 What determines the size of a population?  Limiting Factor – any factor that restricts the size of a population › Can be biotic, such as availability of food › Can be abiotic, such as access to water  Example: fish in a pond -why can’t there be 1000?

 Abiotic Factors such as light, temperature, and soil can influence a species’ ability to survive  Tolerance Range – the abiotic conditions that a species can survive in  Near the top and bottom limits, species will have poorer health, growth, and reproduction  In the middle range, species will be healthiest (optimal range)

 Too much to the left or right (extreme) has very low population

 Some species have broad tolerance ranges, while others have narrow  Species with a broad (wide) tolerance range will survive in more places › Example: Orchids (narrow) vs. grass (broad)  Orchids are fragile, need very specific conditions  Grass can grow anywhere

 In aquatic ecosystems, there are 2 main abiotic factors: › 1. Salt concentration › 2. Availability of oxygen, sunlight, and nutrients  Sunlight only travels so deep, so most oxygen is at the water’s surface for photosynthesis

TerrestrialAquatic -sunlight or shade-sunlight in water -water availability (rivers, etc) -nutrient availability -nutrient availability (in soils) -acidity (acid rain into lakes) -temperature -salinity (salt)

 Abiotic factors determine where a particular species can live  Biotic factors determine a species’ success › Example: a deer can survive in the abiotic conditions of a forest, but they are best suited for open woodlands (more food/watch for predators)

 The main biotic factor is interaction between species  Example: a birch tree and maple tree compete for sunlight and soil nutrients  Example: Squirrels compete with each other for food

RelationshipDefinitionExample

RelationshipDefinitionExample Competition2 individuals fight for the same resource -foxes and coyotes fight for mice and rabbits

RelationshipDefinitionExample Predation1 individual feeds on another -lynx prey on snowshoe hares

RelationshipDefinitionExample Mutualism2 individuals benefiting from each other -plants give us oxygen, we give plants carbon dioxide

RelationshipDefinitionExample Parasitism1 individual lives on/in a host organism -tapeworms are parasites of humans and pets

RelationshipDefinitionExample Commensalism1 individual benefits, the other is neutral -a bird uses a tree for a home, but the tree doesn’t benefit or get harmed

 As populations increase, so does the demand for food, water, shelter, and space › Eventually, there won’t be enough resources  Carrying Capacity – the maximum population that a given ecosystem can sustain › Example: can a tiny forest have 3000 grizzly bears? Why? What is the max? › Example: When planting vegetables in a garden, can you plant them super close together?