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BIOL2010
Module 3
| Question | Answer |
|---|---|
| What is an ecosystem? | The fundamental concept appropriate to the biome considered together with all the effective inorganic factors of its environment. |
| What are autotrophs? | Organisms with the ability to use carbon and energy to produce complex organic compounds (e.g. carbohydrates, fats, proteins) |
| Primary productivity | rate of primary production; measures carbon fixation relative to space and time; measured as g/m^2/year |
| Gross primary production (GPP) | total amount of carbon fixed by autotrophs in the ecosystem; photosynthetic drawdown of carbon dioxide; in most ecosystems, it depends on the photosynthetic rate of autotrophs |
| Leaf Area index (LAI) | the amount of leaf area measured per area of ground; describing how much photosynthesis is possible in an ecosystem; differs in different biomes |
| Net Primary Production (NPP) | the amount of energy captured by autotrophs that results in an increase in biomass (new tissue growth in plants); GPP - respiration |
| What influences NPP? | rainfall and temperature |
| How is NPP influenced by rainfall? | initially, NPP increases with precipitation but only to a point (more rainfall generally means more plant growth); with very high rainfall, there is heavy cloud cover year round, resulting in less light and plant growth |
| NPP influenced by rainfall pt.2 | significant rainfall can also cause nutrient leaching from soils, leading to growth being nutrient limited; wet soils can become saturated which gives rise to low oxygen levels in the soil which can limit root function, limiting NPP |
| How is NPP influenced by temperature? | NPP increases with average annual temperature up to a point (chemical reactions and hence plant growth are faster and easier at warmer temperatures); high variation in this relationship as there are interacting factors (e.g. rainfall) |
| NPP influenced by temp pt.2 | although NPP scales with average temperature, this does not mean that ecosystem carbon storage will as well; warmer temps increase respiration rates and loss of carbon; even if NPP is high the net ecosystem exchange (NEE) may not scale with it |
| How is oceanic NPP produced? | phytoplankton perform most of the primary production; primary producer biomass in ocean at any given time relative to NPP is low compared to terrestrial ecosystems (small, rapidly growing organisms); seaweed, kelp, mangroves also contribute to NPP |
| Variation in NPP | can be a good preliminary indication of ecosystem health and it is strongly associated with the global carbon cycle |
| Normalised difference vegetation index (NDVI) | used in larger areas like rainforests; focus on chlorophyll concentrations as a proxy for GPP and NPP ('greenness'); chlorophyll concentrations can be estimated using remote sensing methods that rely on reflection of solar radiation from primary producers |
| NDVI | formula = (NIR - red)/(NIR + red); where NIR = amount of near infra-red wavelengths, red = amount of red wavelengths; vegetation has HIGH NDVI values, soil and water have LOW values |
| Net ecosystem exchange (NEE) | NEE = GPP - (AR + HR); where AR = autotrophic respiration, HR = heterotrophic respiration; the more encompassing estimate of the amount of energy available for transfer and use in an entire ecosystem |
| Succession and NPP | NPP changes through succession; highest NPP usually during intermediate stage (plant diversity and nutrient supply highest); in old-growth forests, NPP may decline with decreasing LAI and photosynthetic rates |
| Trophic levels | the ecological roles of organisms in an ecosystem are dtermined by their trophic interactions which determine how energy and nutrients move through an ecosystem |
| Limitations of food webs | note all organisms conveniently confined themselves to an 'assigned' trophic level; the number of organisms and interactions to identify, qualify and quantify is massive; not metamorphosis; static description of energy flow; no migration |
| Detritus | dead particulate organic matter; in terrestrial systems detritus present in leaf litter and other organic matter intermixed with soil (soil organic matter); in aquatic systems, organic material suspended in water and accumulates on sea floor (marine snow) |
| Detritus in terrestrial systems | only a small portion of biomass is consumed due to land plants not being mostly consumable (woody lignin) means that most of the energy flow passes through detritus |
| Allochthonous energy inputs | external energy inputs from outside the ecosystem |
| Autochthonous energy inputs | energy produced by autotrophs within the ecosystem |
| Aquatic systems energy inputs | autochthonous input is from photosynthesis of large plants and algae in shallow waters and phytoplankton in open water; allochthonous input provided by rivers via groundwater or wind |
| Terrestrial biomass and energy pyramids | primary producers have most biomass and energy whereas secondary carnivores have least biomass and energy |
