E4

Question 1

How much can populations grow?

Answer 1

No pop can grow forever, the limits imposed by finite plant restrict what otherwise appears to be universal feature of all species : a capacity for rapid population growth. Ecologists try to understand the factors that limit or promote population growth. In order to conserve endangered species, control pest species etc

Question 2

What are life tables?

Answer 2

Information about births and deaths, this is essential to predict trends or future population size. Life tables show how survival and reproductive rates vary with age, size, or life cycle stage.

Question 3

What is a cohort life table?

Answer 3

Follows the fate of a group of individuals all born at the same time. For organisms that are highly mobile or have long life spans, it is hard to observe the fate of individuals from birth to death.

Question 4

What is a static life table?

Answer 4

Survival and reproduction of individuals of different ages during a single time period are recorded, requires estimating age of individuals.

Question 5

Why are survivorship curves important?

Answer 5

For some species, age is important because birth and death rates differ greatly between individuals of different ages. In other species, age is not important. For plants, reproduction is more dependent on size. Life tables can also be based on size or life cycle stage.

Question 6

What are survivorship curves? And what types are there?

Answer 6

A plot of the number of individuals from a hypothetical cohort that will survive to reached different ages.

Question 7

What types of survivorship curves are there?

Answer 7

Type 1 - most individuals survive to old age
Type 2 - the chance of surviving remains constant through lifetime
Type 3 - individuals die at high rates when young, those that reach adulthood survive well.

Question 8

In what ways can survivorship curves vary?

Answer 8

Among populations of a species, gender, among cohorts which experience diff environmental conditions.

Question 9

What can a population be characterised by?

Answer 9

It’s age structure which influences whether a population will increase or decrease in size. Life table data can be used to predict age structure and population size.

Question 10

How do you predict population size?

Answer 10

Number of individuals that will survive to the next time period, number of newborns those survivors will produce in the next time period.

Question 11

What is growth rate calculated as?

Answer 11

Ratio of the population size in year t + 1 (Nt+1) to the population size in year t(Nt)

Question 12

When what factors are constant do pops grow at fixed rate

Answer 12

Age-specific survival and fecundity rates are constant overtime. Stable age distribution. If survival and fecundity rates change, we would obtain different values for the population growth rate and the stable age distribution

Question 13

What factors if effected can change be the population growth rate?

Answer 13

Any factor that changes Survival and fecundity of individuals. Ecologists and managers try to identify age-specific birth and death rates that most strongly influence population growth. This can be used to develop management practices to decrease pest populations or increase an endangered population.

Question 14

How have threats to loggerhead turtles been dealt with?

Answer 14

Focus on egg and hatchling stages, approach tested using life tables. Pop growth rate was most responsive to decreased mortality of older juveniles and adults through turtle excluder devices installed in shrimp nets.

Question 15

When can population growth rate be exponential?

Answer 15

When conditions are favourable, but exponential growth cannot continue indefinitely. In general, populations can grow rapidly whenever individuals leave an average of more than one offspring over substantial periods of time. If pops reproduce in synchrony at regular time intervals and growth rate remains the same. Geometric growth occurs.

Question 16

What is geometric growth and how is it calculated?

Answer 16

The population increases by a constant proportion, so number of individuals added to the population becomes larger within each time period. Frequency symbol = geometric growth rate ; also known as the per capita finite rate of increase. Nt = population at t generations, N0 = initial population size. Nt = frequency symbol t N0, Nt+1 = frequency symbol Nt

Question 17

What is exponential growth?

Answer 17

When populations increase by constant proportion. In many species, individuals do not reproduce in synchrony at discrete time periods, they reproduce continuously, and generations can overlap.

Question 18

How can you calculate exponential growth?

Answer 18

Exponential growth : dN/dt = rate of change of population size at each instant in time, r = exponential growth rate or the intrinsic rate of increase. dN/dt = rN. N (t) predicts the size of an exponentially growing population at any time. N(t) = N (0) e rt

Question 19

Why do geometric and exponential growth curves overlap?

Answer 19

Because the equations are similar in form. If a population is growing geometrically or exponentially, a plot of the natural logarithm of population size versus time will result in a straight line.

Question 20

What geometric growth rates cause population changes and what changes do they cause?

Answer 20

When geometric growth rate is = 1 or r = 0, pop stays the same
When geometric growth rate is < 1 or < 0, pop decreases
When geometric growth rate is > 1 or > 0 pop growth geometrically or exponentially

Question 21

How can growth rate be estimated?

Answer 21

Life table data can be used to predict future population size, plot predicted population size versus time, and estimate growth rate from the graph. The doubling time (td) of a population is the amount of time it will take the population to double in size. td = In (2) /r

Question 22

What is net reproductive rate?

Answer 22

Mean number of offspring produced by an individual during its life time. Xfirst = age of first reproduction, Xlast = age of last reproduction. Whenever R0 > 1, geometric growth will be greater than 1. Under these conditions, populations have the potential to increase greatly in size.

Question 23

What factors cause geometric growth rate to fluctuate?

Answer 23

Density dependent and density independent factors.

Question 24

What are density dependent factors?

Answer 24

Temp, precipitation, catastrophes, floods or hurricanes. Insect populations size fluctuation is correlated with temp and average rainfall. These factors can cause birth, death, and dispersal rates to change. As densities increase, death rates increase, dispersal from the population increases, all of which tend to decrease population size.

Question 25

When does population regulation occur?

Answer 25

When density dependent factors cause populations to increase when density is low, and decrease when density is high. Ultimately, food, space, or other essential resources are in short supply and population size decreases. Regulation refers to the effects of factors that tend to increase geometric rate or r when the pop size is small and decrease geometric rate or r when pop size is large. Density independent factors can have large effects on pop size, but they do not regulate pop size.

Question 26

How has density dependence been documented in natural populations?

Answer 26

In song sparrows, the number of eggs laid per female decreased with density, as did the number of young that survived. Unless a food source was supplied.

Question 27

How has density dependent mortality been observed in many populations?

Answer 27

Yoda et al, planted soybeans at various densities, at the highest planting densities, many of the seedlings had died by 93 days of age. When birth, death, dispersal rates show strong density dependence, populations growth rates may decline as densities increase.

Question 28

What is logistic growth?

Answer 28

Populations increase rapidly at first, then stabilises at the carrying capacity. Growth rate decreases as the population size nears carrying capacity because resources such as food, water, or space begin to run short. At carrying capacity, growth rate is zero.

Question 29

What is the logistic equation?

Answer 29

dN/dt = rN (1 - N/K). In exponential growth equation r is assumed to be constant. To make it more realistic we assume that r declines in a straight line as density (N) increases.

Question 30

What is logistic growth similar to at low density?

Answer 30

Exponential growth. When N is small close to 1, and a population with logistic growth increases at rate close to r. As density increases growth rate approaches 0. If conditions increase pop could increase beyond the predicted carrying capacity. If pop is growing exponentially, plotting the natural log of population size versus time will result in a straight line.