Ecosystems Ecology PDF

Ecosystems Ecology Michael Dann A. Superio Instructor I Ecosystem Species interacting with their abiotic and abiotic factors  Coined by Tansley (1935)  Biotic + abiotic factors  Applies to any scale: drop of water, your skin, a forest  T...

Ecosystems Ecology Michael Dann A. Superio Instructor I Ecosystem Species interacting with their abiotic and abiotic factors  Coined by Tansley (1935)  Biotic + abiotic factors  Applies to any scale: drop of water, your skin, a forest  Three major constituents  Biomass composed of carbon and nitrogen  Energy flow  Availability of rare chemicals or minerals TROPHIC STRUCTURE Transfer of energy from one level to another feeding relationships of organisms Trophic Structure Trophic Levels Two ways to derive energy: harness it from nonliving sources, or harness it from other living organisms. Autotrophy Heterotrophy pick energy from the sun eat living matter (predator) or dead (photoautotrophs) or organic and materials originally from living organisms inorganic matter (chemoautotrophs) (saprophytes and decomposers) Trophic Structure Trophic Levels  Trophic level of a species is one more than the chain length.  Chains are short; not more than 5 or 6 links.  Important links are those involving detritivores. Feeds on shits and debris  Detritivores release locked nitrogen and phosphorus back into the system Trophic Structure Food Webs  The interconnection of many food chain = food web  Most complete food web are extremely complicated.  Three types of food web source-consumer  Source webs: the sources and their consumers consumer-source  Sink webs: the consumers and their prey  Community webs: group of species within a defined area or habitat Trophic Structure Food Webs  Can form useful starting point for the analysis of ecosystem organization  Relative complexity of a food web is known as connectance 𝑎𝑐𝑡𝑢𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑡𝑒𝑟𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛𝑠 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑎𝑛𝑐𝑒 = 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑡𝑒𝑟𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛𝑠 𝑛(𝑛−1) Calculation of potential: 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑖𝑛𝑡𝑒𝑟𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛 = 2  Number of links per species is known as linkage density (d) 𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑐𝑡𝑢𝑎𝑙 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑑= 𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑝𝑒𝑐𝑖𝑒𝑠  Relative linkage density: number of links a species has relative to the total number of links in the web Trophic Structure Food Webs Generalization about food webs  Cycles are rare. That is species A eats species B which then eats species A which in turn consumes species A.  The average proportion of top predators (apex), intermediate species (in- between), and basal species (autotrophs) remains constant in webs regardless of the number of species.  The proportion of trophic links between top predators and intermediates, intermediates and intermediates, basal species and intermediates, and basal to top remains constant.  Linkage density is often constant, except for webs with large numbers of species. It is invariant and is roughly equal to 2. Trophic Structure Food Webs Generalization about food webs  Connectance remains constant as the number of species in the food web increases.  Omnivory is rare.  Food chain lengths do no differ greatly among ecosystems with different primary productivity.  There are only slight different in chain lengths where consumers are vertebrates, compared with where they are all invertebrates.  Chain length is smaller on smaller islands.  Chains are shorter in areas with frequent natural or experimental disturbances. Trophic Structure Food Webs Generalization about food webs  Chains are shorter in two-dimensional habitats such as grasslands than three-dimensional habitats such as forests or reefs.  The ratio of the number of prey to the number of predators is about one to one. Trophic Structure Food Webs Problems with the Food Web Theory 1. Predation on “minor” species is often omitted; linkages are often informal and idiosyncratic. 2. Data on quantities of food consumed, that is, thickness of links, are usually absent. 3. There is little data on the importance of chemical nutrients. One link may be important if it supplies a very important chemical nutrient. 4. There is little data on temporal variation. Some species may constitute a large proportion of the year at one time but not at other times. 5. Where does detritus fit? Trophic Structure Food Webs Problems with the Food Web Theory 6. Species are aggregated into “trophic species”; one may not know the important biology in many of these links. 7. It is hard to define web boundaries. 8. Many species exhibit age or size-related changes in diet and are not easily assigned to a single position in a web. 9. Many individuals do not fit in a discrete trophic level. 10. Constancy of the 1:1 predator-prey ration may be an arithmetical artifact; many taxa can be recorded as a predator and a prey and can hence be double counted. Trophic Structure Guilds  Functional units of a food web  Species that exploit the same resources in a food web.  Another type of classification for roles in the web. GUILD SPECIES Fruit-eating Bats birds Frugivores Monkeys Lemurs Earthworm Dung beetle Detritivores Sea star Pill bugs ENERGY AND NUTRIENT FLOW How energy and nutrients flow in an ecosystem Laws of Thermodynamics  First Law: Law of Conservation of Energy “Energy cannot be created nor destroyed; it can only be transformed from one form to another.” Laws of Thermodynamics  Second Law: Law of Entropy energy loss due to no one will consume heat (excess energy) “In every energy transformation, potential energy is reduced because heat energy is lost from the system in the process.” Primary Production  Photosynthesis: the cornerstone of all life and the starting point for studies of community metabolism.  Gross primary production: equivalent to the energy fixed in photosynthesis  Net primary production: gross primary production minus the energy lost by plant respiration. Secondary Production  Biomass of plants upon consumption of herbivores or detritivores  In turn, herbivore is consumed by carnivores Nutrient Cycles  Ecosystems can be best understood not by the flow of energy but by the cycle of nutrients  Biogeochemical cycle: the recycling of nutrients in the ecosystem. It is the turnover of substances in a pathway by which a chemical substance moves Rocks may rise due to earthquake or eruption N fixation Nitrification Assimilation Ammonification Denitrification Summary  In ecosystems, energy is lost with each transfer up the food chain.  In most ecosystems, plant material does not go to herbivores but to decomposers after the plant dies.  In general, primary production is highest in tropical forests and decreases progressively towards the poles.  Nutrient deficiency, particularly nitrogen and phosphorus, can limit primary production.  The limit to secondary production is the availability of primary productivity.  Nutrients may cycle locally or globally.  Phosphorus cycle is simple because it does not have atmospheric component.  In carbon cycle, carbon dioxide content is low in atmosphere and higher in plants.  Nitrogen cycle is global; has five steps: N fixation, nitrification, assimilation, ammonification, denitrification.