ECOSYSTEM. Properties of the system are defined by the interactions of its subsystems

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1 ECOSYSTEM 1 ECOSYSTEM Properties of the system are defined by the interactions of its subsystems H. A. Gleason (1916, 1939): - Properties of plant community are just the sum of its parts, - Plant community is composed from randomly selected species that have adopted to prevailing environmental conditions on particular site, - Community is not handicapped if some of the species are eliminated from it F. E. Clements (1916, 1939): - Plant community is like living organism super-organism and its properties are defined by the interactions between the its components. 2 ECOSYSTEM Charles Elton (1927): - Trophic interactions between species are crucial for existence of plant or animal community - Pyramid of numbers is introduced as the indicator of the stability of community structure - Concepts of food chains and nutrient cycling are introduced in studies of communities 3 1

2 ECOSYSTEM John Phillipson (1934, 1935) upgraded Clement s ideas about community as functional unit / beginning with energetic studies of communities - Properties of the community are defined by interactions of its components and they are unpredictable 4 ECOSYSTEM Organisms that compose the community are under permanent influence of its environment and they make influence on the environment as well. Community and its physical environment are linked together=> sir Arthur George Tansley (Ecology 1935): " We can not separate (the organisms ) from their special environment with which they form one physical system it is the system so formed which (provides) the basic units of nature on the face of the earth These ECOSYSTEMS, as we may call them, are of the most various kinds and sizes" Bitoic and abiotic components of ecosystem can not be studied separately. Biotop + biocenosis = ecosystem (bio-geo-cenozis) 5 1. COMPONENTS OF ECOSYSTEM Biotic component = community - interacting organisms living in the area. Abiotic component = physical environment with which the organisms of community interact Three basic structural and functional components: 1. Autotrophs: energy capturing base of system: green plants and algae Heterotrophs: 2. consumers: feed on living tissue 3. decomposers: feed on dead matter or detritus that decompose it into inorganic substances 6 2

3 7 1. COMPONENTS OF ECOSYSTEM Inputs in ecosystem: Abiotic inputs: - energy (radiation => effects on temperature, humidity, photosynthesis), - inorganic substances (CO 2, N, O 2, minerals derived from weathering of the rocs) - organic compounds (proteins, carbohydrates, humic acids, organic matter), - precipitation Biotic: - organisms that move into ecosystem - other ecosystems in the landscape 8 1. COMPONENTS OF ECOSYSTEM The driving force is the energy of the sun. - it runs all internal cycles and exchanges with environment - Energy flow through the ecosystem and nutrients cycles are inseparable: the speed of nutrients recycle depends on consumers. Ecosystem is space unite (lakes, pounds, pasterns, forests) with relatively distances boundaries Ecosystem is time dependent dynamic system. 9 3

4 2. ENERGY Energy is defined as the ability to do work (1J=4.168 cal). Thermal energy sets the molecules into a state of random motion and vibration the hotter the object the more molecules are moving and vibrating. The energy of light waves causes electronic transition within atoms and molecules = excitation that leads to photochemical reactions = photosynthesis 10 b) Laws of thermodynamics Thermodynamics: science of complex systems that describes expenditure and storage of energy Thermodynamic laws: transformation of energies from one form into another and the efficiency of these transformations They base on empirical experiments and can not be mathematically proofed. All natural processes are obeyed to thermodynamic laws. 11 b) Laws of thermodynamics a) The first law concerns the conservation of energy. Energy is neither created nor destroyed, but it may change forms and pass from one place to another, or act on matter transforming energy of various ways. b) Second law concerns the efficiency of energy transformation from one form to another which is described by systems indicator entropy (Greek world entrope change). Ecosystem is open system and export of high entropy energy from the system (heat radiation) is the key process which enable its existence. 12 4

5 c) Energy flow through ecosystem Solar radiation is the ultimate source of energy for ecosystem. Plants use radiation of wavelengths between 400 and 700nm (photosynthetically active radiation) transformation of CO 2 into organic carbon compauds = source of energy for plants themselves and heterotrophs Energy flow is performed through chemical bound of organic carbon based compounds. Flow of energy through ecosystem is intimately related with solar radiation and carbon cycle which starts with primary producers plants PRIMARY PRODUCTION It starts with photosynthesis (kinetic energy of photon is transformed into energy of chemical bounds of carbon based compounds) Primary production: energy accumulated by plants: the first and the most basic form of energy storage in ecosystem Gross primary production (GPP): all energy that is assimilated by photosynthesis. Net primary production (NPP): GPP respiration; all living systems need energy for their existence. Production (gross or net) is measured as rate at which energy or matter is produced per unit area per unite time = productivity (kj/ m 2 /year or t dry matter / m 2 /year). The accumulation of biomass per unite area per unite time is called standing crop biomass usually expresed in t dry matter / m 2 14 a) Environmental controls on Primary production Productivity of terrestrial ecosystems is influenced by: - climate (combinations of average values of temperature, humidity, precipitation and wind speed) and - site s conditions (nutrients) 15 5

