Limits to growth Section 5.2

What factors control carrying capacity? Limiting factor = factor that controls the rate of growth of a population Examples Competition Predation Parasitism and disease Unusual Weather Natural disaster Can work separately or together – How do they each increase death rate in a population? Some depend of population density Limiting factors determine the carrying capacity of a community

Density dependent limiting factors Operate strongly only when population density reaches a certain level They do not affect small scattered populations as much Examples: Competition Predation Herbivory Parasitism Disease Stress from overcrowding

Competition In crowded populations, organisms compete for Food Water Sunlight Space Some organisms obtain enough for themselves Others enough to reproduce and support a family Others may starve to death

Why is competition density dependent? The more individuals the sooner they use up available resources Space and food are often related If no territory, cannot breed, no offspring Competition can also occur between different species fighting for the same resources Driving force for evolution – natural selection

Predation and Herbivory Wolves and moose – page 139

Humans as predators Humans can limit populations due to hunting, fishing, Example cod – new england Solution – stop eating cod!

Parasitism and disease Parasites have the power to weaken or kill an organism Diseases can wipe out entire populations

Stress from overcrowding Some species fight amongst themselves when overcrowded Fighting can cause stress This weakens the body and cause females to neglect or even kill offspring

Density independent limiting factor Affect all populations in similar ways regardless of population size and density Examples Unusual weather Natural disaster Initially after disaster population will crash Population may regrow quickly, or may take long time

Is a freak snow storm a density dependent or density independent limiting factor Depends on where the population are living? On an island, where emigration is not possible, it becomes a density dependent factor

Controlling induced species Limiting factors in one environment are not always present in the new environment Herbicides or mechanical removal are often only temporary measures In Florida – grass carp eat Hydrilla All introduced grass carp are sterilized – why?