| Aquatic biomass and energy pyramids | can sometimes be inverted (mainly in open ocean); little biomass or primary producer and large amount of predator biomass; energy is biggest at primary level and smallest at top; inverted pyramids more common in low productivity areas |
| 3 hypotheses that explain available edible biomass | 1. top-down population regulation 2. autotroph defences against herbivory 3. phytoplankton are more nutritious for herbivores than terrestrial plants |
| Hypothesis 1 | herbivore populations are constrained by predators and never reach carrying capacity; predator-removal experiments in some ecosystems support this |
| Hypothesis 2 | plants of resource-poor environments tend to have stronger defences than plants from resource-rich environments |
| Hypothesis 3 | terrestrial plants have structural components (wood) with few nutrients; carbon to nutrient ratio is an indicator of food qaulity; phytoplankton have carbon to nutrient ratio closer to those of herbivores than of terrestrial plants |
| Trophic efficiency | a measure of how energy transfers between trophic levels; incorporates 3 types of efficiency: consumption, assimilation and production efficiency |
| Consumption efficiency | proportion of available energy that is ingested; higher in aquatic than terrestrial ecosystems; higher usually for carnivores than for herbivores |
| Assimilation efficiency | proportion of ingested energy that is assimilated (digested); determined by both food quality and the physiology of the consume; plants and detritus have lower food quality (low N & P), animals are higher quality; endotherms higher assimilation efficiency |
| Production efficiency | proportion of assimilated food that goes into new consumer biomass; body size affects heat loss in endotherms (SA:V ratio decreases with increased body size, larger endotherms have higher production efficiency |
| Trophic cascades types of control | bottom-up control; top-down control |
| Bottom-up control (trophic cascades) | suggests the things that limit net primary production are the plants themselves and the nutrients are available to them |
| Top-down control (trophic cascades) | suggests that energy movement is governed by the top predators, which then governs everything below; idea that plants aren't completely consumed because carnivores keeping herbivores in line |
| Trophic cascade | describing the resultant changes to the balance and energy transfer of an ecosystem that are caused by alterations to the abundance or biomass of a single trophic level or species |
| Limitations of food webs pt.2 | only feeding interactions, no pollination, symbiosis etc.; micro-organisms often ignored; often main focus of food webs is only those deemed most important for research and conservation |
| Food web uses | quantify importance of trophic connections by estimating interaction strength; identify keystone species and predict the impact of removing these from an ecosystem; predict how pollutants will bioaccumulate or biomagnify through the food web |
| Interaction strength | measure of the effect of one species on the population size or abundance of another species; can quantify it through removal experiments, observations, comparisons, predator/prey body size |
| Keystone species | those which have a greater (disproportional) influence than their abundance or biomass might predict; have important conservation implications |
| Bioaccumulation | where some chemicals are not metabolised or excreted by animals or plants and they become progressively more concentrated in tissues over an organism's lifetime |
| Biomagnification | when something else eats those affected oragnisms; occurs when concentration of toxic compounds increases in animals at higher trophic levels; animals at each level consume prey with higher and higher concentrations of the compounds |
| Nutrient requirements and makeup of organisms | all ecosystems have similar nutrient requirements, with some variation; organism's nutrient requirements related to its physiology, mode of energy acquisition, mobility, thermal physiology; C/N ratio of plants is much lower in animals than plants |
| Ideal C/N ratio | carbon is main component of plant structural compounds; nitrogen largely tied in enzymes; herbivores must ceat more food than carnivores to meet nutrient requirements |
| Where do plants get their nutrients from? | soil solution comprised of minerals from rocks, organic content from decomposing plant and micro-organisms, water |
| Rock formations on soils (Australia) | rock formations determine type of soil, which determines the plant community, flowing up through food web; Australia flora adapted to low nutrient concentrations due to soil type |
| Leaching during weathering of rock | nutrients at surface where rocks are released are leached out by water overtime; flow down soil profile creating different layers of soil; top=rich in organic matter; plants can acquire different nutrients if they send their roots to different levels |