6 Net primary production depends on: Precipitation and temperature 16 Net primary production depends on: Length of photosynthetic period 17 Net primary production depends on: Evapotranspiration (transpiration from plants and surface evaporation => depends on temperature and precipitations) 18 6

7 Net primary production depends on: Nutrients (nitrogen mineralization rate) 19 b) Pattern of net primary production for different ecosystems Differences between ecosystems are huge: - Tropical rain forest : g/m 2 /year - Temperate deciduas forests : g/m 2 / year - Savanna: g/m 2 / year -Tundra: 144 g/m 2 / year -SCAN tab p

8 22 b) Pattern of net primary production for different ecosystems Time changes of net primary production depend on: - Age of prevailing type of the ecosystem - Ratio of gross production to respiration - Environmental conditions / constraints: (drought, fires, acid rain, )

9 c) Allocation of biomass in ecosystem Root to shoot ratios of the plants: - depends on availability of water, nutrients for plants and their request for physical stability Roots : above ground part: Tundra grasses 5-11:1, Tundra scrubs 4-10:1, Prairie grass 3:1, herbs 1:1 trees (beech: 13%, silver fir, spruce 15%) 0,2:1, 25 c) Allocation of biomass in ecosystem Vertical distribution. Assimilation apparatus are in the upper most layers, supporting systems that are just consumers of net production are located in lower layers

10 4. SECONDARY PRODUCTION Net primary production is the energy available to heterotrophic organisms but it may be also: - unavailable (herbivores), - flow from ecosystem (wind, water, humans), - grazers and carnivores feed on live organisms - decomposers feed on dead organisms - digestive efficiency depends on kind of food and properties of heterotrophs (grasshopper 30%, mouse 85-90% consumed food) White-tail deer Maintaining, growth and reproduction (energy storage) Inputs for detritovor (energy flow) SECONDARY PRODUCTION Energy left available to organism (respiration and metabolism) => production of tissues (growth) and reproduction => secondary production (depends on production efficiency = production/consumption) SECONDARY PRODUCTION Consumer s energy budget: C=A+(F+U) C-consumed energy, A-assimilated energy, F-feces, U-urine (nitrogenous wastes) A= P+R P-secondary production, R-aspiration U must be included into A => A=P+R+U U=> product of methabolic proceses but difficult to separate from feces wastes F => C= P+R+(F+U) Secondary production: P= C-R-(F+U) 30 10

11 4. SECONDARY PRODUCTION Secondary production depends on: - Food quantity, - Food quality, - Availability of net primary production => energy source, -Quantity of consumed food, assimilation efficiency and production efficiency Any restriction in primary production limits secondary production SECONDARY PRODUCTION Assimilation efficiency: how much of consumed food is converted in production (production to consumed) => efficiency of energy extraction from consumed food: Homotherms: 98% for metabolism, 2% for production Poikilotherms: 56% for methabolism,44% for production Production efficiency: production to assimilation => efficiency of consumers in incorporation assimilated energy into new tissues - Plants (net production / absorbed light): - phytoplankton: 0,34 % - plants: 0,9 % - Herbivorous : 5-16 % (homo poikilotherms) - Carnivores: % Food cheins Food cheins: Energy stored by plants is passed along through the ecosystem in a series of steps of eating and being eaten. Functional relations between organisms defined by throphic levels: organisms that obtain their energy in the same number of steps from the autotrops of primary producers belong to the same trophic level. First level: primary producers Second level: herbivores Third level: carnivores Some organisms occupy a single level, but some (omnivores) occupy more then one throphic level

12 5. Food chains a) Major food chains Two major food chains in ecosystem: - Grazing food chain (living plant tissues are the primary energy source for initial consumers herbivores) - Detrital food chain the initial consumers primary bacteria and fungi use dead organic matter as their source of energy) Food chains a) Major food chains 5. Food chains a) Major food chains In terrestrial ecosystems small proportion of primary production goes by way of the grazing food chain (2.6% of yellov poplar forest, 30 to 50% on heavily grazed prairie, from 33 to 66% in heavily grazed Serengeti plains of East Africa) => major activities of primary production is performed by detrital chain consists of nematodes, scarab, and ground beetles The idea that food chains involve animals of progressively larger sizes in true only in general way: snakes, parasites (fist level large animals are the base and as the number of links increases the body size decreases) Food chains a) Major food chains 36 12

