Investigating populations

Abundance - number of individuals of a species in a given space

 

QUADRATS

FACTORS TO CONSIDER

• SIZE OF QUADRAT TO USE
• NUMBER OF SAMPLE QUADRATS TO RECORD IN STUDY AREA - LARGER SAMPLE SIZE = MORE RELIABLE
• POSITION OF QUADRAT IN STUDY AREA - SHOULD BE RANDOM SAMPLE

RANDOM SAMPLING 

AVOID BIAS - ENSURE DATA VALID

IF INVESTIGATING ANIMALS IN SAME TYPE OF HABITAT, CHOOSE TWO CLOSE TOGETHER TO MINIMISE ABIOTIC DIFFERENCES

 

1. LAY OUT 2 LONG TAPE MEASURES AT RIGHT ANGLES, ALONG TWO SIDES OF STUDY AREA
2. OBTAIN SERIES OF COORDINATES, USE RANDOM NUMBERS TAKEN BY RANDOM NUMBER GENERATOR ON COMPUTER
3. PLATE QUADRAT AT INTERSECTION OF EACH PAIR OF COORDINATES, RECORD SPECIES WITHIN IT.

Point quadrat - HORIZONTAL BAR SUPPORTED BY 2 LEGS, SET INTERVALS ARE HOLES, THROUGH WHICH A PIN CAN BE DROPPED - EACH SPECIES THE PIN TOUCHES IS RECORDED

Frame quadrat - SQUARE FRAME, DIVIDED INTO SMALL EQUAL SUBDIVISIONS, PLACED IN DIFFERENT LOCATIONS, ABUNDANCE OF EACH SPECIES WITHIN EACH QUADRAT RECORDED, E.G ONLY SQUARES CONTAINING OVER 50% COVERAGE COUNTED

Belt transect - TWO PARALLEL STRIPS, SPECIES OCCURRING WITHIN LINES RECORDED

 

SYSTEMATIC SAMPLING - FOR WHEN THERE IS TRANSITION IN A COMMUNITY, SUCH AS DISTRIBUTION CHANGE AS ALTITUDE INCREASES UP A HILL. STAGES OF ZONATION ESPECIALLY WELL SHOWN USING TRANSECTS

Abundance - number of individuals of a species within a given space

 

Limitations of frequency measurement - good if a species hard to count, but does not provide info on density and detailed distribution

Percentage cover - data collected rapidly, individual plants don't need to be counted, but less useful when organisms occur in several overlapping layers 

 

MARK, RELEASE,RECAPTURE

KNOWN NUMBER OF ANIMALS CAUGHT AND MARKED IN SOME WAY, AND RELEASED. AFTER A SET TIME, A GIVEN NUMBER OF INDIVIDUALS COLLECTED RANDOMLY, MARKED INDIVUDUALS NUMBER RECORDED.

 

ESTIMATED POPULATION SIZE = TOTAL NUMBER OF INDIVIDUALS IN FIRST SAMPLE X TOTAL NUMBER OF INDIVIDUALS IN SECOND SAMPLE / NUMBER OF MARKED INDIVIDUALS RECAPTURED

 

ASSUMPTIONS:

• PROPORTION OF MARKED TO UNMARKED INDIVIDUALS IN SECOND SAMPLE SAME PROPORTION OF MARKED TO UNMARKED IN POPULATION AS WHOLE
• MARKED INDIVIDUALS RELEASED FROM FIRST SAMPLE DISTRIBUTE EVENLY AND HAVE SUFFICIENT TIME TO DO SO
• POPULATION HAS DEFINITE BOUNDARY SO THERE IS NO IMMIGRATION OR EMIGRATION WITHIN POPULATION
• FEW DEATHS OR BIRTHS
• METHOD OF MARKING NOT TOXIC OR MAKE THE INDIVIDUAL MORE CONSPICUOUS AND LIABLE TO PREDATION
• MARK NOT LOST OR RUBBED OFF DURING IVESTIGATION

 

 

CORRELATION - WHEN TWO FACTORS VARY IN RELATION TO EACH OTHER

 

CONSERVATION RULES DURING INVESTIGATIONS

• ORGANISMS STUDIED IN SITU - NOT REMOVED - OTHERWISE KEEP NUMBERS TO MINIMUM
• RETURN REMOVED ORGANISMS TO SITE, EVEN IF DEAD
• SUFFICIENT PERIOD OF TIME SHOULD ELAPSE BEFORE SITE USED FOR FUTURE STUDIES
• AVOID DAMAGE AND DISTURBANCE TO SITE

BALANCE BETWEEN DAMAGE DONE AND VALUE OF INFO GAINED