Biology Ecology 2

Front 1

Population ecology

Back 1

The study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size

Front 2

Density

Back 2

- The number of individuals per unit area or volume
- The result of an interplay between processes that add individuals to a population (births and immigration) and those that remove individuals (deaths and emigration)

Front 3

Dispersion

Back 3

The pattern of spacing among individuals within the boundaries of the population

Front 4

Population size can be estimated by either:

Back 4

- extrapolation from small samples
- an index of population size ( e.g. # nests etc.)
- the mark-recapture method

Front 5

Patterns of Dispersion

Back 5

- Clumped
- Uniform
- Random

Front 6

Clumped Dispersion

Back 6

- Individuals aggregate in patches
- May be influenced by resource availability and behavior - Most common in nature

Front 7

Uniform Dispersion

Back 7

- Individuals are evenly distributed
- May be influenced by social interactions such as territoriality

Front 8

Random Dispersion

Back 8

- The position of each individual is independent of other individuals
- Occurs in the absence of strong attractions or repulsions

Front 9

Demography

Back 9

The study of the vital statistics of a population and how they change over time
-Death rates and birth rates are of particular interest to demographers

Front 10

Life Table

Back 10

- An age-specific summary of the survival pattern of a population
- Best made by following the fate of a cohort

Front 11

Cohort

Back 11

- A group of individuals of the same age

Front 12

Survivorship Curves

Back 12

A graphical way of representing the data in a life table

Front 13

Type 1 Survivorship Curves

Back 13

- Low death rates during early and middle life, then an increase among older age groups – e.g. humans

Front 14

Type 2 Survivorship Curves

Back 14

- The death rate is constant over the organism’s life span – squirrels, some annuals, some lizards, squirrels etc

Front 15

Type 3 Survivorship Curves

Back 15

High death rates for the young, then a slower death rate for survivors – long lived-plants, fish – organisms that produce large numbers of young

Front 16

Reproductive table

Back 16

- Fertility schedule, is an age-specific summary of the reproductive rates in a population – varies greatly depending upon species
- It describes reproductive patterns of a population

Front 17

Life History

Back 17

- An organism’s life history comprises the traits that affect its schedule of reproduction and survival:
- The age at which reproduction begins
- How often the organism reproduces
- How many offspring are produced during each reproductive cycle
- Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organism

Front 18

Semelparity

Back 18

Big-bang reproduction, species reproduce once and die e.g. salmon

Front 19

Iteroparity

Back 19

Repeated reproduction, species produce offspring repeatedly

Front 20

Semelparity v. Iteroparity

Back 20

- Highly variable or unpredictable environments likely favor big-bang reproduction, while dependable environments may favor repeated reproduction
- Not just two life history types since many organisms have a combination of both – reproduce repeatedly but large numbers e.g. oak tress and sea urchins

Front 21

Trade-offs between survival and reproduction

Back 21

- Some plants produce a large number of small seeds, ensuring that at least some of them will grow and eventually reproduce (ex: Dandelion)
- Other types of plants produce a moderate number of large seeds that provide a large store of energy that will help seedlings become established (ex: Coconut)

Front 22

The exponential model describes population growth in an idealized, unlimited environment

Back 22

- It is useful to study population growth in an idealized situation
- help us understand the capacity of species to increase and the conditions that may facilitate this growth
- If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate

Front 23

Zero Population Growth

Back 23

Occurs when the birth rate equals the death rate

Front 24

Population size equation

Back 24

rN = delta N / delta t

N = population size
t = time
r = per capita rate of increase

Front 25

Exponential Population Growth

Back 25

- Population increase under idealized conditions (J-curve)
- Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase

Front 26

Carrying Capacity

Back 26

- (K) is the maximum population size the environment can support
- Exponential growth cannot be sustained for long in any population
- A more realistic population model limits growth by incorporating carrying capacity

Front 27

Logistic Population Growth Model

Back 27

- The per capita rate of increase declines as carrying capacity is reached
- Some population overshoot K before settling down to a relative stable density

delta N / delta t = r(max)N x ((K-N)/K)

Front 28

Problems with the Logistic Population Growth Model

Back 28

- Some populations fluctuate greatly and make it difficult to define K
- Some populations show an Allee effect, in which individuals have a more difficult time surviving or reproducing if the population size is too small e.g. plant on its own withstanding excessive wind
- The logistic model fits few real populations but is useful for estimating possible growth

