III. PARTS OF AN ECOSYSTEM

A) ABIOTIC FACTORS

* the non-living parts of the environment
* they directly affect the ability of organisms to live and reproduce
* abiotic factors can vary from place to place

* abiotic factors can act as LIMITING FACTORS that keep a population at a certain level

ex. desert environment -- hot temperature and little water are examples of limiting factors -- different species living in the desert are LIMITED mainly to those types of plants and animals that need very little water and can survive extreme temperatures


B) BIOTIC FACTORS

* all the living things that directly or indirectly affect the ecosystem
* biotic factors interact with other living organisms and the physical environment

* can also be LIMITING FACTORS

ex. disease (bacteria), predators, food resources

there are 2 types of ways biotic factors interact: nutritional and symbiotic relationships
1) nutritional relationships:

* involves the transfer of nutrients from one organism to another within an ecosystem

a) AUTOTROPHS--
* organisms that can synthesize organic molecules from inorganic molecules
* also called producers
* can be either photosynthetic or chemosynthetic

b) HETEROTROPHS--
* organisms that cannot manufacture organic molecules
* there are 5 types of heterotrophs

i. HERBIVORES--
* organisms that eat only producers (plants)
* also called a primary or first-level consumer
ex. cows, elephants, goats

ii. CARNIVORES--
* organisms that eat only other animals
* also called a secondary (or tertiary--3) consumer
ex. tigers, lions, wolves

iii. OMNIVORES--
* organisms that eat everything
* can be a 1st, 2nd, or 3rd level consumer
ex. bears, humans

iv. SCAVENGERS--
* organisms that eat only other animals after they are already killed
* usually a 2nd or 3rd level consumer
ex. vultures, hyenas

v. DECOMPOSERS--
* organisms that live on DEAD matter
* also called saprophytes
ex. include heterotrophic plants, fungi, and bacteria

FOOD CHAIN
* always starts with producers
* shows the pathway of energy from one organism to the next in a direct line of organisms

FOOD WEB
* shows the interactions and interconnections among the different food chains of a community


2) symbiotic relationships:
* an interaction among different species in an ecosystem that where they live in a close association with each other
* called SYMBIOSIS; at least one member of the association benefits (gains) by the association

a) MUTUALISM (+ , +)
* a symbiotic relationship in which both organisms BENEFIT
ex. nitrogen fixing bacteria that live in nodes (lumps) on the roots of certain plants (legumes)...the bacteria have a nice place to live (+), and the plants benefit from getting the nitrogen they need from the bacteria (+)

b) COMMENSALISM (+ , 0)
* a symbiotic relationship where one organism benefits (+) and the other organism is not harmed (0)
ex. the remora (a small fish) attaches itself to the underside of a shark...when the shark feeds, the remora disconnects and eats scraps that are left over (+) ... the shark is not affected (0); barnacles (+) on whales (0)

c) PARASITISM (+ , -)
* a symbiotic relationship where one organism, the parasite, benefits (+), while the other organism, the host, is harmed (-)
ex. athlete's foot, a fungus, grows on human feet for nutrients (+), while the human doesn't like it (-);
tapeworms (+) in humans (-); heartworms (+) in dogs (-)

d) PREDATOR-PREY (+, -)
* a symbiotic relationship where one organism eats another!
ex. predator--lions (+), prey--gazelles (-)

Ecology