13 5. Food chains a) Major food chains In very general way, energy transformed through the ecosystem by way of grazing chain is reduced by magnitude of 10 from one level to another => very few energy reach third level => energy chins have up to five levels Food chains Detrital food chain In terrestrial and littoral ecosystems it is the major pathway of energy - Gross primary production of forest ecosystem: 50% methabolisem and respiration, 13% new tissues, 2% herbivores, 35% detrital food chain - 3/4 primary production of grassland enters directly to detrital food chain. Supplementary food chains: parasites food chains and scavengers food chains are very complex => the total number of trophical levels increase significantly število!! Food chains Interactions between major food chains Chains are linked and combined => detrital food chain has feedback loop from carnivores to detritus => not in graying food chain!! 39 13

14 5. Ecological pyramids A) Pyramid of numbers: number of species decreased by increasing of trophical levels=> Elton 1927 B) Pyramid of biomass: Biomass decreases by trophical levels Pyramids of numbers and biomass show some information about structure but very little about functioning of ecosystem=> Pyramid of energy Ecological pyramids Pyramid of energy: stored energy at each trophical levels. P-primary producers C-consumers D-decomposers Ecosystem productivity Includes primary and secondary productivity Net ecosystem productivity: energy stored in living organisms and dead organic matter. It is expressed as the rate at which energy or mass is produced per unite area per time ( J/m2/year) Net ecosystem productivity: positive, zero, negative 42 14

15 43 7. Ecosystem Development What determines current state and direction? Current state = f (forming factors + history) Developmental trajectory = f( Endogenous factors (i.e. current state, internal feedback) Exogenous factors (external forcing, disturbance))??? 44 Development Δ in structure and function Mechanisms and patterns differ with levels of organization and scale Time Space 45 15

16 a) Changes occur at all scales in hierarchy Organisms/populations: Ontogeny, phylogeny Maturation (Ontogony) Time Community/ecosystems: Daily, seasonal & episodic change Ecosystem development Biosphere: Global chan. Population Organism Community Ecosystem Biosphere Ecological hierarchy Space Evolution (Phylogeny) Transcending principle: Large scale stability is contingent on small-scale change 46 b) Structural vs. functional development Structure: Δ in physical characteristics, composition and pattern Function: Δ in flows, cycling, control mechanisms Energy Matter 47 c) General trends in ecosystem development Strategy of ecosystem development (Odum 1969) Early Late %Solar energy trapped Low High Photosynthesis/Respiration <1 >1 =1 Biomass Low High Nutrient loss High Low Biotic regulation Low High (+) feedback High Low (-) feedback Low High 1:1 Developmental Trends Biomass P:R Ratio Primary productivity Respiration Time Nutrient Loss Years 48 16

17 General trends (continued) Early Late Structural Attributes Food chains Linear, grazing Web like, detrital Niche specialization Low High Organism size Small Large Biochemical diversity Low High Species diversity * * Functional Attributes Solar energy trapped Low High GPP/Biomass High Low Reproductive strategy r-selected k-selected Importance of chance High Low Stability *Low *High Limiting factors Time *depends on system and how/what is measured! (modified from Odum 1969) 49 Structural change: species diversity Trend differs for different groups E.g. Chance Creek and Clark Farm sites (climax = beech-maple, oakhickory) Tree diversity will decrease, understory diversity will likely increase E.g. Glacier Bay (climax = hemlock) Tree and tall shrub diversity peak at mid-stage Overall Plant Species Diversity (Reiners et al. 1971) Plant Species Diversity by Group (Reiners et al. 1971) 50 Structural change: species diversity Animal diversity often follows plants E.g. Piedmont Plateau (Climax = oak-hickory) Plant Species Diversity (Oosting 1942) Bird Species Diversity (Johnston and Odum 1956) But some animals favor or require early successional communities 51 17

18 Rate of change is a function of organism size 52 e.g. Metabolic patterns in forests and aquatic microcosms Development in forest and in aquatic microcosm (Odum 1971) Prod, Resp, Biomass 52 Functional change: Biomass accumulation model 53 4 phases of ecosystem development in Hubbard Brook following major disturbance 1. Reorganization (0 20 years) Plant biomass Total ecosystem biomass & available nutrients 2. Aggradation ( years) Total biomass 3. Transition Total biomass 4. Mosaic steady-state Biomass fluctuates around a mean Biomass Accumulation Model (Bormann and Likens 1981) 53 Hubbard Brook Experimental Forest

19 Hubbard Brook Experimental Forest