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Ecology > Lec 8-10 > Flashcards

Lec 8-10 Flashcards

1
Q

What do population ecologists study?

A

1) Dispersion
- -How are individuals spread out within the population

2) Abundance (size and density)
- -How many individuals are there in the population, and how many individuals are there per unit area?

3) Growth
- -Is the size of the population changing (growing/declining) over time?
- -Positive or negative growth

4) Age/stage/size structure
- -How many individuals of different ages/stages of development /size are there in the population?

5) Sex structure
- -How many males and females are there in the population?

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2
Q

Population Dispersion Patterns

A

Three ways individuals can be spread out in a population:

1) Random
2) Clumped (AKA aggregated)
3) Regular (AKA uniform)

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3
Q

Random Dispersion

A

Null, starting point

The expected dispersion pattern in the absence of any biological interactions
–There are almost always biological interactions, which makes this unlikely

Very RARE

An example may be some tree species within tropical rainforests

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4
Q

Clumped Dispersion

A

The MOST COMMON dispersion pattern

Can result from :

  • Favorable habitat patches (if the resources are clumped, the organisms will be too)
  • Reproduction and other social behaviors (mammals and insects)
  • Defense (schooling fishes)
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5
Q

Regular Dispersion

A

NOT as common as clumped, but much MORE common than random

Can result from:

  • Competition for resources (desert shrubs)
  • Territoriality (birds)
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6
Q

Desert shrubs

A

Not too close to avoid sharing nutrients, not too far to avoid wasting nutrients

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7
Q

Measuring population size

A

Complete counts of individual organisms in a population are usually difficult or impossible

Methods for estimating population sizes involve sampling from the population and extrapolating to the actual size

Sampling procedures differ for sessile and motile organisms

Sampling methods for sessile organisms (such as lants and intertidal invertebrates) most frequently involve plots and line transects

One common procedure employing plots is the AREA-BASED COUNTS METHOD

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8
Q

Area-Based Counts Method

A

The plots are sampling areas of a specified size and shape

As many plots as possible are placed at random throughout the entire population, and individuals are counted within each plot

Plot should be large enough to include at least 10 organisms (may not necessarily contain 10)

n greater than or equal to 30

Example:

1m x 1m (1m^2) square plots are used for small acorn barnacles

Five 1m^2 plots are placed in the intertidal, and the number of barnacles is counted in each plot

17, 25, 4, 23, and 11 are the numbers of barnacles found in the five plots

The average number of barnacles per square meter is:
(17+25+4+23+11)/5 = 16

If the intertidal area in which these small acorn barnacles live is 4,000m^2, the total number of barnacles in the population is estimated as:
16x4,000 = 64,000

Assumptions of the area-based counts method:

1) Individuals can be identified and counted accurately within each plot
2) The plots are representative of the entire population’s area (placed randomly and interspersed throughout the population)
3) The size of the population’s area is known

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9
Q

Sampling Methods for Motile Organisms (such as most animals)

A
  • Trapping
  • Spotting
  • Listening for vocalizations
  • Looking for evidence (burrows, nests, tracks, etc.)
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10
Q

One common procedure employing trapping is the _______________________

A

Mark-recapture method

Examples:

  • Pitfall trap
  • Sherman trap
  • Mist net
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11
Q

Mark-Recapture Method:

A

Trap (capture) indivuals from the population at time 1

Mark each captured individual (using a pen, tag, implanted chip, etc.)

Release the captured individuals

In a few days (time 2), trap (capture) individuals from the population again and record how many are marked (recaptured)

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12
Q

M =

A

captured and marked at time 1

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13
Q

N =

A

Total # of individuals in the population

This is what we solve for

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14
Q

R =

A

individuals recaptured at time 2

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15
Q

C =

A

Total # captured at time 2

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16
Q

M/N is ____________________ and R/C is _______________________

A

the proportion of individuals in the population that were marked at time 1; the proportion of marked (recaptured) individuals in the sample at time 2, which should estimate (be equal to ) M/N

R/C = M/N

Solve for N:
N = (MC)/R

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17
Q

Example of Mark-Recapture Method

A

Snowshoe hare population in Minnesota in 1933

M = 948 hares captured and marked at time 1

C = 421 hares captured at time 2

R = 167 hares recaptures (already marked) at time 2

N = ?

