SGCEP SCIE 1121 Environmental Science Spring 2012 Section 20531 Steve Thompson: steventhompson@sgc.edu http://www.bioinfo4u.net/ 1
Ecosystems, energy flows, and biomes Today s going to be a bit different. First I want to fly through a bunch of definitions, quite quickly; however, you are responsible for them they are important, and will be on the exam. And then we ll watch most of a great documentary from Planet Earth! 2
Ecosystem definitions Trophic levels (think feed trough)... Autotrophs: produce organic material from inorganic substances through the use of an external energy source, usually the sun; these are also called producers. This includes all green plants, and many single-celled protists, archaea, and bacteria. Primary production: essential production of organic matter through photosynthesis or chemosynthesis. Heterotrophs: must consume organic material to obtain energy. This includes... Consumers: eat living prey, either primary consumer (herbivore), or carnivore or omnivore, and... Plus... 3
The all important decomposers Detritus: high potential energy organic wastes, includes dead organisms and parts of organisms and feces. Decomposers recycle these nutrients through the ecosystem. Decomposers include Scavengers (e.g. vultures): break down large pieces of detritus; Detritus feeders (e.g. earthworms): eat partly decomposed matter; and... Chemical decomposers (fungi, archaea and bacteria): break down detritus chemically. 4
Decomp really matters! 5
These all interconnect in... Food chains: describe where energy and nutrients go as they move from one organism to another. Energy moves up the food chain. Not all energy and nutrients are passed to other levels. Much is lost at each step. Food web: an interconnection of food chains to form complex webs of feeding relationships within particular ecosystems. 6
For example, food webs in an agricultural area and the Arctic ocean. 7
Limits on trophic levels Terrestrial ecosystems usually have three or four trophic levels. Marine systems sometimes have five. Biomass: the total combined (net dry) weight of organisms Each higher trophic level has about 90% less biomass. This is because... There is a huge inefficiency at each trophic level. Only a small fraction of energy is passed on when energy flows from one trophic level to the next. Much of the biomass is not consumed by herbivores; Some food is used as energy to fuel the hetrotroph s cells and tissues, grow, and reproduce; plus... Some food is not digested and is excreted as waste. 8
From ecosystems to biomes Broad ecosystem patterns translate into a predictable set of organisms that live under particular conditions. Biomes: the different climatically and geographically defined major ecosystem areas of the Earth. See http://en.wikipedia.org/wiki/biome 9
Six major terrestrial biomes Desert: regions with less than 10 in of rain/yr; some hot, some cold; thin, poor soils. Grassland (prairie) biome: 10 to 60 in seasonal rain/yr; rich deep soils. Tropical rain forests: more than 95 in rain/yr; nonseasonal, quite warm and humid; thin, poor soils. Temperate deciduous forest: 30 80 in rain/yr; distinct seasons; good soils. Coniferous forests: often no free water in winter; harsh, cold winters with short summers; acidic soils. Tundra biome: little free water; bitter cold most of the year; only small plants that can grow in short summer above the permafrost. 10
The major terrestrial biomes 11
Aquatic systems Aquatic and wetland ecosystems are determined by depth, salinity, and permanence of water. Six major types Freshwater standing in lakes and ponds; Freshwater flowing in streams and rivers; Freshwater standing or flowing in wetlands, swamps, and marshes, high productivity; Salt and freshwater mixing in estuaries, high productivity; Coastal saltwater ocean, high productivity; Open saltwater ocean, low productivity. 12
Ecosystem disturbance Ecological succession: transition from one biotic community to another (terrestrial or aquatic). Pioneer species: colonize a newly opened area first creating conditions favorable to other species. Climax ecosystem: the eventual, relatively stable assemblage of species after succession in an area. Even these communities experience change if new species are introduced or old ones are removed. Primary succession: the process of initial invasion and progression from one biotic community to another in an area lacking all plants and soil (e.g., a retreating glacier) Secondary succession: an area cleared by some disturbance (e.g. fire, floods, humans) is reinvaded by plants and animals from surrounding areas. Starts with pre-existing soils and some biota. 13
Fire and succession Fire is a major form of disturbance. Decades ago, forest managers thought all fire was bad; But this accumulated deadwood encourage insects and disease to attack trees; And if a fire did occur, it was way worse because of all the accumulated tinder. Different species have different tolerances to fire: Grasses and pines tolerate fire, some even need it to germinate; But, deciduous trees are damaged by fire. Fire releases nutrients, and creates meadows supporting higher biodiversity. Fire climax ecosystems: ecosystems that depend on fire to maintain their existence (e.g., some grasslands and pine forests) 14
As we ve seen, there s all sorts of ecosystems, all around the world. But as I ve complained, this book tries to do way too much, so... Let s take the time to watch an episode of the excellent series, the BBC s Planet Earth, on one of the most biodiverse terrestrial ecosystems of the world, the rainforest! We ll discuss aspects of this film in the lecture next time, when we ll pick back up the text with Chapter 6. 15
So here it is... Episode 8, Jungles, of the 11 part British Broadcasting Corporation s series Planet Earth, narrated by David Attenborough. It used to be here: http://video.google.com/videoplay? docid=-2934374342545375813#... But copyright infringement most likely took it down. So I purchased the real thing. If you re curious about the series, the Wikipedia page has a great story on it: http://en.wikipedia.org/wiki/planet_earth_ (TV_series) 16