Unit 3 - Chapter 1 - Population Characteristics Flashcards
- What is a Population?
- ## POPULATION STRUCTURES:
5 attribtues that describe a population
- refers to a group of individuals of the same species that inhabit a specific geographic area and interact with one another at the same time. (These individuals have the potential to interbreed and produce fertile offspring) —characteristics include size, density, distribution, genetic composition.
1. ABUNDANCE (the size) : total # of individals in a population. Influences competition, resource availability, genetic diversity, body size (increase body size, decrease abundance/density due to resource competition). Populations can increase or decrease. Abundance is a fxn of pop. size & range over which the pop. is distributed.
2a) CRUDE DENSITY : # of individuals per unit area or volume. How crowded are individuals? Influences competition for resources and low density can affect mating opportunities or social interactions. Limitations = if individuals are not evenly dispersed throughout, calculations limited by # of measurements are taken and how close to the mean of the population.
2b) CRUDE DENSITY: can also find the ecological density by measuring the # of individuals per unit of distance, in the living space (could be along a linear ditch or rows between farmfields. Limitations: does the scientist know where to find the species?
3. AGE DISTRIBUTION : proportion of individuals in different age classes. Provides insight into reproductive potential, survival rates, population dynamics. Age classes include: Juveniles, Sub-Adults, Adults.
a) Non-Overlapping Generations : no age structure because individuals reproduce and die in a single season (ex: Mayflies)
b) Overlapping Generations: has all age classes
To gather data on ages, need THEIR AGES:
1. Direct Observation - organisms with clear external morphological changes during development (insects, amphibians) and can see specific characteristics
2. Growth rings or annuli - trees or bivalve mollusks, can count rings or annuli that determine age because they are visible.
3. Marking/Recapture - mark when young and tracking subsequent growth and survival. Limitations: time-consuming, long-term commitment, resource heavy, mortality rates could be higher among tagged individuals, adequate sample size and ensuring it represents the population.
4. Sampling Dead individuals: but again, the limitations include the deceased individuals not being uniformly distributed or easily detectable, maybe too decomposed, only captures a snapshot of the age of that particular individual - not of the whole population, may not even find all the deceased individuals so this leads to missing data that affects accuracy of the age structure estimation.
4. SEX RATIO : proportion of males to females. # of males per 100 females. Deviations from an equal-sex ratio can have implications for mating patterns, reproductive success, & population growth.
5. SPATIAL DISTRIBUTION : describes the arrangement/dispersion pattern of individuals within a population (clumped or dispersed) over an area or in a volume (aquatic). Not the same as geographic range, which includes the entire species. PATTERNS OF DISTRIBUTIONS: ‘ubiquitous species’ = a species across a very wide range, like song sparrows. Have larger population sizes due to larger geographic range. Influences interactions social interactions, resource availability, spread of diseases. ‘Endemic Species’ : species that are geographically restricted and have adapted to unique environmental conditions in that particular area, like golden lion tamarin (South Brazil). Vulnerable to habitat loss, environmental changes, disturbances to land. Smaller population sizes, due to smaller geographic range (less abundance).
Limitations (or assumptions): a)populaton could be migrating. b)the spatial scale. c)time of year. d)extrapolation & interpolation data - these distribution maps often assume that species distributions are continuous and predictable across the land. But the dispersal abilities will affect the distribution because species may not be equally living in all areas.
6. DISPERSION : 3 PATTERNS OF DISPERSAL (depends on spatial scale):
A) CLUMPED (aggregated): clustering together in groups or patches within a population. Commonly observed in species with social behaviours that are attracted by the resources or habitat. Contributing factors are availability of food, nesting sites, social structures (resources also clumped). Gives extra protection from predators, improved foraging, enhanced mating opportunities
B) RANDOM : individuals are distributed unpredictably and without any particular pattern within a population. Often observed in species with high mobility or when resources are evenly distributed - no need to have strong social or strong territorial behaviours.
C) UNIFORM : individuals being evenly spaced throughout a population. This pattern is typically observed in species that exhibit territorial behavior or intense competition for resources. Actively maintain a relatively equal distance from one another and defending their own territory.
7. SPECIES DETECTABILITY : ability to find or detect a species in a given area – due to surveying methods, sampling, species behaviour. Limitations = biased or incomplete data, leading to inaccurate distribution maps.
literally, drop a pin on the map/circle area.
POPULATIONS:
What is meant by a meta-population?
META-POPULATION : group of spatially separated sub-populations of the same species, connected through occasional dispersal and gene flow. (developed by ecologists Richard Levins/Ilkka Hanski) Recognizes that populations of many species are not continuous and stable thoughout their entire geographic range, but rather exist as a mosaic of interconnected patches of habitat patches. These habitat patches can be isolated from one another due to barriers such as geographic distance, unsuitable habitats, or human activities.
POPULATIONS:
TYPES OF INDIVIDUALS:
What is a UNITARY organism?
What is MODULAR organism?
What is a CLONAL colony?
- UNITARY : Exists as an individual. Develops from a single fertilized egg and maintains a fixed/distinct body structure thoughout it’s life. (no reproducing by cloning or fragmentation) Also has determinate growth. Ex: humans, dogs, frogs, whales.
- MODULAR : an organism that reproduces asexually through fragmentation or cloning. Has genetically identical ‘modules’ (zygote develops into modules) that separates from the parents and develop into new individuals. Ex: corals, Cavendish bananas.