Front 29

K-selection

Back 29

Density-dependent selection, selects for life history traits that are sensitive to population density e.g. mature tress in an old forest – living at a density near limit of K

Front 30

r-selection

Back 30

Density-independent selection, selects for life history traits that maximize reproduction e.g. organisms in disturbed habitats
- K or r selection represent two extremes in a range of actual life histories

Front 31

Two general questions about regulation of population growth:

Back 31

- What environmental factors stop a population from growing indefinitely?
- Why do some populations show radical fluctuations in size over time, while others remain stable?
- Much practical info:
- E.g. farmer wants to stop growth of invasive weed/ reduce abundance of insect pest
- E.g. ecologist wants to know what are appropriate habitats/feeding grounds for endangered species etc.

Front 32

Density-independent populations

Back 32

- Birth rate and death rate do not change with population density – e.g. when organisms die due to drought stress

Front 33

Density-dependent populations

Back 33

- Birth rates fall and death rates rise with population density – e.g. reduced reproduction rates due to competition for resources

Front 34

Equilibrium density

Back 34

Birth rate and death rate cancel each other out, no population growth

Front 35

Density-dependent Population Regulation

Back 35

- Density-dependent birth and death rates are an example of negative feedback that regulates population growth
- They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors (physiological factors – aggressive behavior, stress)

Front 36

In many vertebrates & some invertebrates, competition for territory may limit density

Back 36

- Cheetahs are highly territorial, using chemical communication (mark their territory) to warn other cheetahs of their boundaries
- Oceanic birds exhibit territoriality in nesting behavior – nest on rocky islands to avoid predators – can find suitable nest site up to certain density only. Birds that do not obtain a nesting site do not reproduce

Front 37

Disease on Population Density

Back 37

- Population density can influence the health and survival of organisms
- In dense populations, pathogens can spread more rapidly

Front 38

Predation on Population Density

Back 38

- As a prey population builds up, predators may feed preferentially on that species

Front 39

Toxic Wastes on Population Density

Back 39

- Accumulation of toxic wastes can contribute to density-dependent regulation of population size

Front 40

Population Dynamics

Back 40

- Study that focuses on the complex interactions between biotic and abiotic factors that cause variation in population size
- E.g. Hirta Island sheep do well when weather good but drop off in numbers when weather bad  weakens sheep and reduces food availability

Front 41

Population Cycles

Back 41

- Some populations undergo regular boom-and-bust cycles
- Lynx populations follow the 10 year boom-and-bust cycle of hare populations
- Three hypotheses have been proposed to explain the hare’s 10-year interval
- The hare's population cycle follows a cycle of winter food supply
- The hare's population cycle is driven by pressure from other predators (supported)
- The hare's population cycle is linked to sunspot cycles (supported)

Front 42

Human Population Growth

Back 42

- No population can grow indefinitely, and humans are no exception
- The human population increased relatively slowly until about 1650 and then began to grow exponentially
- Though the global population is still growing, the rate of growth began to slow during the 1960s

Front 43

Maintain Population Stability

Back 43

- Regional human population can exist in one of two configurations:
- Zero population growth = High birth rate – High death rate
- Zero population growth =Low birth rate – Low death rate

Front 44

Demographic Transition

Back 44

- The move in the human population from high death and birth rates toward low death and birth rates
- The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women
- Most of the current global population growth is concentrated in developing countries

Front 45

Age Structure

Back 45

- The relative number of individuals at each age
- Age structure diagrams can predict a population’s growth trends
- They can illuminate social conditions and help us plan for the future

Front 46

Infant Mortality and Life Expectancy

Back 46

- Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition

Front 47

Global Human Carrying Capacity

Back 47

- How many humans can the biosphere support?
- The carrying capacity of Earth for humans is uncertain
- The average estimate is 10–15 billion

Front 48

Ecological Footprint Concept

Back 48

- summarizes the aggregate land and water area needed to sustain the people of a nation
- It is one measure of how close we are to the carrying capacity of Earth
- Countries vary greatly in footprint size and available ecological capacity
- Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes

Front 49

1

Back 49

1

Front 50

1

Back 50

1