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Why Fertilize? Nutrient Limitation
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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
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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 N2 gas into
useful nitrogen forms, and add organic material to the soil
– certain grasses are also pioneer species
4.3 Ecological Succession: Primary and Secondary
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