Population dynamics Flashcards
Population density formula:
Dp = N / A
N = sum of
individuals in the quadrats
A = total
area of the quadrats
Estimating population size:
Use the population density of several quadrats.
Example: Density population of daisies in 4 different 1.00 m2 quadrats. The section of the field is 10 000 m2
Quadrat #1: 5
Quadrat #2: 3
Quadrat #3: 2
Quadrat #4: 1
Dp = N / A
= 5 +3 +2 +1 / (4 X 1.00 m2)
= 2. 75 daisies / m2
If the entire study area is similar to the sample area, this density can then be extrapolated to determine the population size
Estimated population size = Dp X total study area
= 2.75 daisies/ m2 X 10 000 m2
= 27 500 daisies
Mark recapture
Animals are recaptured, marked with a tag or other, released and then recaptured later.
Example: 20 sparrows are captured and marked and
released. One week later, 50 sparrows are captured, and 10 of these were the marked sparrows
Population size (N) = (number original marked) X ( total individuals in recapture)
(marked individuals in recapture)
= (20 X 50)/10
= 100
Population distribution
- Populations are rarely evenly distributed throughout their
habitat. - There are 3 distribution patterns for populations: Uniform, random, and clumped
Clumped distribution
- Organisms tend to clump around resources, such as a water source
- Also common among species in which individuals gather into groups for positive interactions
Uniform distribution
- Where resources are evenly distributed but scarce, population exhibit uniform distribution
- It is usually a consequence of competition between two individuals
Random distrubution
- If resources are plentiful and uniformly distributed across an area, populations exhibit random distribution
- There is no need for individuals to defend their share and interactions between individuals are neutral
- These conditions are rarely met
in nature
Distribution patterns are fluid
Example: moose may cluster in small groups near food in the winter, but randomly disperse in the summer
Fecundy
- The average number of offspring produced by a female member of a population over her lifetime
- This number varies greatly depending on the organism. Some organisms only reproduce once in the their lifetime, others will reproduce many times. Some organisms produce one baby at a time, others hundreds.
- Fecundity is also affected by the age at which an organism becomes sexually mature. The faster the animal sexually matures, the more offspring they can have
Survivorship
-The number or percentage of organisms that typically live to a given age in a given population
- To study this, ecologists study a large group of individuals born at the same time, called a cohort.
- They will monitor this group over its lifetime and record the age of death for each organism.
Type 1 survivorship
This pattern is a curve and shows a high rate of juvenile survival and individuals that live until sexual maturity and beyond
Example: Humans. They have a high parental care for their young and even though we produce
fewer young, we have a high level of survivorship
Type 2 survivorship
The risk of mortality is constant throughout an individual’s lifetime.
Example: birds
Type 3 suvivorship
Most individuals will die as juveniles and only a few members will live long enough to produce offspring, and only a small few will live to old age
Example: Oysters
Female oysters release many eggs into the water, many of which will not be fertilized, and if they do they will most likely be consumed by predators.
Measuring population
Δ N = (B + I ) – (D + E)
Δ N = population change
B= birth
I= immigration
D= death
E= emigration
Calculating population growth rate
gr = ΔN/Δt
gr= growth rate
ΔN = change in population size
Δt = change in time
Calculating per capita growth rate
cgr = Δ N/N
cgr = per capita growth
Δ N= change in the number of individuals
N= original number of individuals
Population growth in unlimited
environments
- Conditions: ideal, no predators and resources are unlimited
- Biotic potential: Species have the highest possible growth rate.
Determined by 5 factors
- The number of offspring per reproductive cycle
- The number of offspring that survive long enough to reproduce
- The age of maturity
- The number of times the individuals reproduce in a life span
- The life span of the individual
Exponential growth pattern
- A population growing at its biotic potential grows exponentially.
