8: Density, Distribution, Age

define population

group of interbreeding organisms of the same species

intraspecific interactions vs. interspecific interactions

intraspecific→interactions among individuals of same species

interspecific→interactions among individuals of different species

genet

sexually produced individual arising from single zygote

-includes subunits & they all grow from a single seed

ramet

ex?

asexually produced individual arising from the original genet & is genetically identical to that genet

(all ramets are one individual genetically)

ex// creosote bush

questions or problems with ramet?

when does individual die? what’s its life span?

define population density

number of individuals per unit of area

examples of linear density?

shores and beaches

basic methods for estimating density?

1) direct count

2) sampling

3) index

direct count method for estimating density?

-problem with this?

number of individuals recorded within an area of known size

-problem: difficult to do & not accurate

sampling method for estimating density?

number of individuals recorded within a small area, then extrapolated to a larger area

index method for estimating density

examples?

counting of objects related in some numerical way to animal’s abundance

ex// tracks, feces, roadkills

Relative abundance survey technique?

species may be ranked according to number of detections

ex// abundant, common, rare

mark-recapture survey technique

individuals in an area are captured & marked

what is the spot mapping survey technique?

-problem with this?

plotting locations of individuals on maps

-number of clusters=number of territories

-2 individuals(mated pair) per territory

problem: assumes species are territorial with monogamous mating system & no non-territorial individuals

What is the capture rate survey technique?

individuals are captured with like traps/nets and per unit of time is recorded

quadrats counting

-problem with this?

individuals are counted within a square or rectangle

-cannot be done on moving organisms

transect counting

individuals are counted while moving along a line

-length of line should be measured

-individuals can be counted on foot, plane, boat, etc

line transects without distance estimates

-issue?

all individuals detected from transect are counted

-density cannot be estimated

variable-width transect

-issue?

individuals are counted & perpendicular distance from line is measured

-difficult to estimate distance

fixed-width transect

-issue?

kinda like quadrat where individuals within borders are counted

-some species are detectable at greater distances

what is the best method for counting migrating animals?

single point counts

single point count

individuals are counted from a vantage point, like a watchtower

variable-radius point count

individuals counted from fixed point

-distance to individuals must be measured

fixed-radius point count

all individuals within a specific radius are counted

what is a metapopulation?

a group of partially isolated subpopulations interconnected by movement of individuals

characteristics of a source population?

1) habitat & resources are optimal

2) surplus offspring

characteristics of a sink population?

1) habitat & resources are poor

2) insufficient offspring

3) population sustained by immigrants from source populations

should conservationists focus on preserving areas where a species is most productive or most common?

most productive

Clumped spatial distribution(dispersion)

-what causes this?

individuals are in close proximity in groups

-most common spatial distribution

-usually due to social behavior or heterogeneity of environment

Uniform spatial distribution(dispersion)

-what causes this?

examples?

individuals are spaced evenly apart

-due to competition

ex// beehive, nesting seabird colonies

how are humans distributed ?

clumped

random spatial distribution(dispersion)

example?

individuals scattered randomly

ex// seeds disperse

temporal distribution?

distribution varies with time

characteristics of a rapid growth population?

-wide based pyramid (bc more offspring)

-LOT of offspring

characteristics of a slow-growth population?

-narrow-based pyramid

-fairly high number of offspring

characteristics of a stable/zero growth population

-skyscraper shaped (narrows at top)

-normal proportion of offspring produced

characteristics of declining/negative growth population

-narrow base & wide in the middle

-low offspring

how are tree rings formed?

fast xylem growth rate during growing season & slower rate during non-season

size of tree trunk measured by?

DBH (diameter at breast height)

is size of tree correlated with age?

no, bc growth rate varies

ex// saplings can grow very slow until a tree falls over & it suddenly gets a lot of sun

define demography?

study of populations