N = (MC)/R

N = (948x421)/167 = 2389.868

Minnesota’s snowshoe hare population in 1933 was estimated to consist of 2390 individuals
–Can’t have a fraction of a hare

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18
Q

Mark-Recapture Method Assumptions

A

1) Population size stays constant between times 1 and 2
- -Can’t do during baby or migration seasons
- -Can’t have a bunch of death

2) All individuals in the population have an equal chance of being captured
- -Same chance of capture at both times; capture doesn’t affect behaviors

3) Marking or capturing does not affect behavior
- -Same chance of capture at both times; capture doesn’t affect behaviors

4) Marks are not lost between times 1 and 2

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19
Q

Modeling Population Growth

A

The purpose of population models:

  • Abstract representation of populations
  • If a population matches the model, use the model to make predictions about the population into the future
  • If a population does NOT match the model, examine the population more closely to determine what is not accounted for by the model
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20
Q

Population growth Formula

A

N(t+1) = N(t) + B - D + I - E

N(t) = population size at current time period

N(t+1) = population size at the next time period

B = # births during time period

D = # deaths during time period

I = # immigrations into a population during time period

E = # emigrations out of a population during time period

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21
Q

Exponential Population Growth

A

During exponential growth, the number of individuals in the population will increase over time at an increasing rate

Represented by J-shaped growth curve

As you add more individuals into population, if increases at faster rate over time

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22
Q

Current Model of Exponential Growth for Continuously Breeding Populations:

A

(dN/dt) = rN

r > 0 => Population increasing (b > d)
r = 0 => Population stable (b = d)
r < 0 => Population decreasing (b < d)

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23
Q

Current Model of Exponential Growth for Discretely Breeding Populations:

A

N(t+1) = lambdaN(t)

lambda > 1 => Population increasing
lambda = 1 => Population stable
lambda < 1 => Population decreasing

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24
Q

Predictive Model of Exponential Growth for Discretely Breeding Populations:

A

N(t) = (lambda^t)N(0)

t = year you are trying to predict to 
--t = 0 => now; t = 1 => 1 year from now
25
Q

Predictive Model Exponential Growth for Continuously Breeding Populations:

A

N(t) = [e^(rt)]N(0)

26
Q

Current Model of Logistic Growth for Continuously Breeding Populations:

A

(dN/dt) = rN (1 - N/K)

Density dependent birth (b’) and death (d’) rates

b' = b - aN
d' = d + cN
27
Q

Assumptions of Exponential Growth Models:

A

1) Population is CLOSED (no I or E)
- -Will include I and E when considering metapopulations

2) No population structure (all individuals have the same b and d)
- - Will change b and d for different individuals when considering age, size, and stage structure

3) No resource limitation which keeps r and lambda the same forever
- -Will consider the effects of resource limitation with logistic growth models

28
Q

Does Exponential Growth Ever Occur?

A

It can occur, but usually does so for only a short period of time

Seen in populations experiencing particularly favorable conditions

  • Most often in introduced/invasive populations
  • Plenty of resources, little threats from predators or parasites
29
Q

What are the limitations on population size and exponential growth?

A

1) Density-independent factors

2) Density-dependent factors

30
Q

Density-independent factors:

A

Do NOT depend on density (size)

Have approximately the same effect on b and d in both small and large populations

Include chance events such as disturbances and environmental fluctuations such as climate change

31
Q

Density-dependent factors:

A

Depend on density (size)

Increase in effect as population size (N) increases

Include limited resources and diseases

32
Q

Logistic Population Growth

A

The logistic growth model is used to show density-dependent effects on population growth

During logistic growth, the number of individuals in the population will initially increase rapidly but will then stabilize at a constant size

  • -The growth rate becomes 0 (b = d)
  • -Initially looks like exponential growth, but then it levels off

Equation: dN/dt = rN (1 - (N/K))
–When N is small, the logistic equation is very similar to the exponential equation

As N approaches K, the entire term becomes zero, and the population size stops changing over time

33
Q

r-related species

A

r signifies that these populations are always in the beginning, exponential growth portion of the logistic curve

34
Q

K-selected species

A

K signifies that these populations are always near the carrying capacity of the logistic curve

35
Q

The previous models assumed that all individuals in a population have the same _____________

A

birth and death rates

36
Q

Factors that affect birth and death rates

A

1) Age
- -Very young individuals have birth rates of zero
- -Very old individuals have high death rates

2) Size
- -Smaller plants and animals have lower birth rates and higher death rates than larger individuals of the same age
- —Size is NOT the same as age

3) Stage of development
- -Dramatically different for insects
- -Seeds of some plants can live for hundreds of years without germinating
- –Stage is NOT the same as age
- -Juvenile birds can be as large as adults, but they have different birth and death rates
- –Stage is NOT the same as size

4) Sex
- -Death rates for males are higher than those for females in humans
- –This has not always been the case
- -Birth rate for males is zero

37
Q

Life tables

A

Show the number of individuals alive in a population over time, plus how survival and reproduction vary at these different times (ages, sizes, or stages)