- There is a brief lag phase, followed by a steep increase in the growth curve
- A pattern of a population where organisms reproduce continuously at a constant rate
Carrying capacity
- Carrying capacity is not a static condition
- It can change from season to season as conditions change
- Over time the population size fluctuates around the carrying capacity of the habitat in a stable equilibrium
- Populations can crash if resources are depleted faster than they can replenish
Life strategies
- Life strategies are strategies employed by organisms that can be correlated to the type of environment in which the organism lives
- Organisms have to make trade-offs to maximize the number of offspring that survive
R and K species
Species that have an r-selected strategy live close to their biotic potential (r). In general, these organisms
- Have a short life span
- Become sexually mature at a young age
- Produce large broods of offspring
- Provide little or no parental care to their offspring
Example: insects. They reproduce quickly when resources are favourable, but die in large numbers at the end of the season
Organisms with a K-selected strategy live close to the carrying capacity (K) of their habitats. In general, these organisms:
- Have a relatively long life span
- Become sexually mature later in life
- Produce few offspring per reproduction cycle
- Provide a high level of reproductive care
Example: mammals
Density independent factors
An abiotic factors that affects population growth in the same way, regardless of population density.
Examples:
- Natural disaters
- Temp change
Density dependent factors
A biotic interaction that varies in its effect on population growth, depending on the density of the populations involved.
- Disease
- Predators
- Water
- Mating
Competition
Intraspecific competition: a situation in which
members of the same population complete for resources.
Interspecific competition:
A situations in which two or more populations compete for limited resources
Often one species will out-compete the other
Competitive exclusion principle: two species with overlapping niches cannot coexist, but if their niches are different they can live in the same area, but affecting their population
Population cycles
Alternating periods of large and small population sizes. A predator-prey relationship is one way that a population cycle can occur
Sinusoidal growth: a wavelike oscillating growth pattern that is typical of predator-prey interactions
Defence mechanisms
Protective coloration: adaptations that help individuals avoid predation; includes camouflage, mimicry, and body colouration used as a warning signal
Interactions between producers and consumers typically results in co-evolution.
Parisitism
a symbiotic relationship in which a symbiont lives off and harms the host
Example: is a caterpillar and parasitic wasp eggs.
Mutualism
A type of symbiotic relationship in which both species benefit from the relationship
Commensalism
A symbiotic relationship in which one partner benefits and the other partner neither benefits nor is harmed
Invasive species (introduced species)
- Invasive species are non-native species that relocate to an area and outcompete the native species for resources
- These species usually do not have predators in their new environment, so they reproduce in large numbers
Example: The zebra mussels in the Great Lakes are a thriving invasive species. These mussels out-complete the native species for food and habitat.
K-selected species
Humans are K-selected
- Have a small number of offspring
- Reproduce later in life
- Provide parental care
Factors that affect growth
Many advances in technology occurred in a relatively short period of time
1700s: humans were able to increase their food supply by improved agricultural methods and domestication of animals
Late 1800s to early 1900s: breakthroughs in medicine enabled peoplem to be successfully treated for once-fatal illnesses
Better shelter protected people from the weather
Improvements in the storage capacity of food helped people survive when food was less plentiful
Population pyramids
Triangle shape: predicts a future of explosive growth because a large portion of the population will their reproductive years at the same time. It also indicates a decreased average life span
Rectangular shape: population is not expanding and is stable
Inverted triangle: indicates a population in shrinking. There are a large number of individuals that are past their reproductive years and few individuals in or about to enter their reproductive years
Ecological footprint
It is the total amount of land needed to support one person
and it includes six major categories of demand:
1. Cropland
2. Grazing land
3. Fishing grounds
4. Forest land
5. Carbon absorption land
6. Building area
Managing growth and resources
Like all populations, humans obtains the necessities for survival from their environment. Unlike other species, for many human their environment is the entire globe. The explosive growth of the human population has created some problems such as:
- Mercury contamination (toxicity and biomagnification)
- Deforestation
- Overharvesting Fish
- Marine Garbage
- Limiting biodiversity
- Overexploitation
- Invasive species