| How does climate influence soil development (e.g. warm, wet conditions)? | soil development faster in these conditions as chemical reactions are faster with lots of water; tropical forest soils usually high rates of weathering and leaching and often nutrient-poor; most nutrients in them are in held above-ground biomass |
| How does climate influence soil development (e.g. higher latitudes)? | soils usually richer in mineral nutrients here; have seen periods of glaciation and de-glaciation which slowed the leaching process |
| Nitrogen fixation in plants | performed by bacteria that possess energetically expensive enzyme nitrogenase; trade-off in symbiosis is that the allocation of energy to N-fixation rather than growth reduces the competitive ability of plants for other resources |
| Nitrogen fixation in ocean | performed by cyanobacteria |
| What is decomposition? | process where detritivores break down detritus to obtain energy and nutrients; releases nutrients as simply, soluble organic and inorganic compounds that can be taken up by other organisms |
| How are decomposition rates influenced by the climate? | faster in wet and moist conditions, with soil moisture especially influencing the availability of water and O2 to micro-organisms; if soils too wet, low O2, inhibits detritivores; if soils too dry, low water, no micro-organism metabolism |
| How to achieve landscape ecology? | aerial photography; remote sensing from satellite images; Geographic Information Systems (GIS, enables storage and display of spatial data from different sources, can use it to produce layers of data to help understand pattersna dn what drives them) |
| Global Positioning Systems (GPS) in landscape ecology | can attach device to animals and track movements and migratory patterns (radiotelemetry); limitations: difficult to attach to small short-lived animals and small birds (can't fly) |
| What is landscape ecology? | concerned with spatial arrangement of landscape elemtns across Earth's surface; landscape elements might be any abiotic or biotic characteristic of a landscape that contributes to the habitat it defines |
| Landscape definition | an area in which at least one element is spatially heterogenous, and often can include multiple ecosystems |
| Heterogeneity definition | may refer to different types of landscape elements and their arrangement |
| Patches def | discrete areas of similar habitat within a larger landscape |
| Corridors definition | linear elements that connect patches |
| Matrix def | refers to the overall dominant landscape type |
| Mosaic def | a composite of heterogenous elements (patches, corridors, and matrix) that makes up the landscape |
| How to achieve biotic flow in landscape? | patches must be directly connected by corridors, or else the surrounding habitat (the matrix) must be suitable for dispersal |
| What affects landscape structure? | size of patches, aggregation/dispersal of patches, complexirty of patch shape, degree of fragmentation |
| Scale in landscape ecology | depends on the range and size of the organisms being studied; landscape may be heterogenous at a scale important to a beetle, but homogenous at a scale important to a kangaroo |
| What causes landscape patterns? | can be caused by physical forces (e.g. weather) but also by ecological processes (e.g. grazing); anthropogenic activities (agriculture, logging etc.) may affect current biodiversity and ecosystem processes, even after people have left (landscape legacies) |
| What is habitat loss and its causes? | the reduction of habitat available for species in a landscape; caused by human activities such as flooding, clearing, urbanisation, road-laying |
| What is fragmentation? | splitting of a landscape into smaller habitable patches; results in spatial isolation of population, making them vulnerable to the problems of small populations |
| What are edge effects? | biotic/abiotic changes associated with habitat boundary as it shrinks from habitat loss and fragmentation; the environment changes over a certain distance into the fragment; increase in fragmentation=increased amount of edges |
| What do habitat edges do? | can promote or deter dispersal (some species may benefit from foraging in one habitat and reproducing in another); invasive species especially often thrive at habitat edges |
| Characteristics of well-designed national parks and marine protected areas: | large size; fuse small reserves into larger ones; close proximity; connected by corridors (can reduce effects of fragmentation by preventing isolation of populations); circular (minimise edge effects relative to area); buffer zones (minimise edge effects) |
| What does a successful restoration require? | correct diagnosis of the ecological state of the area; accurate pre-determining of the restoration goals; application of ecological knowledge to recreate the desired type of ecosystem |
Created by:
tkeen40
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