LECTURE 25 : Groups & Populations Flashcards
group def,types and reasons they form
multiple organisms of same or different species
occupying a common space
Ephemeral (temporary and may form for specific purposes or periods) or Consistent (relatively stable and endure over longer periods of time.)
Reasons they come tog
Social (Positive Grouping): In some cases, organisms come together in groups for social reasons. This is often seen in species that benefit from living in close proximity to others of their kind. For example, some animals may form social groups for protection, mating, or raising offspring. These groups are considered positive because they provide advantages to the individuals involved.
Indirect (Sharing Common Resource): Groups can also form indirectly when multiple organisms are attracted to a common resource, such as a food source or a suitable habitat. In these cases, the organisms might not interact directly with each other, but they share the resource that brings them together.
Accidental (Random Chance): Sometimes, groups can form purely by random chance. Organisms may come together without any specific purpose or benefit, but simply because they happen to be in the same place at the same time.
population def
Population: ‘A number of organisms of the same species in a defined geographical
area’
properties of population
Properties of populations include:
* number of individuals or population size
* area they occupy
* age structure
* sex ratio
reasons for groups to form
Social (Positive Grouping), organisms come together in groups for social reasons e.g. protection, mating, or raising offspring
Indirect (Sharing Common Resource): attracted to a common resource, such as a food source or a suitable habitat. the organisms might not interact directly with each other, but they share the resource that brings them together.
Accidental (Random Chance): form purely by random chance. Organisms may come together without any specific purpose or benefit, but simply because they happen to be in the same place at the same time.
importance of population
Populations are essential for:
* Ecology:
Distribution and abundance of individuals
Density
* Evolution:
Populations of organisms evolve, not individuals
Gene flow
Conservation and management
Invasive species
Defining threat status of taxa
Translocations and restoration
Variables that drive changes in population size:
- Birth
- Death
- Emigration (number leaving population)
- Immigration (number entering population)
- Growth (individual)
- Age at maturity
- Sex ratio
population growth rate
the change in numbers of individuals over time
Population growth in “closed” systems
Where there is no emigration or immigration, the population is
“closed”; e.g. isolated areas, islands, mountain tops
- Nt = number of individuals in the population at time t
Nt+1 = Nt + Births – Deaths
Number next year (t+1) = Number (N) this year (t) after accounting for changes in births and deaths
exponential growth
Exponential is geometric: a population’s per capita growth [each individual contributes the same number of offspring] remains the same
irrespective of pop size; thus populations grow faster as they get bigger
discrete : reproduction occurs periodically [something that happens at specific times, like birthdays or holidays. In this case, some populations only have babies during certain times of the year. ]
Continuous : reproduction occurs year-round [something is happening all the time, like the seconds on a clock ticking away. So, some populations can have babies all year round]
r = instantaneous growth rate [how fast a population can grow]
r> 0 : growth, r< 0 : decline
logistic growth model
Resource limited growth
* Population growth is often resource limited
(e.g. food, space, water, nesting sites…)
* Numbers cannot increase without bound
Growth exponential at low numbers= resources are abundant
Growth slows at higher numbers = resources become limited
Growth stops at carrying capacity (K)
estimating birthrates
Common methods:
- Histology of reproductive organs [This is like doing a kind of medical exam on the animals. Scientists look at the reproductive organs (the parts that help animals make babies) to see if they’re ready for making babies. If these organs look developed and ready, it suggests that the animals might be having babies soon]
- Capture/counting of fertilised gametes [Scientists might collect these cells and count them. If they find a lot of these cells, it could mean that there are many potential babies on the way]
- Counting of newly born individuals [counting how many baby animals have just been born. By keeping track of the number of newborns, scientists can estimate how many babies are born over time.]
Estimating death rates (mortality)
Common methods
- Tagging [For species that are easy to catch and tag (like fish or birds), scientists can attach small markers or tags to them. These tags help identify individuals. Later, when researchers find tagged animals that have died, they can use this information to estimate mortality rates.]
- Follow individuals (for
sessile organisms) [Sessile organisms are those that can’t move around much. Examples include trees, corals, or barnacles. Scientists can keep an eye on these organisms and check if any of them die. By counting the number of deaths, they can estimate how many are dying in a given area.]
- Probability based (for more
motile organisms) [it’s harder to track individual deaths. So scientists use probability-based methods. They might capture and mark a group of animals, then release them back into the wild. After some time, they capture another group, and by looking at how many marked animals are in the new group, they can estimate how many have died]
Population growth in “open” systems
If individuals move in and out of the populations then it
is “open” and migrants are likely
Nt+1 = Nt + Births – Deaths + immigrants - emigrants
Estimating demographic rates - migrants
Movement
Tagging and recapture
- Physical {physical markers or tags, like leg bands for birds or small plastic tags for fish, which help identify individuals in the field.}
- GPS {use Global Positioning System (GPS) technology to track the precise movements of animals.}
- Radio telemetry {attaching radio transmitters to animals. Researchers can then use radio receivers to track the animals’ movements}
- Acoustic {used underwater to monitor the movements of aquatic species, such as fish or marine mammals.}
Genetics: analyzing the DNA of individuals within a population to understand their relatedness, identify parentage, and sometimes track migration patterns.
tagging and recapturing
Tagging and recapture [capture individuals in the population, attach identifying tags or markers, and then release them back into the wild. Later, they recapture some of these individuals to see how many have tags.]
