Variation in population size

POPULATION - GROUP OF INTERBREEDING INDIVIDUALS OF SAME SPECIES IN HABITAT - POPULATION SIZE = NUMBER OF INDIVIDUALS IN A POPULATION

GROWTH CURVES

1. PERIOD OF SLOW GROWTH AS SMALL NUMBER OF INDIVUDALS REPRODUCE TO SLOWLY ESTABLISH NUMBERS
2. PERIOD OF RAPID GROWTH, EVER INCREASING NUMBER OF INDIVIDUALS REPRODUCE, POP. SIZE DOUBLES DURING EACH INTERVAL OF TIME
3. POP GROWTH DECLINES, SIZE REMAINS STABLE, CYCLIC FLUCTUATIONS DUE TO PREDATION POP SIZE AND FOOD SUPPLY, DECLINE DUE TO INCREASED PREDATIONOR LIMITING FOOD SUPPLY. CARRYING CAPACITY REACHED

WHY POPULATION GROWTH REDUCES (ALGAE)

• MINERAL IONS USED UP AS POPULATION GETS LARGER
• POPULATION SO LARGE THAT ALGAE AT SURFACE PREVENT LIGHT REACH THOSE AT DEEPER LEVELS
• OTHER SPECIES INTRODUCED TO POND, MAY USE ALGAE AS FOOD OR COMPETE FOR LIGHT/MINERALS
• WINTER BRINGS LOWER TEMPS AND LOWER LIGHT INTENSITY OF SHORTER DURATION

A SPECIES CAN ONLY LIVE WITHIN A RANGE OF ABITOIC FACTORS THAT LIMIT THEM, AND GROWTH IS LIMITED BY A LIMITING FACTOR

ABIOTIC FACTORS

TEMPERATURE - EACH SPECIES HAS DIFFERENT OPTIMUM TEMP TO BEST SURVIVE. AS TEMPS FALL BELOW OPTIMUM, ENZYMES WORK MORE SLOWLY, METABOLIC RATE REDUCED. ABOVE OPTIMUM, ENZYMES WORK LESS EFFICIENTLY, UNDERGO DENATURATION

IN WARM BLOODED ANIMALS, MORE ENERGY EXPENDED TO MAINTAIN NORMAL BODY TEMP - LESS ENERGY FOR GROWTH AND REPRODUCTIVE RATE SLOW

LIGHT - ULTIMATE SOURCE OF ENERGY FOR ECOSYSTEMS (ALL INTERACTING BIOTIC/ABIOTIC FACTORS). RATE OF PHOTOSYNTHESIS INCREASES AS LIGHT INTENSITY INCREASES, MEANS MORE SPORE/ SEED PRODUCTION AND GROWTH, POP OF PREDATORS LARGER

PH - AFFECTS ENZYME ACTION IF ABOVE OR BELOW OPTIMUM

WATER AND HUMIDITY - AFFECTS TRANSPIRATION RATES AND EVAPORATION OF WATER FROM BODIES. IF WATER SCARCE LESS ORGANISMS. TOLERATION AND ADAPTATION.