Ecology Final Lessons 23 27 Lesson 23 Production Primary Production chemical energy generated by autotrophs derived from the fixation of carbon during photosynthesis and chemosynthesis it is the conversion of light energy from the sun into chemical energy that can be used by autotrophs and consumed by heterotrophs accounts for largest movement of carbon dioxide between earth and the atmosphere which influences global climate energy taken in by autotrophs stored as carbon compounds in plant tissues carbon is used for measurement of primary production rate of primary production primary productivity GPP gross primary production amount of carbon fixed by the autotrophs in an ecosystem GPP equal to total of all plant photosynthesis GPP controlled by o Climate through its influence on rates of photosynthesis o leaf area leaf area index LAI NPP net primary production balance between GPP and autotrophic respiration it is the amount of energy captured by autotrophs that results in an increase in living plant matter or biomass in other words NPP is energy left over for plant growth plant reproduction and consumption by herbivores and detritivores also represents total input of carbon into ecosystems Allocation of NPP in plants plants tend to allocate the most NPP to those tissues that acquire the resources that limit their growth ex plants in desert or tundra that lack water allocated NPP to their root growth instead of leaves and stems NEE net ecosystem production net ecosystem exchange net exchange of CO2 NEE GPP AR HR NEE provides a more refined estimate of ecosystem carbon storage than NPP because heterotrophic respiration is subtracted Aquatic Systems dominant autotrophs are phytoplankton including algae and cyanobacteria To measure NPP to estimate NPP harvest techniques are not used because the phytoplankton life span is too short so they have small biomass instead rates of photosynthesis and respiration are measured in bottles of water another way is remote sensing of chlorophyll concentrations in the oceans by measuring how much light is being absorbed reflected by chorophyll NPP is constrained by both physical and biotic environmental factors 1 NPP in terrestrial ecosystems is controlled by climate NPP increases as average annual precipitation increases up to a certain point then decreases in SOME ecosystems Why does it decrease o Cloud cover for a long time lowers available sunlight o High amount of rain leaches nutrients from soil o Too much water in soil hypoxic conditions for plants NPP increases with average annual temperature Does not mean that NEE ecosystem carbon storage does the same increasing temp leads to increased heterotrophic respiration and loss of carbon so therefore NEE decreases 2 NPP in aquatic ecosystems is controlled by nutrient availability a Primary producers in lakes are phytoplankton and rooted macrophytes b NPP in streams and rivers often low i Most of its energy from terrestrial organic matter ii Water movement limits amount of phytoplankton iii Most NPP comes from photosynthesis by macrophytes and algae at the bottom in shallow areas where there is enough light for photosynthesis iv Nitrogen and phosphorous can limit NPP i Estuaries are rich in nutrients relative to other marine c Marine NPP ecosytems ii Agricultural industrial activities have increases river inputs of nitrogen into estuaries lead to blooms of algae iii These blooms of algae from nitrogen being dumped into estuaries lead to dead zones areas of high fish and zooplankton mortality iv NPP in open ocean derived primarily from phytoplankton also from seaweed and kelp near shore v NPP is limited by nitrogen also in some ocean regions by iron Effect of iron fertilization on marine NPP 1993 was tested in an experiment the results of fertilizing surface water of the equatorial Pacific west with iron were doubling of phytoplankton biomass and increase in NPP Global patterns of NPP highest rates of NPP on land found in tropics because of long growing seasons high rate of precipitation oceanic NPP peaks at mid latittudes between 40 60 degrees o Peaks associated with zones of upwelling areas where ocean currents bring nutrient rich deep water to the surface Secondary Production Energy that is generated through the consumption of organic matter by heterotrophs heterotrophs include archaea bacteria fungi animals some plants 3 types of heterotrophs 1 Carnivores consume live animals 2 Herbivores consume plants and algae 3 Detritivores consume dead organic matter 4 Omnivores consume live organic matter How to determine heterotroph s diet 1 observe what they eat 2 3 measuring stable isotopes fecal material scat Net secondary production ingestion respiration egestion not all organic matter consumed by heterotrophs is incorporated into heterotroph biomass some used in respiration and egestion lost in urine or feces net secondary production represents greater fraction of NPP in aquatic ecosystems than it does in terrestrial ecosystems LECTURE 24 Energy flow and Food Webs Trophic levels 1st level autotrophs primary producers that generate chemical energy from sunlight or inorganic chemical compounds plantsSA dead organic matter detritus 2nd level herbivores which consume autotrophic biomass ex in the desert biome these are grasshoppers and mule deer o detritivores 3rd level carnivores that consume the trophic level below them includes small birds and scorpions 4th level foxes and birds of prey All organisms either consumed or end up as detritus in terrestrial ecosystems small portion of biomass is consumed the rest of energy flow passes through soil Dead plants microbial animal matter feces all consumed by detritivores process called DECOMPOSITION Energy flow through detritus is important for both terrestrial and aquatic ecosystems Terrestrial detritus comes from plants Aquatic input of detritus into streams lakes and estuaries comes from terrestrial organic matter considered EXTERNAL ENERGY INPUTS o ALSO called allochthonous inputs include plant leaves stems wood all fall into the water Energy Flow between trophic levels available energy decreases as you move up the trophic levels Trophic pyramids Terrestrial ecosystems you go up associated Aquatic ecosystems o Energy pyramid largest amount of energy at the bottom decreases as o Biomass pyramid same as energy biomass and energy are closely Energy energy produced by autotrophs is greater than heterotrophs o Biomass inverted high consumption rates and short