Topic 4 Ecology: Population Ecology

Question 1

• N, the total number of individuals in a population

Answer 1

Size

Question 2

• The total number of individuals per area or volume occupied

Answer 2

Density

Question 3

• Describes how individuals in a population are distributed. The dispersion may be clumped, uniform, or random

Answer 3

Dispersion

Question 4

• The description of the abundance of individuals of each age. The shape of the age graph changes based on the reproductive rate

Answer 4

Age Structure

Question 5

• How mortality of individuals in a species varies during their lifetimes. Can be described using a curve which is further grouped into different types:

Answer 5

Survivorship Curves

Question 6

a. Type I
b. Type II
c. Type III

Answer 6

Types of Survivorship Curves

Question 7

• Most individuals survive to middle age but mortality increases quickly in old age. Humans have a type I survivorship curve

Answer 7

a. Type I

Question 8

• The probability of survival is generally constant and independent of age. Hydras have a type II survivorship curve

Answer 8

b. Type II

Question 9

• Most individuals die young, with few surviving to reproductive age and beyond. Oysters are an example. This type of survivorship is typical of species that produce free- swimming larvae. Most of the larvae die and only a few survive to become adults

Answer 9

c. Type III

Question 10

a. Biotic Potential
b. Carrying Capacity (K)
c. Limiting Factors
d. Growth rate or population
e. Growth rate of a population
f. Intrinsic Rate
g. Exponential Growth
h. Logistic Growth
I. Population Cycle

Answer 10

Types of Population Growth

Question 11

• The maximum growth rate of a population under ideal conditions (unlimited resources and no restrictions). The following factors contribute to the biotic potential of a species: age at reproductive maturity, clutch size (number of offspring produced at each reproduction), frequency of reproduction, reproductive lifetime, and the survivorship of offspring that reach reproductive maturity

Answer 11

a. Biotic Potential

Question 12

• The maximum number of individuals of a population that can be sustained by a habitat

Answer 12

b. Carrying Capacity (K)

Question 13

• Elements that prevent a population from reaching its full biotic potential. There are two categories:

Answer 13

c. Limiting Factors

Question 14

i. Density-dependent

ii. Density-independent

Answer 14

Types of Limiting Factors

Question 15

• The limiting effect becomes more intense as the population density increases. Competition for resources, the spread of disease, parasites, predation, and toxic effects of waste products are examples of density-dependent limiting factors. In some cases, reproductive behavior is abandoned when the population attains a high density

Answer 15

i. Density-dependent

Question 16

• The limiting effect’s intensity occurs independently of the density of the population. Examples include natural disasters or big temperature changes

Answer 16

ii. Density-independent

Question 17

• r = (births - deaths)/N = b - m

Answer 17

d. Growth rate or population

Question 18

• ∆N/∆t = rN = births - deaths = bN - mN

Answer 18

e. Growth rate of a population

Question 19

• When the reproductive rate (r) is at its maximum (biotic potential)

Answer 19

f. Intrinsic Rate

Question 20

• Occurs whenever the reproductive rate (r) is greater than zero. This creates a J-shaped curve. The maximum rate is actually constant in this model, but the population accumulates more new individuals per unit time when it is larger, thus it curves to be more steep over time. If resources are unlimited, populations exhibit exponential growth

Answer 20

g. Exponential Growth

Question 21

• Occurs when limiting factors restrict the size of the population to the carrying capacity of the habitat.
• The equation is:
  (delta N/delta t) = rN (K-N/K)
• Where K is the is carrying capacity, otherwise known as the maximum population size that a particular environment can sustain. When the population size increases, the growth rate decreases and reaches 0 when the population size reaches the carrying capacity. The curve is s-shaped. Note that ZPG (zero population growth) occurs when the birth and death rates are equal (r = 0). There are also technically more factors than just birth and death; immigration and emigration also affect population dynamics, but we mostly ignore that for the purpose of equations