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CLONAL COLONY : aka. ‘genet’ (individuals : ‘ramets’) Group of individuals that arise from a single parent through asexual reproduction. Offspring genetically identical due to same original parent. Ramets often share underground root system. Ex: Quaking Aspens
NOTE: if talking about it genetically, then yes, it’s an ‘individual’. If talking about productivity, then it’s multiple trunks of trees that are individuals.
How to count a clonal colony, for population count?
* Area-based Estimation: measure total area covered by clonal colony. then estimate the density of ramets within a representative portion of the colony
From 2a and 2b above (DENSITY)-
POPULATION STRUCTURE:
What are 2 methods for estimating population density? Organisms applied to? Limitations?
From the ‘Praire Ecologist’:
“Habitat heterogeneity simply means diversity or variety in habitat types. Habitat homogeneity is the opposite – a lot of habitat that is all the same” (see picture)
POPULATION DENSITY :
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LINE TRANSECT METHOD : placing a straight line across a habitat and recording the # of individuals or signs of their presence that intersect that line. Application: organisms that are relatively immobile or have clearly defined territories. Limitations:
a) Detection Bias (assumes all individuals are detected equally on this line, but some may be camougaged or there might be observer error)
b) Varations in Density ( assumes a constant density of individuals across the entire habitat - is it random or clumped dispersal? This is why replicates are needed.)
c) Habitat Heterogeneity (individuals are not uniformly distributed in the habitat - there are other organisms in the habitat)
Ex: plants, sessile organisms, terrestrial animals.
1b). QUADRATS : a square that is randomly placed in a habitat, of a specific size, count the individuals. Then replicate it. Due to known-size, it’s individuals/size of area (or volume in aquatic areas). Application : sessile organisms like plants, fungi, cnidarians (coral reefs). Limitations: see above
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MARK-RECAPTURE METHOD: capturing a sample of individuals, marking them (tags, bands, paint) then releasing them back into the population. Then recapturing them at a later time. Application : mobile organisms, move freely within habitat. Limitations :
a) Assumption of equal catchability (not all individuals have the same probability of being captured. Could be because they become ‘trap-happy’ and don’t mind going in the trap and others may become very skittish and completely avoid the trap.
b) Mark loss or Mortaility of organism (tag retention, higher predation that is naturally occurring or because the tag is causing more predatio, human disturbance)
c) Closed Population (assumes that the population is closed - no new individuals added or lost by births, deaths, immigration, emigration during the sampling period)
Ex: birds, mammals, fish.
**POPULATIONS & AGE STRUCTURE **(#3 from above)
What do the shapes of the Age Pyramids tell us about the GROWTH of the population?
pyramids can be made from SIZE or DEVELOPMENTAL STAGES.
- 1st one: replacing themselves with juvenile
- 2nd one: lowered replacement
- 3rd one: decreasing population, not replacing themselves.
What is meant by DISPERSAL?
Sinks & Sources in patches?
- movement of individuals from their birth or original location to another, new location (flying, walking, swimming, drifting with wind or water currents)
- Plays a crucial role in shaping the distribution, genetic diversity, & dynamic of populations/communities.
EMIGRATION : leaving or moving away from a particular population/habitat. Due to resource availability, competition, environmental changes, dispersal behaviour.
IMMIGRATION : movement into a specific population or habitat from other areas. Contributes to population growth, genetic exchange, introduction of new traits, genetic diversity.
MIGRATION : regular movement of individuals between habitats, often seasonal, in response to environmental cues or resource availability, such as mating opportunities, climate changes, need to use different resources in different seasons. Round-trip movement, returning to original habitat. Could be daily OR seasonal. Ex: birds, whales, fish.
WITH META-POPULATIONS - with subpopulations being interconnected:
a) Sink: high rate of mortality + lower quality of resources + lower birth rate. Despite receiving individuals through immigration, the local population within the patch is unable to sustain itself over the long term (net immigration into a patch). Sink patches rely on constant immigration to persist and would decline or go extinct.
b) Source: high reproductive rate + high quality resources + lower mortality rate. Source patches have a self-sustaining local population that produces a surplus of individuals that can disperse and colonize other patches (net emigration from the patch). These patches act as sources of individuals that contribute to the colonization and population growth of neighboring patches.
Lifetime Dispersal Distance : can determine the spread of a species, important metric for studying the spread of invasive species.
What is an Invasive Species?
The term “invasive species” generally refers to non-native organisms that possess the ability to rapidly spread and have significant potential to cause economic and environmental harm, leading to a loss of biodiversity and disturbances in local ecosystems. These species often display ecologically dominant characteristics that can result in the extinction of native species (Lymbery, 2017).
- Also useful for determining the vulnerability of a group to climate change
- European Starlings
- Giant Hogweed
- Zebra mussells
TEST: Describe the attributes of this population (look at the 1st big slide!)
5 ATTRIBUTES OF THE DISTRIBUTION MAP BELOW:
- DISTRIBUTION: drop the a mark on the map, finish up, draw a big circle around all the dots. Area this sample is found. (Remember, discussing the ‘species’ is when you say ‘geographic range’)
- DISPERSION PATTERN : clumped, with large spaces between individuals.
- DISPERSAL : not the same as dispersion pattern. Net immigration + net emigration– so for this sample, it is a SOURCE because there are more dots moving out.
- GEOGRAPHIC RANGE:nopers, only for the whole of the species!
- ABUNDANCE: total # of individuals in this sample. Count the dots.
- DENSITY: # of individuals per unit area (or volume for aquatic). choose 3 or 6 squares. Add up dots, divide by area. So 18/6 m^2= 3 individuals on average per square. THEN, 7x7=49 squares the dots cover. so finally, 49 m^2 x 3 individuals per m^2 = 147 individuals in this sample.
