890) - War death by combat, disease, cut off from food
supply (Germany 1618-1648/WWI/WWII)
41Human Population Growth
- The human population is unlike any other organism
- Since about 1650, we have remained in an
exponential population increase - Population increases by about 201,000 people/day
worldwide
42Human Population Growth
43Human Population Growth
- Even though there is a tremendous increase in
human population, it is not evenly distributed
around the globe - Regional areas have different population trends
- Some regions have stable regional human
populations (birth rate is the same as death
rate) - Other regions show incredible growth rates
44Industrialized Nations
- An emerging nation usually has a very high birth
rate, but also a high death rate (disease, lack
of modern medical treatment, famine) - An industrialized nation usually has a low death
rate, but also a low death rate - Moving from an emerging nation to an
industrialized nation is known as a demographic
transition
45Human Population Growth
- In the 1950s, mortality rates began to rapidly
drop (advances in medicine and sanitation) - Yet, the birth rates have not always dropped
- Has caused a huge increase in population in some
nations - About 80 of the worlds population lives in
emerging nations
46Age Structure
- One way to determine human population growth is
to look at the nations age structure, relative
number of individuals at each age - By looking at the age structure of a population,
you can determine the population growth
47Age-Structure Diagrams
48Human Population Growth
- Implications of exponential human population
growth - Lack of food supplies
- Lack of space
- Lack of natural resources (metals, fossil fuels,
etc) - Lack of sites for waste disposal
- Ecologists cannot agree on a carrying capacity
for Earth (2 40 billion) - Are we going to reach carrying capacity through
individual choices and/or government programs? - OR
- Is Earths population going to level off as a
result of mass deaths?