back to Wildlife Ecology and Management

elective course

Why study populations?

To understand how it works. „basic research”
To predict future „applied research”
To manage. „application”

Factors to be considered

Number of animals (density)
Available food
Habitat use
Condition
Fertility
Mortality
Age, gender

Limitations

One cannot study "everything": data is costly
We need a goal
Formulate a hypothesis
Decide the nature of data needed
Choose methods
Get data
Analyze
Test your hypothesis

Sampling:
precision (random error) and bias (systematic error)

Heterogeneous population (all dogs): large variance
Focus your sample (only vizslas): small variance
However, narrow population, narrow validity
Solution: stratify!

3 different habitats + road
identify strata

systematic sampling: easier, however, if distribution is not random, sample might not be representative.

random sample: representative

Density estimation, some methods

Absolute density not needed, or not feasible: INDICES
All individuals seen, on whole area: Complete census (zoo park)
All individuals seen , on sample plots: Counts on Stripes, Quadrats, Line-transect
Not all individuals seen, animals can be captured: capture-recapture methods

Absolute density not needed, or not feasible: INDICES

Road counts, pellet counts, calls detected
Relation with true density in not known
Type of data:
Area A > area B, 2000 > 2001

see here for an example of road count with the participation of the public
go here to see how owls were surveyed by recording their sound on a standard transect line

All individuals seen , on sample plots

Counts on Stripes, Quadrats, Line-transect
(True census on plots with delectability = 1, density estimated for whole area)

LINE TRANSECT
Position lines, (stratified random?)
Detectability on line = 1
Detectability diminishes by distance

estimate distance and angle. calculate perpendicular distance from line

sighting of a group is a single sighting! (calculate average groups size)

estimate distribution of distance data.

Advantages of line transect:
realistic requirement (all animals seen on line) vs all animals seen on stripe

WWW
software to evaluate distance data

Not all individuals seen, animals can be captured: capture-recapture methods

Animals captured and marked.
Animals released and recaptured. Ratio of marked individuals in recaptured sample is known.

100 recaptured with 10 individuals marked: estimation is 1000 individuals

Not so simple as this (closed population, probability of capturing marked or unmarked individuals is equal)

introduction to method + software www

Capturing animals

Birds

mist nets for smaller birds
traps for larger birds
Net Capture Guns

details on tools at Smithsonian

Mammals

live traps
drop net (see figure)
chemical immobilization (in food, shot syringe)

Photos on caribou immobilization and marking: www

Radiotelemetry

transmitters, fitted on collar www
weight of transmitter is critical

receiver with direction sensitive antenna

Physiological data: Activity, Temperature, Heart rate, ECG, EEG, muscle activity, Water, Light (rabbit), Pressure (air or water)

Marking

birds: rings, wingtag, dyes, radiotransmitter
more on Bird marking www

mammals: freeze band, dyes, collars, eartags

Condition

kidney fat index (kidney fat / kidney weight), correlates with body fat ratio.
floor effect: kidney fat depletes early (use bone marrow)

Age

Continuous variables (eye lense mass, body size of fishes, stature, antler, tooth ware www etc.) can be used to estimate age categories

Discrete variables: Plumage of birds ( yearling vs. old), tooth replacement (precision by month at young agespecies specific), ossification (young or old)

Figure illustrates ossification of radius and ulna of the European hare according to G. Kovacs. By cca 8 month of age the bump disappears.

Diet analysis

Direct
Observation (semi-tame animals)
Choice tests (tame animals)

Post-ingeston samples
Feces (herbivores and carnivores)
Regurgitated pellets (carnivores, birds of prey)
Remains (bones) or marks (browsed twigs)
Stomach content

Herbivores
Feces: microhistology
Washing, Homogenizing, Clearing, Staining, Mounting.
Remains identified by species under microscope

Study these 3 plant species. Try to match them with the corresponding microhistology pics.
hint: go to source by clicking at the images

Fraxinus pennsylvanica (click)

Pictures were kindly provided by
dr. Katalin Mátrai

Fertility

Analyis of follicles
Ovulation ? Corpus Luteum (yellow body)
In large and medium sized animals
Indicates ovulation rate.
May overestimate fertility

CL: corpora lutea

Placental scars: Detachment of placenta
For certain species: Rodents, bats, insectivores, lagomorpha, carnivores
European hare: all young within 9 months

Hormone profiles: LH surge prior to ovulation
For monitoring captive animals
Metabolites estimated from fecal samples

worked out for many species

Direct observation: depends on species and habitat
Calves and fawns hide, difficult to find them

Mortality

difficult to locate dead animals
indirect estimation: number of animals missing
direct observations: for some species in open habitat
experiments: artificial nests