ecosystem *TRUE*

Topic 2 - The Ecosystem

·         Syllabus: Topics 2.1.1-2.1.3, 2.1.10, 2.2.1, 2.2.3

·         Reading:

o   Environmental Science (Wright and Nebel, 8th edition)   pp. 23-40

o   Biology (Campbell) pp. 1131-1134 (ecosystems);     1109-1114 (symbioses)

Topic 2: The Ecosystem

·         Ecosystem - a community of interdependent organisms and the physical environment they inhabit (IB)

·         Biotic & abiotic components of ecosystems

·         Biotic factor - a living, biological factor that may influence an organism or an ecosystem (IB)

o   e.g. predation, disease, competition

·         Abiotic factor - a non-living, physical factor that may influence an organism or an ecosystem (IB)

o   e.g. temperature, salinity, pH, light

Ecosystem structure

·         Often described based on feeding relationships

·         Species can be divided into trophic levels based on their main source of nutrition

·         Trophic level - the position that an organism occupies in a food chain OR a group of organisms in the community that occupy the same position in food chains

·         The trophic level that ultimately supports all others consists of autotrophs (primary producers)

Producer

·         Autotroph - “self” + “feed”

·         An organism that obtains organic food molecules without eating other organisms but by using energy from the sun or inorganic molecules to make organic molecules

·         Remember: this trophic level supports all others

·         Role of producers is to convert energy into a form useable for other organisms

·         Most producers are photosynthetic (e.g. algae, mosses, diatoms, some bacteria, plants etc.) but some are chemosynthetic (e.g. hydrothermal vent bacteria)

Consumer

·         Heterotroph - “other” + “feed”

·         An organism that obtains its nutrition by eating other organisms

·         Primary consumer (herbivore) - eats producers e.g. sea urchin, copepod

·         Secondary consumer (carnivore) - eats primary consumers e.g. wolf eel, herring

·         Tertiary consumer - eats secondary consumers e.g. sea otter, seal

·         Quaternary consumer - eats tertiary consumers e.g. killer whale

·         Role of consumers in an ecosystem is to transfer energy from one trophic level to the next

Decomposer

·         An organism that obtains energy by breaking down dead organic matter (including dead plants, dead animals and animal waste) into more simple substances

·         e.g. bacteria and fungi

·         Interconnect all trophic levels since the organic material making up all living organisms is eventually broken down

·         Role of decomposers is to return valuable nutrients to the system so they can be used again

Food chains and food webs

·         Few systems are so simple that they just consist of an unbranched food chain

·         Most are very complex as many species feed on more than one species and some consumers even feed at different trophic levels resulting in a food web

·         Food webs are more complex and therefore more stable

Energy flow through an ecosystem

An ecosystem’s trophic structure determines energy flow and nutrient cycling

Laws of thermodynamics

·         Remember them?

·         How do they apply to ecosystems?

·         First law - Energy is transferred from one trophic level to the next, energy is transformed from light to chemical (photosynthesis) and chemical to heat (respiration)

·         Second law - as energy flows through an ecosystem, much of it is lost at each trophic level

Rainbow trout in Northern Pike

Sysmbiosis

·         “sym” = together, “bio” = life

·         Relationship between two organisms that is not necessarily based on feeding

·         “An ecological relationship between organisms of two different species that live together in direct contact”

·         3 types of symbiosis - mutualism, commensalism, parasitism

1.       Mutualism

Interaction between two species where both benefit

–        e.g. zooxanthellae in anemones & corals; nitrogen fixing bacteria in legumes; cleaner fish; lichen

2.       Commensalism

Interaction between two organisms in which one species benefits while the other is unaffected

·         e.g. eyelash mites, orchids as epiphytes, remora on shark

3.       Parasitism

Interaction where one organism benefits while the other is harmed

·         e.g. tapeworm in human digestive system; leeches on fish; fleas on a dog; sea lettuce growing on bull kelp

Other symbiosis examples

·         Barnacles on whales

More examples

l          Bacteria in hydrothermal vent tubeworms

l          Plasmodium falciparum (malaria-causing protozoan) in Homo sapiens

l          Sea anemone and clownfish