bio2129 topic 7
what is the defintion of population
all individuals of a given species
what is abundance
how many individuals of a species (or multiple species) are present in a given area or community
what is population density
number of individuals per unit space
what is the difference between abundance and population density
abundance = how many there are. density = how many there are relative to a space.
why is density is usually useful when comparing across habitats of different sizes.
if one habitat is bigger than another, it will naturally have more individuals, even if the organisms aren’t actually more common there.
what are the ways of measuring abundance in sessile organisms (none moving)
Quadrats, Transects
how do you use the Quadrats method
when you use a square sampling frame (quadrat) to count/estimate the number of organisms that don’t move (sessile) within that defined area.
what is the Transects method
a line/path along which you systematically record organisms or environmental data to count how abundance changes across space.
why are quadrats useful
can study spatial patterns (clumping/evenness), gives a standardized sample area to compare sites/habitats, good for sessile species
what are the main limitations of using quadrats and transects
there’s uncertainty and issues with spatial distribution that can affect how accurate or representative your data really is
what are the three distinctive patterns of spatial distribution of organisms
Random, regular and clumped
what is random spatial distrobution
individuals of a species are spread out unpredictably in an area
what is regular spatial distribution
individuals are spaced out uniformly throughout the environment
what is clumped spatial distrobution
individuals are found in groups separated by spaces where there are no individuals present
uniform spatial patterns have
low variance
random spatial patterns have
modterate variance
clumped spatial patterns have
high
what is an example of uniform spatial distrobution
tree plantations
what is an example of random spatial distribution
dandelions growing in a field, Each seed is carried by the wind and lands wherever it may. some land close, some far with no competition or attraction.
what is an example of clumped spatial distribution
herds, colonies
what did brisson and reynolds find out about the creosote roots, Larrea tridentata
They had competitive interactions with the neighbouring shrubs due to allelopathy (secretes chemicals in soil that reduces growth of nearing plants)
how to avoid catching the same moving organisms for sampling populations
Mark-release-recapture
what is MRR
once individuals are caught, they are marked/tagged/collared, then released
how does MRR work for sampling
Capture and mark M individuals.
Release them.
Later, capture n individuals and record m of them that are marked.
Estimate total population N with the Lincoln–Peterson index
what are some assumptions in MRR techniques
1) Individuals are equally capturable/detectable. 2) Population is stable during mark-recapture period. 3) Marked/unmarked individuals have the same chance of leaving through mortality/emigration. 4) Marks stay on organism
what is the lincoln-peterson index
a way ecologists estimate the total population size of mobile animals if you cannot count them individually
Community definition
interacting species inhabiting a defined area
Guild definition
a group of different species that use the same type of resource in a similar way
what is community structure
describes the patterns and organization of species within that community (# of species, abundance diversity)
life form definition
combination of structure and growth dynamics (what it looks like and how it grows)
when we talk about species abundance patterns how does Preston’s Distribution of Commonness and Rarity come into play
Most communities have a few very common species and many rare ones. significant effort to capture rare/elusive species
Preston graphed the abundance of species in collections as
frequency distributions. Lognormal distributions, bell shaped cruves
why is Preston's lognormal distribution important
1) Helps understand structure & balance of communities. 2) suggests most communities are dominated by a few abundant species and others are rare. 3) used to calculate species diversity or modeling biodiversity patterns
what are the ways to measure species diversity
Alpha diversity, Beta diversity, Gamma diversity
what is alpha diversity
richness in a locality (specific area)
what is Beta diversity
the degree where regional species exceed local richness (beta=gamma/alpha)
what is gamma diversity
regional species richness= alpha x beta diversity
what are the two factors in classical species diversity metrics
species richness and species evenness
what is species richness
number of species in a community
what is species evenness
relative abundance of species
diversity is higher when
species richness and evenness is higher
what is Shannon-Wiener Index
accounts for the abundance and number of species
in a rank-abundance curve
shallower slope = greater evenness.
evenness can be calculated as a proportion between
0 and 1
how to measure beta and community similarity
jaccord's index