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Transcript
• 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) • e.g. predation, disease, competition – Abiotic factor - a non-living, physical factor that may influence an organism or an ecosystem (IB) – e.g. temperature, salinity, pH, light Ecosystems Chapter 3 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 • Ecological Niche: A species' share of a habitat and the resources in it. – An organism's ecological niche depends not only on where it lives but on the role it plays in the ecosystem. • Fundamental Niche: The part of the habitat in which a species can live in the absence of competitors and predators. • Realized Niche: The part of the habitat that the organism actually occupies. 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. • • • • • • Producers Herbivores Carnivores Decomposers Nutrient Pool Heat • 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 • Symbiosis • “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. MutualismInteraction between two species where both benefit – e.g. zooxanthellae in anemones & corals; nitrogen fixing bacteria in legumes; cleaner fish; lichen 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 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 Examples • Bacteria in hydrothermal vent tubeworms • Plasmodium falciparum (malaria-causing protozoan) in Homo sapiens Sea anemone and clownfish