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Life Science 142 > Ecology 3 - Populations > Flashcards

Ecology 3 - Populations Flashcards

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1
Q

What is a population

A

A population is a group of individuals of the
same species that occupies the same area

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2
Q

What is population ecology

A

Is concerned with fluctuations in population size and the factors that regulate populations

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3
Q

What is an open population

A
  • Movement of individuals freely between area
  • Can interbreed with any other individual

eg) human population

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4
Q

What is a closed population

A
  • Where indiviulas cannot go anywhere and interbreed with another individual
  • Can only interbreed with those in same sub-population
  • Some arent closed pop bc if fencing off but becauseorganism has restricted distribution which are very habitat dependent

eg ) 1. Elephants in kruger national park

  1. Bearded vulture ( resistricted to high mountains of the berg
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5
Q

What is demography

A
  • The statistical study of a
    population
  • Made up of the populations :
  1. Density
  2. Distribution
  3. Growth rate
  4. Mortality pattern
  5. Age distribution
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6
Q

Explain population density

A
  • Is the number of
    individuals per unit area or volume
  • Land = x ^2
  • If you know density you can scale up to population size if area is known
  • Marine = x^3 ( density )
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7
Q

Explain measuring population density

A
  1. Indirect indicators such as number of nests, burrows, droppings or tracks ( reduced cost and time )
  2. Direct measures = Usually impractical or impossible to count all individuals in a population – census ( count every organism in population )
  • eg. for whales or elephants in kruger national park using helicopters
  1. Sampling techniques
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8
Q

Explain sampling techniques

A
  • Take measurments from population and use them to come up with estimate of population size
  1. Sessile organisms = quadrant sampling

2.1 Mobile organisms = line transects ( corals; whales in Antartica )

2.2 Mark-recapture method
- Animals are captured and marked

  • After a time interval animals are captured again
  • A formula is used to calculate population size based on the ratio of marked and unmarked individuals
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9
Q

Explain population distribution

A
  • Is the pattern of dispersal of individuals

Determined by:

  1. Availability of resources, e.g. water, food, light
  2. Limiting factors – aspects of the environment that define the limits of where a certain organism can survive, e.g. temperature, oxygen concentration
  3. Behaviour (e.g. territoriality)
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10
Q

What are the patterns of distribution

A
  1. Unifrom
  2. Random
  3. Clumped
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11
Q

Explain uniform distribution

A
  • Is when the spacing of individuals is even
  • This may result from antagonistic interaction between individuals

For example, competition for a resource or social interactions that set up individual territories for feeding, breeding or nesting

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12
Q

Explain random distribution

A
  • Is when individual spacing varies in an unpredictable way
  • This occurs when individuals are neither attracting nor repelling each other and the environment is fairly uniform
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13
Q

Explain clumped distribution

A
  • Most common
  • Occurs when individuals aggregate in patches
  • This is the most common type of distribution
  • May result from:
  • Resources being concentrated in patches
  • Mating or other social behaviour
  • Lack of dispersal of young

eg ) whales; clumps of trees; school of fish

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14
Q

Explain distribution over time

A
  • Population distributions are not always static – they may vary over time
  • This may result from a change in weather conditions or in resource availability and abundance

For example, animals may aggregate only during the mating season

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15
Q

Explain population growth

A
  • Is the change in
    population size per unit time
  • The size of a population increases or decreases over time with a change in one or more of the following:
  1. Births (Natality)
  2. Deaths (Mortality)
  3. Immigration (Individuals join the population)
  4. Emigration (Individuals leave the population)
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16
Q

Explain populations growing and declining

A
  • Population growth can be positive, negative or stable
  • Populations grow when birth and immigration exceeds death and emigration
  • Populations decline when death and emigration exceeds birth and immigration
  • Populations remain stable when birth and immigration approximately equals death and emigration
17
Q

How is population growth calculated

A
  • Growth rate = [(Births + Immigration) –
    (Deaths + Emigration)] / Population size
  • Usually immigration and emigration are expected to cancel each other out and can thus be ignored, in which case the formula becomes:
  • Growth rate = (Births – Deaths) / Population size
18
Q

Explain population growth

A
  • Growth = Net reproduction per individual x Number of individuals

G=rN

19
Q

Explain biotic potential

A
  • Is the highest possible growth rate for a population when resources are unlimited

eg ) Dissolved oxygen, sunlight, water, carbon dioxide, mineral nutrients, organisms as food

20
Q

What does biotic potential depend on

A
  • Number of offspring per reproductive event
  • Chances of survival to reproductive age
  • How often an individual reproduces
  • Age at which reproduction begins

eg ) The four striped field mouse (Rhabdomys pumilio) mice has a higher biotic potential than the white rhinoceros (Ceratotherium simum)

21
Q

Explain mortality patterns

A
  1. Cohort = all the members of a population
    born at the same time
  2. Life tables follow the fate of a cohort
  3. Survivorship = the probability of a newborn in a cohort surviving to a certain age
  • Plotting the number of individuals still alive at each age produces a survivorship curve
22
Q

Explain life tables

A
  • Used to summarise patterns of life, death and reproduction in a population by following a cohort of individuals
  • They provide valuable information on population demographics
  • x = age interval (time units or
    stages)
  • nx = number alive at start of age x
  • dx = number dying between age x and x + 1 =nxt -nxt+1
  • qx = mortality rate between age x and x + 1 = dx/nx
  • mx = individual fecundity, or mean reproductive output, for each age class
23
Q

Explain survivorship curves

A
  • Is a graphic representation of the number of individuals in a population that can be expected to survive to any age
  • It is a plot of x and nx from a life table
  • Three types of survivorship curve are recognised
24
Q

Explain the types of survivorship curves

A
  1. Type I
    - Most individuals die later in life, e.g. large mammals
  2. Type II
    - Survivorship decreases at a constant rate over the life span, e.g. small mammals, songbirds
  3. Type III
    - Most individuals die early in life, e.g. invertebrates, fish
25
Q

Explain age distribution groups

A
  • Pre-reproductive
  • Reproductive
  • Post-reproductive
  • Depending on what proportion of the population falls into each of these groups, the population will have a particular age structure
26
Q

Explain age structure

A
  • Refers to the relative numbers of individuals of each age in a population
  • If the pre-reproductive age group is the largest, the population will increase; if it is the smallest, the population will decrease
27
Q

Explain population growth moving slowly or fast

A
  • Aopulation with more old, non-productive individuals will grow more slowly than a population with a larger percentage of young individuals of reproductive age
  • A shorter generation time (span of time between an individual’s birth and that of their offspring) results in faster population growth, assuming birth rate is greater than death rate
28
Q

What are the types of breeding population patterns depend on

A
  • Discrete (semelparity)
  • Continuous (iteroparity)
29
Q

Explain discrete breeding

A
  • Individuals have a single reproductive event in their lifetime
  • Non-overlapping generations

E.g. annual plants, univoltine insects (1 brood per year)

30
Q

Explain continuous breeding

A
  • Individuals have many reproductive events throughout their lifetime
  • Overlapping generations
  • Chance of survival is high

E.g. vertebrates, large plants

31
Q

Explain exponential growth

A
  • A population consisting of only a few individuals living in an environment with no limiting factors (i.e. no restrictions on available energy, growth, or reproduction) will increase over time in proportion to the birth and death rates
  • Usually occurs in organisms with discrete breeding
  • Growth accelerates over time indefinitely  Two phases:
  1. Lagphase–Growthisslowasthe population is still small
  2. Exponentialgrowthphase–Growth increases as more individuals are added

Life Science 142 (24 decks)

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