Why Fertilize? Nutrient Limitation most soils are in need of one major nutrient. growth is limited until that nutrient is obtained. most fertilizers have large amounts of N, P, and K (the “macronutrients”) micronutrients are also needed but in smaller amounts (Ca, Mg, S, Fe, Mn) all nutrients work like “interlocking gears”. if one nutrient is in short supply, the wheels get “stuck” until the element is obtained and growth can resume.

4.2 Niches and Community Interactions Where an organism can live depends on what conditions it can tolerate this will determine which habitat it can occupy niche: where a species lives and HOW it makes a living (how it survives) resources in a niche: water, food, light, space, etc. physical aspects of a niche: involve abiotic factors needed to survive biological aspects: involve the biological factors needed to survive. (when and where reproduction can happens, food to eat, how to get that food) ex: all birds on Christmas Island live in same habitat but prey on different sized fish in different places. Thus, each species occupies a different niche.

Competition shapes communities limited resources force competition among living things in same niche. among same species = intraspecific competition between different species = interspecific competition all competition almost always produces a winner and a loser (dies out) ex: two species of paramecium kept in same culture…one species out competed the other. the competitive exclusion principle: no two species can occupy the same niche at the same time. dividing resources can be a “truce” in the competition for resources ex: one spruce tree can provide for three different niches of warbler birds feeding on high, middle, and low branches ** by dividing resources, competition helps determine the number and types of species in a community AND the niche each species occupies

Predation, Herbivory and Keystone Species predator-prey: predators affect the amount of prey and where prey can live and feed herbivore-plant: herbivores affect both the size and distribution of plants and determine where those plants can grow keystone species: a change in one species can have drastic effects on many other species in the community ex: Pacific NW: sea urchins eat giant kelp stalks. Sea otters eat sea urchins. Otters are a keystone species- they keep the sea urchin population in check Over hunting of the otters allowed urchin population to explode  giant kelp forests destroyed by urchin activity with no kelp, many animals were without a habitat otters are now protected species, urchin population is under control and kelp forests have rebounded

Symbiotic Relationships symbiosis = “together living”. any relationship where 2 species live in close association with each other. 3 main types of symbiotic relationships: A) mutualism (“win-win”): Both benefit. ex: sea anemone and clown fish. Clown fish gets a protected home and the anemone gets a defender when attacked B) parasitism (“win-lose”): One benefits at the harm of the other (host) ex: tapeworm inside a human. Tapeworm absorbs digested food of host, the host’s cells starved for nutrition. C) commensalism (“win-no harm/help”): One benefits while the other is neither harmed nor helped ex: barnacles on a whale. Barnacles benefit by motion of whale and the movement of food particles over them. No benefit or harm comes to the whale.

4.3 Ecological Succession: Primary and Secondary a progressive, predictable ecological change in a community over time In 1833, volcanic island of Krakatau completely destroyed by an eruption – left completely barren. 2 years later, grasses are present 14 years later, 49 plant species and lizards, birds, insects, and bats by 1929, a forest with 300 plant species were present. today the island is a mature rainforest HOW?: Primary Succession: – begins with no remnants of the previous community –pioneer species are first to colonize barren land –ex: lichen (fungus and algae) turn rock into soil, turn N 2 gas into useful nitrogen forms, and add organic material to the soil –certain grasses are also pioneer species

Secondary succession: occurs after a major event disturbs a community (fire, flood, earthquake, hurricane) SOIL survives the disturbance plants re-colonize the area faster than in primary succession can also follow human activities like forest clearing and farming once plants are established, herbivores can move in and make use of the food supply. Then, carnivores can move in if ecosystem is healthy, it may be restored to its natural state prior to disturbance (the “climax” community) sometimes the human impact is to traumatic, a full recovery through succession is not possible 4.3 Ecological Succession: Primary and Secondary