Answer 21

h. Logistic Growth

Question 22

• Population size fluctuates in response to varying effects of limiting factors. When the population grows over carrying capacity, the population may then be limited to a size lower than the initial K due to the damage caused to the habitat. Thus, K may be lowered or the population may crash to extinction. There may be associations (not necessarily causes!) in cycle fluctuations between the population sizes of two animal species with predator/prey ecology. Predator/ prey ecology would show an out of sync but similar cycle, since one group is always responding with delay. This is because the decline of a predator allows the prey to recover.
• However, parasite/host ecology is in perfect sync because the parasite relies on the host directly for survival. When one thrives, so does the other in full sync. Parasites may be more or less numerous than the host

Answer 22

i. Population Cycle

Question 23

• Exponential and logistic growth patterns are associated with two kinds of life history:

Answer 23

Note

Question 24

• In this type of population, the members have low reproductive rates with longer maturation times, and their size is roughly constant at K (e.g., human population). The population levels out at the carrying capacity. Remember that carrying capacity is a density dependent factor. Growth curves are sigmoidal because the carrying capacity levels it off. Competition among individuals tends to be stronger and there is a limitation imposed by resources. Because of strong parental care, most organisms survive, and so K-selected species have a type I survivorship curve.

Answer 24

1. K-selected Population

Question 25

- These species have rapid exponential population growth. They have numerous offspring that are small and have fast maturation, so little parental care is needed (e.g., bacteria). They are generally found in rapidly changing environments affected by density independent factors. R- selected species are also characterized by opportunistic species (e.g., grasses, insects that quickly invade a habitat and reproduce). These species have growth curves that are exponential. The population densities are well below carrying capacity, so there is little competition faced. R-selected species have a type III survivorship curve

Answer 25

2. R-selected Population

Question 26

- Human population growth has been exponential since about 1000 years ago. This is enabled by: increase in food supply, reduction in disease, reduction in human wastes, and habitat expansion because of advancements allowing the inhabitance of previously uninhabitable places. The rate is still increasing, but it is slowing down.

Answer 26

Human Population Growth

Question 27

- Bacterial growth has four phases plotted as the logarithm of bacteria # vs time. The first phase, lag phase, is when bacteria are adapting to growth conditions. Individual bacteria are maturing but are not yet able to divide. The second phase, log phase (exponential phase), is the exponential growth of the population as it doubles with every time period (using log # produces a straight line here). The third phase, stationary phase, is when the growth rate equals the death rate due to growth-limiting factors. The fourth phase, death phase, is when bacteria die.

Answer 27

Bacterial Growth

Question 28

- The aggregate land and water area necessary to produce all the resources to sustain an individual/group of people and absorb all their wastes.

Answer 28

Ecological Footprint

Question 29

- This is the overall variety of different kinds of organisms in a community and consists of two components:

Answer 29

Species Diversity

Question 30

- Reflects the diversity of a community by describing the total number of different species present

Answer 30

Species Richness

Question 31

- Is the amount of individuals of each species

Answer 31

Relative Abundance

Question 32

- Species diversity is measured by the Shannon diversity index. The higher the value, the more diverse the community. Higher diversity communities are often more resistant to invasive species.

Answer 32

Shannon Diversity Index

Question 33

- Species richness generally declines along a latitudinal gradient from the tropics to the poles due to evolutionary history (tropics are “older”) and climate. In terrestrial communities, sunlight and precipitation correlate with diversity and can be measured via evapotranspiration. Evapotranspiration measures the evaporation of water from soil and plants and is a function of solar radiation, temperature, and water availability. Evapotranspiration is highest in hot areas with abundant rainfall - Species richness is directly related to a community’s geographic size, which is described with a species-area curve: increases in area leads to increases in the diversity of habitats, which leads to increases of species - Species richness on islands depends on island size and distance from mainland. Equilibrium is reached when new immigrations are balanced by extinctions

Answer 33

Community diversity is affected by biogeographic factors: