Population Dynamics

Question 1

What is population dynamics?

Answer 1

Populations are always changing

Population dynamics looks at changes in population characteristics

But why would we want to study how populations are changing?

Question 2

Why would we want to look at how populations are changing? (4)

Answer 2

Studying populations dynamics allows us to gather data to :

Predict future trends in the growth of populations

Assess health of species/ecosystems

Develop policies/plans of action to save species from extinction

Address the impact of growing populations

Question 3

Why Study How Populations Change???

example

Answer 3

For example:
mosquitoes transmit malaria, a disease that kills over one million people annually.

An understanding of mosquito populations and their growth could lead to effective measures to control them.

Question 4

Characteristics Of Populations

Answer 4

Ecologists use quantitative measurements to study, predict, and describe populations.

Quantitative measurements are those that can be measured or presented numerically.

Question 5

4 main chars of pops

Answer 5

They include 
population size
density
distribution
life history

Question 6

Population size (N)

Answer 6

the number of individuals of the same species living within a specific geographical area.

Question 7

Population density (Dp)

Answer 7

the number of individuals per unit of volume or area.

Question 8

Determining the population size or density of a large area is difficult. Techniques?

Answer 8

transect , quadrat , mark recapture

Question 9

Transect Sampling

Answer 9

Members of a population may be sampled along a long rectangular area or line known as a transect.

To sample a transect, the researcher walks its length, counting the species being monitored. Only individuals within a certain distance of the line are counted. For plants, the distance may be 1 m. For mobile organisms, such as birds and mammals, the distance may be 50 m.

Transects are useful when density is low, or when organisms are very large

Question 10

Quadrat Sampling

Answer 10

A quadrat is an area of a specific size used for sampling a population. Quadrats are used to sample populations that are sessile (immobile) or that move very little and are very dense.

Several sample sites are randomly chosen, and quadrats of a known size, such as 1 m2, are marked. Researchers count the number of individuals inside the boundary of each quadrat.

Question 11

Sampling Using Mark-Recapture

Answer 11

Some wildlife populations are sampled using mark-recapture, a method in which animals are temporarily trapped, marked with a tag or transmitter, and then released.

At a later date, the same traps are set again

Scientists then compare the proportion of marked to unmarked animals to give an estimate of the population size.

Mark-recapture is useful for highly mobile organisms like fish or birds

Question 12

Distribution

Answer 12

Populations are rarely distributed evenly throughout their habitat.

Environmental conditions and suitable niches will influence how the population is distributed through a specified area

Biologists have identified 3 main dispersion patterns

Question 13

Biologists have identified 3 main dispersion patterns

Answer 13

• uniform is even
• clumped is clumpy
• random is all over

Question 14

Clumped Distribution

Answer 14

Populations gather near resources, which tend to be distributed unevenly. This results in clumped distribution. For example, animals may gather near water sources, and plants tend to cluster where moisture, temperature, and soil conditions are optimal.
Some animals gather into groups for positive interactions, such as protection from predators or hunting efficiency.

Question 15

eg of clumped

Answer 15

For example:
Shorebirds and meerkats find safety in numbers.
Humpback whales work in groups to catch prey for food.

Question 16

Uniform Distribution

Answer 16

Uniform distribution occurs when resources are evenly distributed but scarce. This distribution pattern is a consequence of negative interactions (such as competition) between individuals. For example:

Question 17

eg uniform distrib

Answer 17

Wolverines behave territorially to defend the food and shelter they need for survival. Keeping other individuals out of the area results in a uniform distribution.

The black walnut tree uses a chemical poison to deter the growth of other plants. This ensures that the walnut tree does not have to compete for resources.

Question 18

Random Distribution

Answer 18

If resources are plentiful and evenly distributed in an area, populations exhibit random distribution.

In random distribution, interactions among individuals are neutral. Since resources are abundant and well distributed, there is no need for individuals to defend their share. Random distribution is rarely seen in nature.

Question 19

Distribution Patterns Are Fluid

Answer 19

The distribution patterns described are models that help ecologists describe populations.

In nature, populations are fluid and may exhibit more than one of these distribution patterns throughout a life cycle.

Question 20

Life Histories and Populations

Answer 20

A life history is the survivorship and reproductive patterns shown by individuals in a population.

Life histories are quantitative measures of vital statistics that determine the size of a population.

The two main quantitative factors that describe life history are fecundity and survivorship.

Question 21

Fecundity

Answer 21

The average number of offspring produced by females of a species over their lifetimes is called the fecundity of that population.

Some organisms have the potential to produce very large numbers of offspring in their lifetime (high fecundity)
Other organisms produce only a few offspring over the course of their lifetime (low fecundity)

Question 22

Fecundity & Parental Care

Answer 22

An animal that has high fecundity normally does little to care for their young.

An animal that has only a few offspring per year tends to be very overprotective of them.

Does this behaviour make sense? Explain!

Question 23

Species Survivorship

Answer 23

Survivorship is the percentage of individuals in a population that survive to a certain age.

Biologists recognize 3 general patterns in the survivorship of species (Type I, Type II, Type III)

Data about survivorship can be depicted graphically on a survivorship curve (survival of individuals over the lifespan of a species)

Question 24

There are four (natural) processes that cause changes in population size:

Answer 24

immigration: the movement of individuals into a population
emigration: the movement of individuals out of a population
birth (or natality)
death (or mortality)

Question 25

immigration

Answer 25

immigration: the movement of individuals into a population

Question 26

emigration

Answer 26

: the movement of individuals out of a population

Question 27

Measuring Population Change

Answer 27

For most species, immigration and emigration are roughly equal, so ecologists do not factor them into population change calculations. The focus is on births and deaths in a population. The change in population size can be expressed using the following word equation: Change in a population size (ΔN) during a time interval = the number of births (B) – the number of deaths (D) Expressed mathematically, the equation is: ΔN = B – D

Question 28

An ecologist is studying a population of painted turtles. If 78 new painted turtles were born and 12 turtles died, the change in population size is calculated as:

Answer 28

ΔN = B – D = 78 – 12 = 66 turtles The change in popul

Question 29

Population Change with Immigration and Emigration

Answer 29

``` When these factors must be considered, population change can be determined using the following equation: ΔN = change in population B = births D = deaths E = emigration I = immigration ``` ΔN = [B + I] – [D + E]

Question 30

An ecologist is studying the human population of Kanata Ontario. If 105 children were born, 28 individuals died, 43 individuals moved into Kanata as 32 individuals moved into Ottawa. Calculate the change in human population size

Answer 30

``` ΔN = [B + I] – [D + E] ΔN = [105 + 43] – [28 + 32] ΔN = [148] – [60] ΔN = + 88 ```

Question 31

Rate of Population Growth By studying a population’s growth rate, ecologists can better understand the dynamics of a population and make better population management decisions. Population growth rates can be calculated using the following equation:

Answer 31

``` gr = growth rate ΔN = change in population size at different points over time [N2 – N1] Δt = change in time ``` gr = ΔN/Δt

Question 32

The population of the Banff Springs snails was estimated to be 3800 in 1997. Two years later, the population was estimated to be about 1800. The growth rate was determined using the following calculations:

Answer 32

Change in population size, ΔN = N2 – N1 = 1800 – 3800 = –2000 snails = –2000 snails/2 years = –1000 snails/1 year

Question 33

Measuring Per Capita Growth Rate

Answer 33

Measuring growth rate does not take into consideration how the initial size of the population may affect population growth. To make these calculations more meaningful, it is important to express the change in population size as the rate of change per individual or per capita. Per capita growth rate (cgr) can be calculated using the following equation: cgr = per capita growth rate ΔN = change in number of individuals N = original number of individuals cgr = ΔN / N

Question 34

In Kanata, a town of 1000 people, there were 50 births, 30 deaths, and no immigration or emigration in 1 year. The per capita growth rate (cgr) for the population that year is calculated as follows:

Answer 34

cgr = ΔN / N = 1020 – 1000/1000 = 0.02 The per capita growth rate is 0.02 or 2 percent. In this town, the population is growing. If the per capita growth rate is negative (as shown in the Banff Springs snails example), the population would be declining.

Question 35

Geometric Growth | Population Growth In Unlimited Environments

Answer 35

staircase lookin Aka discrete growth A pattern of population growth where organisms reproduce at fixed intervals at a constant rate In the case of the harp seal death is constant throughout the year Births increase during breeding season, then decline throughout the remainder of the year until next breeding season Growth rate is a constant…can be determined by comparing population size of one year to the same time the previous year

Question 36

Geometric growth formula

Answer 36

N(t)= N(0)𝝺t can be rearranged to 𝝺 = N(t+1)/Nt ``` N0= initial population size t = time 𝝺 = geometric growth rate ```

Question 37

Geometric Growth : Example (Text P. 663) Each May, harp seals give birth on pack ice off the coast of Newfoundland. In a hypothetical scenario, an initial population of 2000 seals gives birth to 950 pups, and during the next 12 months, 150 seals die. (a) Assuming that the population is growing geometrically, what will the harp seal population be in two years? (b) Assuming the same geometric growth rate, calculate the population size after eight years.

Answer 37

Each May, harp seals give birth on pack ice off the coast of Newfoundland. In a hypothetical scenario, an initial population of 2000 seals gives birth to 950 pups, and during the next 12 months, 150 seals die. (a) Assuming that the population is growing geometrically, what will the harp seal population be in two years? (b) Assuming the same geometric growth rate, calculate the population size after eight years.

Question 38

Exponential Growth | Population Growth In Unlimited Environments

Answer 38

A population growing at its biotic potential grows exponentially. Populations experiencing exponential growth are often found in controlled laboratory conditions, where there is no predation and resources are unlimited. This type of growth results in a J-shaped growth curve.

Question 39

Exponential Growth | Population Growth In Unlimited Environments

Answer 39

Aka continuous growth A pattern of population growth where organisms reproduce continuously at a constant rate Growth is continuous because deaths and births occur all year round Example: Humans

Question 40

exp growth equations

Answer 40

``` dN/dt = rN dN/dt = inst. growth rate r = intrinsic growth rate N = population size ``` ``` td = 0.69/r td = doubling time r = intrinsic growth rate ```

Question 41

Exponential Growth : Example

Answer 41

A population of 2500 yeast cells in a culture tube is growing exponentially. If the intrinsic growth rate r is 0.030 per hour, calculate: (a) the initial instantaneous growth rate of the population (b) the time it will take for the population to double in size

Question 42

Exponential VS Geometric Growth

Answer 42

Populations that grow exponentially increase in numbers rapidly…resulting in a J-shaped curve Exponential growth curve is smooth (as a result of continuous reproduction) in contrast to geometric curve But the overall trend is the same in both cases

Question 43

Population Growth in Unlimited Environments

Answer 43

The calculations described previously provide information for populations under ideal conditions (unlimited resources and no predators). Under these conditions, each species has its highest possible per capita growth rate (cgr). This is called its biotic potential.

Question 44

Logistic Growth | Population Growth In Limited Environments

Answer 44

Populations do not naturally grow to their biotic potential because resources are limited. In nature, a population will go through the following phases: Initially, the population will experience a lag phase (slow growth) as it establishes itself in the environment. The lag phase is followed by a period of rapid growth as the resources in the environment are exploited. The population eventually reaches the carrying capacity of the local environment, and the birth rate and death rate are more or less the same. The carrying capacity is the maximum population size that the available resources can sustain.

Question 45

Logistic Growth | Population Growth In Limited Environments

Answer 45

This population shows a logistic growth pattern (S-curve or sigmoidal curve), where growth is limited by the carrying capacity of the environment

Question 46

Population Growth In Limited Environments

Answer 46

The green line running through the S-curve represents the carrying capacity of the environment. The carrying capacity can change from season to season or year to year.

Question 47

Logistic Growth Rate Population Growth In Limited Environments equation

Answer 47

dN/dt = rmaxN[(K-N)/K] ``` dN/dt = inst. growth rate rmax = maximum intrinsic growth rate K = carrying capacity N = population size at a given time ```

Question 48

Logistic Growth Rate | Population Growth In Limited Environments

Answer 48

A population is growing continuously. The carrying capacity of the environment is 1000 individuals and its maximum growth rate, rmax, is 0.50. Determine the population growth rates based on a population size of 20.

Question 49

Population Growth Models & Life History

Answer 49

Life history traits are genetically controlled, but organisms use life strategies to maximize the number of offspring that survive to a reproductive age. Ecologists classify life strategies as r-selected or k-selected.

Question 50

R-selected strategy

Answer 50

Species that have an r-selected strategy live close to their biotic potential (r). These organisms: have a short life span become sexually mature at a young age produce large broods of offspring (high fecundity) provide little or no parental care to their offspring Insects and annual plants are examples of organisms characterized by r-selected strategies. They take advantage of environmental conditions (for example, food, sunlight, warm temperatures) to reproduce quickly.

Question 51

K-selected strategy

Answer 51

Organisms with a K-selected strategy live close to the carrying capacity (K) of their habitats. These organisms: have a relatively long life span become sexually mature later in life produce few offspring per reproductive cycle provide a high level of parental care Mammals and birds are organisms characterized by K-selected strategies.

Question 52

r- and K-selected Strategies

Answer 52

Although organisms tend toward either an r-selected or K-selected strategy, most populations are somewhere between the two strategies. For example, the balsam fir is a large tree that can live for many years, yet it produces hundreds of gamete-bearing seeds in cones. Classifying a population’s life strategy as r-selected or K-selected requires comparison to another population. For example, a rabbit population could be described as being K-selected when compared to a population of mosquitoes. However, when a rabbit population is compared to a population of bears, rabbits are better described as being r-selected.

Question 53

r- and K-selected Strategies | eg

Answer 53

Ecologists use an understanding of life strategies to predict the success of a population in a particular habitat.

Question 54

Arapidopsis (small flowering plant related to cabbage and mustard) are plants that “live fast, reproduce quick and die young”. Does this plant likely use an r-selected strategy or k-selected strategy? Explain.

Answer 54

r

Question 55

Factors Affecting Natural Populations | Density-Independent

Answer 55

Abiotic | Eg. flood, forest fire,

Question 56

Factors Affecting Natural Populations | Density-Dependent

Answer 56

Biotic | Eg. competition (intra-specific, interspecific)

Question 57

Factors That Regulate Natural Populations Density-independent Factors

Answer 57

Many abiotic factors, such as weather, can cause a population to crash when they change dramatically. These factors are called density-independent factors since they affect population growth in the same way, regardless of population density.

Question 58

Density-Independent Factor - Temp

Answer 58

This graph shows changes in temperature (a density-independent factor) that result in a population crash The decline begins well before the population is halfway to its carrying capacity and well before density would inhibit its growth. This decline is thus density-independent.

Question 59

Density-Dependant Factors

Answer 59

A density-dependent factor is a biotic interaction (such as competition or predation) that varies in its effect on population growth, depending on the density of the populations involved. The ability of these factors to slow a population’s growth depends directly on the density of the population. These factors have their greatest effect on populations at or near carrying capacity.

Question 60

Density-Dependant Factor - Competition

Answer 60

Each tree in this forest will release hundreds, perhaps thousands, of seeds. Of these seeds, only a small percentage germinate into young trees due to fierce competition for resources

Question 61

Competition

Answer 61

Intraspecific competition occurs when members of the same population compete for limited resources. It occurs most when a population reaches carrying capacity. As a result of the competition, the birth rate decreases or the death rate increases, or both, and population growth slows.

Question 62

Intra-Specific Competition

Answer 62

The growth of the wood bison population in the Mackenzie Bison Sanctuary is regulated mainly by the availability of food, which in turn is influenced by abiotic factors.

Question 63

Inter-Specific Competition

Answer 63

Interspecific competition occurs when two or more populations compete for the same limited resources. Often, one species will out-compete and exclude another species from a habitat. This is called the competitive exclusion principle, which states that two species with overlapping niches cannot share the same habitat.

Question 64

Inter-Specific Competition eg

Answer 64

Garlic mustard is an invasive species that out-competes native species for resources.

Question 65

Competition

Answer 65

Interspecific competition is reduced if resource partitioning occurs, where competing species use different resources within a habitat. Each of these warblers occupies a slightly different ecological niche, foraging for insects in different parts of a spruce tree. As a result, interspecific competition is reduced.

Question 66

Predator-Prey Interactions

Answer 66

Producers and prey use defensive strategies against their consumers and predators. These interactions put selective pressure on both parties – the more successful consumers and predators drive the natural selection of the producers and prey. For example, the scarcity of a producer or prey will limit the growth of a consumer or predator. Additionally, a large population of a consumer or predator will limit the growth of producer and prey populations.

Question 67

Predator-Prey Interactions | & Population Cycles

Answer 67

Predator-prey interactions are one of many factors that can result in regular population cycles – alternating periods of larger and smaller population sizes. The figure below shows a model of sinusoidal growth, a typical predator-prey wave-like growth pattern that is caused by the density-dependent effect each population has on the other. A simplified graph of predator-prey population cycles, such as elks and wolves, is shown here. An increase in prey increases the resources that are available to predators (A), so the predator population increases (B). This leads to a reduction in the prey population (C), followed by a reduction in the predator population (D). The cycle repeats itself over time.

Question 68

Predator-Prey Interactions | and Population Cycles

Answer 68

Other predator-prey models exhibit density fluctuations that roughly mirror sinusoidal growth. In this figure, the growth pattern is less regular than the sinusoidal growth model but shows the same cycling of predator and prey populations. Stoats (Mustela ermine) (A) and lemmings (Dicrostonyx groenlandicus) (B) share a predator-prey relationship in arctic ecosystems. The predator-prey relationship between stoats and lemmings follows an oscillating pattern (C) that resembles a sinusoidal growth curve.

Question 69

Predator-Prey Interactions & Population Cycles

Answer 69

The Canada lynx-snowshoe hare interaction is well studied. This interaction shows that both the predator-prey relationship and resource availability contribute to a sinusoidal growth pattern.

Question 70

Defense Mechanisms

Answer 70

Many organisms have adaptations that help them avoid predators. These adaptations are called protective colouration, and include the following: camouflage mimicry body colouration

Question 71

Defense Mechanisms: Camouflage

Answer 71

The dead leaf butterfly has brown colouration and a veined pattern on its wings to camouflage itself from predators.

Question 72

Defense Mechanisms: Mimicry batesian

Answer 72

In Batesian mimicry, a harmless species mimics the colouration and pattern of another species that has a more effective defense strategy.

Question 73

Defense Mechanisms: Mimicry | mullerian

Answer 73

In Müllerian mimicry, a poisonous species will mimic the colouration and pattern of another poisonous species to provide additional protection against predators.

Question 74

Symbiosis

Answer 74

Close interactions between two species living in direct contact often result in symbiosis. Symbiosis has one organism (symbiont) which lives or feeds in or on another organism (host) There are three forms of symbiosis: parasitism mutualism commensalism

Question 75

Parisitism

Answer 75

In parasitism, a symbiont (the parasite) benefits from the relationship but the host is harmed. Parasites include viruses, insects, unicellular organisms, and some worms. Tapeworms are a type of parasite. They are transferred from livestock to humans when people eat infected and undercooked beef or pork.

Question 76

Mutualism

Answer 76

In mutualism, both partners in a symbiotic relationship benefit from the relationship. For example, the sea anemone and the hermit crab have a mutualistic relationship. The sea anemone uses its stinging tentacles to protect the hermit crab from predators. In return, the hermit crab provides detritus from its meals as a food source for the sea anemone.

Question 77

Commensalism

Answer 77

In commensalism, one partner benefits and the other partner neither benefits nor is harmed. Some ecologists say there are few cases of true commensalism in nature because they believe that both partners in symbiotic relationships are usually affected in some way. However, it is often difficult to determine how both organisms are affected.