38
Q

Life table parameters

A

x = time interval corresponding to age/size/stage

N(x) = # of individuals surviving to each age x

S(x) = age-specific survival rate - the probability that an individual age x will survive to age/size/stage x+1
–Calculated as N(x+1)/N(x)

l(x) = survivorship - the proportion of individuals that survive from birth (age 0) to age x
–Calculated as N(x)/N(0)

F(x) = Fecundity - the average # of offspring produced by individuals of age x
–Fecundity is NOT equal to fitness

39
Q

A cohort life table follows the fate of a group of individuals _______________________________________

A

All born at the same time (a cohort) until each has died

This is the MOST useful type of life table, but it can be challenging to construct

It is NOT always easy to find individuals from one time period to the next, plus it isn’t feasible for long-lived organisms

40
Q

Alternatively, a __________ can be constructed:

  • -The number of individuals of each age in a population is recorded during just a single time period
  • -Assumes that birth and death rates have remained constant since the oldest individual was born
A

Static life table

41
Q

Applications of life tables

A

1) Survivorship curves
2) Net reproductive rate
3) Life cycle graphs/diagrams and transition matrices

42
Q

Survivorship curve

A

Shows proportion of the total individuals that survive to each age (or size or stage)

It is constructed by plotting age on the x-axis against # of survivors (N(x)) on the y-axis (on a logarithmic scale)

3 types of survivorship curves commonly seen in nature

43
Q

3 types of survivorship curves

A

Type I

Type II

Type III

44
Q

Type I

A

Most individuals survive to old age, so mortality occurs late in the life history
–Typical of K-selected species

45
Q

Type III

A

Individuals die at high rates when young (most mortality occurs early in life), but those that reach adulthood persist
–Typical of r-selected species

46
Q

Type II

A

Chance of surviving or dying remains CONSTANT throughout the life history of the organism
–Species intermediate in the r-K continuum

47
Q

Net reproductive rate

A

(R(0)) represents the average # of offspring produced by individuals within a population throguhout their lifetimes

Multiply the survivorship by the fecundity for each age, then sum across all ages

R(0) = Sum (l(x)F(x))

48
Q

Life cycle graphs and transition matrices

A

Life cycle graphs display ages, survival rates from one age to the next (S(x)), and fecundities (F(x)) at each age

Transition matrices contain the same information, but can be used to predict the size of the population and its age structure into the future

49
Q

Stable age distribution

A

Total # of individuals, # individuals of each age, and lambda initially fluctuate considerably

After a few time periods, the proportion of individuals of each age, as well as lambda, will stabilize from one year to the next

Total # individuals will continue to increase or decrease over time

50
Q

Life cycle graphs and transition matrices are heavily utilized by ecologists and wildlife managers to:

A

Protect endangered species

Control invasive pest species

Determine sustainable harvest rates

51
Q

Protect endangered species

A

Loggerhead sea turtles are threatened by commercial fishing nets

Early conservation efforts focused on HATCHLING stage:

  • -Transition matric models showed that, even if hatching survival was increased to 100%, loggerhead sea turle populations continued to DECLINE
  • –Targeting efforts to HATCHLINGS would have little to no effect on population

Population growth rate predicted to be most responsive to decreasing the mortality of older adults

Turtle excluder devices now required in all commercial nets

ADULT mortality declined by ~50% since implementation of these devices, but will be decades before population response determined

52
Q

Metapopulation

A

Group of spatially isolated subpopulations that are linked together by dispersal (immigration or emigration) of individuals or their gametes

A single population that occupies a # of patches of suitable habitat

Most populations exist as metapopulations

53
Q

Local extinction

A

When all individuals in a subpopulation die or emigrate, so that subpopulation is gone

54
Q

Regional extinction

A

When all individuals in all of the subpopulations die, so that the entire metapopulation is gone

Risk of regional extinction much LOWER than risk of local extinction

55
Q

Persistence

A

In context of populations, opposite of extinction

Persistence of metapopulation (and therefore the overall population) occurs as long as at least one subpopulation persists

Persistence of the metapopulation is positively related to the # of subpopulations

56
Q

Very small subpopulations have a much ________ risk of local extinction

A

GREATER

57
Q

Allee effect

A

Population growth rate DECREASES as population size DECREASES

Due to individuals having difficulty encountering mates at low population densities

58
Q

Ecologists and wildlife managers focus their efforts on the _______ subpopulations

A

LARGER

A larger # of individuals leads to:

1) LESS chance of local extinction
2) A GREATER potential to disperse into other subpopulations
3) A GREATER potential to colonize favorable but unoccupied patches of habitat establishing new subpopulations

Ecology (13 decks)

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