Ecology exam 2

Populations have properties that cannot be applied to

Populations have properties that cannot be applied to

individuals

Demographics deals with statistical properties and trends in

populations

Density

the number of organisms per unit area volume

Natality

The reproductive output of a population (birth rate)

Mortality

the death of organisms in a population

Immigration

the number of organisms moving into the area occupied by the population

Emigration

the number of organisms moving out of the area occupied by population

Density is a

pattern

Natality, Mortality, Immigration, and Emigration are all

processes

Cohort life table

an age-specific summary of mortality rates operating on a ———- (will give it away) of individuals

Examples of cohorts include

an entire population, just males, individuals born in the same year, etc.

Standardized symbols used in life tables (x)

age

Standardized symbols used in life tables (Nx)

Number alive at age x

Standardized symbols used in life tables (Lx)

Proportion of organisms surviving from start of life table to age of x

Standardized symbols used in life tables (Dx)

number of dying organisms during the age interval of x to x+1

Standardized symbols used in life tables (Qx)

Per capita rate of mortality during the age interval x to x+1

for per capita rates, it is better to plot population data on a

logarithmic scale

survivorship

percentage of original population that survives to a given age

Life table data is often plotted as survivorship curves

number of survivors from a focal cohort plotted against age

Type 1 curve (top on survivorship curves)

Relatively low mortality when young, high mortality in post reproductive years

Type 2 curve (middle of survivorship curves)

straight curve, individuals are likely to die at any age

Type 3 curve (lowest on survivorship curves)

produce vast number of offspring, few survive to reproduce, once established mortality is low

type ___ curves are rare

1

type ____ curves are fairly common

2

type ___ curves are the most common

3

a cohort life table is calculated on the basis of a cohort of organisms

followed throughout life

a static life table is calculated on the basis of a cross section of a

population at a specific time

cohort life tables are

• most reliable life table

• records kept throughout life on number of individuals who are born about the same time

• difficult to collect data

• there are serious practical problems to overcome for studies of most populations

it is difficult to collect data for cohort life tables because

you must mark all the individuals, and you must follow each individual through its life and record the time of its death

Static life tables

• less reliable life table

• ages at death of individuals are recorded

• individuals are born at different times

• much easier to carry out for many populations

• age estimates are sometimes quite easily made for some types of organisms

Assumptions for static life table to correctly indicate cohort survival probabilities

• constant age distribution

• no year to year variation in total births

• no year to year variation in age-specific survival

if a population is increasing the older age classes will be

under represented in a static life table

if a population is declining then older age classes will be

over represented in a static life table

static life tables are

imperfect

Ecologists typically collect 3 types of data to construct life tables

1. survivorship directly observed

2. age at death observed

3. age structure directly observed

survivorship directly observed

directly generates a cohort life table

age at death observed

can be used to generate a static life table

age structure directly observed

can be used to generate a static life table

Standardized symbols used in life tables (Bx)

expected number of offspring for each female in cohort

a net reproductive rate holds for organisms with

non-overlapping generations

Standardized symbols used in life tables (R0)

number of female offspring produced in generation t+1 divided by the number of female offspring produced in generation t

what does an R0 of 3 mean

a population can triple its size with each generation

what does an R0 of > 1 mean

a population is growing geometrically

what does an R0 of 1 mean

a population is neither increasing nor decreasing with each generation

what does an R0 of < 1 mean

a population is decreasing with each generation

we can use age distributions to predict whether populations will

increase, decrease, or stay constant

Intrinsic capacity for increase ( r )

this is one way to combine morality and reproduction for organisms with overlapping generations

r is also known as

biotic potential

intrinsic capacity for increase in numbers ( r ) was first derived by Lotika in

1925

r depends on fertility, longevity, and speed of development measured under

idealized conditions

R is most commonly measured as the difference between

natality rate and death rate under ideal conditions

geometric/exponential growth is a basic and extremely important concept in ecology it is commonly called

one of the fundamental “laws” of ecology

population growth cannot go on forever

there needs to be population regulation

if (___) is positive then there is exponential growth

r

when multiplication rate is independent of population size, population increase is given by

dN/dt = rN

when multiplication rate is dependent of population size,

as density rises the presence of more and more individuals will start to reduce longevity and fertility of other individuals due to shortages in resources, causing a reduction in growth rate

K =

carrying capacity of environment

when growth is reduced by increasing N, the result curve of N against time is

S-Shaped

dN/dt = rN((K-N)/K) what does (N) stand for

population size

dN/dt = rN((K-N)/K) what does (t) stand for

time

dN/dt = rN((K-N)/K) what does (r) stand for

intrinsic capacity for increase

dN/dt = rN((K-N)/K) what does (K) stand for

upper asymptote or maximum value of N (carrying capacity)

a logistic curve has two attractive attributes

it is simple and its symbols can be given biological meaning

carrying capacity

what is the maximum population size that can be supported by the resources available

the realized population per capita growth rate is defined as

dN/dtN

with exponential growth, r equals

dN/dtN

when growth is not exponential the intrinsic capacity for increase is not the same as the

realized per capita growth rate

r can be considered a constant for

a particular population and is always positive

dN/dtN can be negative when

a population is declining

dN/dtN becomes positive when

the population is growing

dN/dtN is what is measured in real populations and will only be the same as r during those times that

the focal populations is growing exponentially

growth is not continuous in

field populations

species with ______-lived individuals that have low reproductive rates are typically more stable than species with ______-lived individuals and high reproductive rates

long; short

small, short lived populations are generally more vulnerable to

environmental changes

densities of populations that depend on limited resources fluctuate in ___________ ________ more than those that use a greater variety of resources

population size

episodic reproduction generates

fluctuation

the total number of births and the growth rates of individuals tend to be highest when a population is

well below its carrying capacity

populations with high reproductive capacity can sustain

their growth despite a high rate of harvest

to reduce the size of populations of undesirable species

removal of resources is more effective than large-scale killing

by removing resources, species will have reduced

carrying capacities and therefore lower numbers

killing in large numbers of species would reduce them to a population size that grows

more rapidly to reach its carrying capacity

if a rare species is to be preserved, the most important step is

to provide it with a suitable habitat

the difference between the real world data and made up studies is

the consistency, real world studies will fluctuate and not be uniform in any way

varmints

anything considered a pest

Interactions can be defined based on

their effects or they can be defined based on their underlying mechanism

Direct interaction

individuals physically interact (negative for both)

indirect interaction

individuals affect each other negatively but not physically (ex. herbivores compete for resources but don’t physically fight)

competition

two species use the same limited resource to the detriment of both

predation

one animal species eats all or part of another animal species

herbivory

one animal species eats all or part of another plant species

parasitism

two species live in a close association in which the parasite depends metabolically on the host

Disease

an association between a pathogenic microorganism and a host species in which the host suffers physiologically

mutualism

two species live in close association with one another to the benefit of both

resource/scramble/exploitative competition (indirect competition)

when a number of organisms utilize common resources that are in short supply

interference/contest competition

when the organisms seeking a resource harm one another in the process, even if resource is in short supply

INTRAspecific competition

competition between members of the same species

INTERspecific competition

competition between members of different species

conversions allow

two competition factors to be compared using alpha and beta conversion factors

when dN/dt = zero

we have no population growth/population reached equilibrium

a line on a phase diagram represents

a set of paired values (also represents where there is no population growth)