Population Parameters

1. Define population-group org. same spp. Occupying a particular space in time.

           a. Populations breed (potentially interbreed)

           b. Demes- same gene pool

2. How to characterize populations?

           a. Density

           b. Population parameters that affect density:

                       i. natality

                       ii. mortality

                       iii. immigration

                       iv. emigration

           c. Population characteristics

                       i. age distribution

                       ii. genetic composition

                       iii. distribution in space, time

3. Density measurements (populations)

           a. Unit problems

                       i. Unitary Organisms: Individuals (humans, birds)

                       ii. Modular Organisms: clonal (attached)

b.  Higher organisms are unitary through determinate growth.

c.  Plants are primarily modular organisms � develop into branched clones

                       -Aspen trees, not restricted to grasses

                       -Survive alone = ramets; genetic indiv. = genet

                       -Different approach sample population: biomass estimate vs #

d.  Not only plants recognized for modular � lower animals:

                       -Marine invertebrates: hydrozoans, corals, bryozoans

e.  How do we estimate populations?

f.  What do we need to consider? (problems of scale- the human perspective)

g. If want average densities particular spp.:

-correlations between parameters e.g. animal wt. & density

-Example: Mammals vs Birds log-log plots

            h.  Most cases do not rely on average densities:

                        -How population densities are changing? overfishing etc.

4. How do we measure population densities? 2 Approaches:

           a. Relative density (comparing one site to another)

           b. Absolute density (quantified unit #/hectare)

                       i.  Total counts (difficult for most org.)

                       ii. Sampling Methods (estimate total from sample)

                                   -Statistics becomes important � sample size

                       iii. Fixed organisms (quadrat sampling- benthic org.)

                                   -Size plots (km2) quadrat; 1m2

                       iv. Mobile organisms (capture & release)Absolute Density:  Measurements

5. Quadrat Sampling: Example of Quadrat sampling - Trees

Reliable estimates require:

1)      Population of each quadrat must be accurately determined

2)      The area of each quadrat is known

3)      The quadrats counted must be representative of the whole area (random sampling)

6. Capture-recapture method- Petersen 1898 (mobile animals � birds)

            Example: Capture-recapture method (Trout Norwegian Lakes)

            Example: Pigeons in Central Park - Ecobeaker program

7. Capture-recapture method:  Need consider:

                        a.  Closed populations � Not changing size during study

                        b.  Open populations � Death, Emigration marked Indiv.

                        c.   Multiple census � multiple yr, dynamics of population

                        d.   Open & dynamic capture-recapture models > complex

8. All capture-recapture models make 3-key assumptions:

            i.    Marked and unmarked animals captured randomly

            ii.   Marked animals subject to same or no mortality as unmarked

            iii.  Marked animals are neither lost nor over-looked

9. Indices of Relative Density:

�       Traps

�       Number of fecal pellets

�       Vocalization frequency

�       Pelt records

�       Catch per unit fishing effort

�       Number of artifacts

�       Questionnaires

�       Cover % - corals, benthic communities

�       Feeding Capacity

�       Roadside counts

�       etc.

10. Limitation to population approach:

           a. Determining boundaries of a population?

           b. Individual not always apparent:

                       i. Social insects

                       ii. Modular forms

           c. Biomass another averaging unit for clonal individuals (%cover)

           d. Population of species live within a larger community

 11. Advantage population approach:

           a. Models for population approach - principles on dynamics

           b. Population characteristics: sex, age, size imp. demography