Resumen tema 2 ECOSISTEMA

2.1.1 Distinguish between biotic and abiotic (physical)

components of an ecosystem.

• Biotic = Living. “A factor created by a living thing or any living component within an environment in which the action of the organism affects the life of another organism, for example a predator consuming its prey.” (from www.biology-online.org)

◦ Flora = plants

◦ Fauna = animals ◦ Predation = hunting

◦ Interspecies competition = different species competing for the same resources

◦ Intraspecies competition = members of the same species competing for the same resouces

•

Abiotic = non-living. “A non-living chemical or physical factor in the environment, such as soil, pH, forest fire, etc.” (www.biology-online.org)

•

Edaphic factors: geology

◦

Soil composition & nature -

■

sand/silt/clay/OM content influences availability of water and nutrients for plant life

■

Salinity & pH also influence nutrient availability

■

Type of bedrock determines mineral content in soils

■

Aeration/compaction - particle spacing within soil makes water & air more or less available to plants and micro-organisms living in the soil

◦

Topography - slope influences erosion, runoff, & soils’ ability to hold water

•

Climatic factors - Light, temperature, humidity, precipitation

•

Social factors - land and resource use

◦

Agriculture

◦

Large-scale forestry

◦

Urbanization

◦

Industry

2.1.2 Define the term trophic level.

2.1.3 Identify and explain trophic levels in food chains and

food webs selected from the local environment.

◦

Autotrophs = producers. “self-feeders” make their own food via photosynthesis

◦

Heterotrophs = consumers. Must get energy and nutrients from other living organisms.

◦

Primary consumers - herbivores eat only plant material

◦

Secondary consumers - omnivores eat primary consumers and producers

◦

Tertiary consumers - mostly carnivores that eat other consumers

◦

Quaternary consumers - top of the food chain carnivores, the big hunters

◦

Decomposers - obtain nutrients by breaking down dead organic matter

◦

Detritivores - obtain nutrients by breaking down decomposing matter

2.1.4 Explain the principles of pyramids of numbers,

pyramids of biomass, and pyramids of productivity, and

construct such pyramids from given data.

2.1.5 Discuss how the pyramid structure affects the

functioning of an ecosystem.

Ecological pyramids -

Graphic models showing differences in living matter at each trophic level in an ecosystem

•

Pyramids of numbers:

◦ show how many organisms at each trophic level

◦ base level (producers) usually greatest in number

◦ top level is least

◦ snapshot in time

• Pyramid of biomass:

◦ shows the total dry biomass at each trophic level

◦ must kill the organism to measure its dry biomass, so not practical or ethical to measure all the biomass at a trophic level

◦ snapshot in time

• Pyramid of productivity:

◦ energy being generated or available as food at each trophic level

◦ shows flow of energy over time among trophic levels

Source: Rutherford, Jill. Environmental Systems and Societies Course Companion. Oxford University Press. Oxford. 2009.

2.1.6 Define the terms species, population, habitat, niche,

community and ecosystem with reference to local examples.

◦ An individual belonging to a group of organisms (or the entire group itself) having common characteristics and (usually) are capable of mating with one another. (source: www.biology-online.org)

◦ taxonomic group whose members can interbreed (source: wordnetweb.princeton.edu/perl/webwn)

• Population:

◦ A group of organisms of one species that interbreed and live in the same place at the same time (e.g. deer population). (source: biology-online.org)

◦ A group of individuals of one species, which live in a particular area and are much more likely to breed with one another than with individuals from another such group. (source: symposia.cbc.amnh.org/archives/seascapes/glossary.html)

• Habitat:

◦ the type of environment in which an organism or group normally lives or occurs (source: wordnetweb.princeton.edu/perl/webwn)

◦ The home to a particular organism where the species will attempt to be as adaptive as possible to that particular environment. (source: biology-online.org)

• Niche:

◦ The role or functional position of a species within the community of an ecosystem.

(Source: www.sdnhm.org/exhibits/mystery/fg_glossary.html)

◦ The interrelationship of a species with all the biotic and abiotic factors affecting it. (source: biology-online.org)

• Community:

◦ a group of interdependent organisms inhabiting the same region and interacting with each other

(source: wordnetweb.princeton.edu/perl/webwn)

◦ The organisms living in a community interact with one another, often, affecting each other’s abundance, distribution, adaptation, and existence. An ecological community may range in size from the very small community as in a pond or a tree to the huge regional or global community as in a biome. (source: biology-online.org)

• Ecosystem:

◦ A system that includes all living organisms (biotic factors) in an area as well as its physical environment (abiotic factors) functioning together as a unit. (source: biology-online.org)

◦ a dynamic complex of plant, animal and micro-organism communities and their non-living environment, interacting as a functional unit, [applicable on a variety of scales].

(source: citizenship.yara.com/en/resources/glossary/index.html

Bioaccumulation - a chemical or substance which does not break down (or breaks down slowly) in an organism's body will accumulate over time as that organism ingests more and more of the substance

Biomagnification - concentrations of slowly-decomposing substances increase with each higher trophic level

• Producer absorbs small amount of substance

• 1st consumer eats many producers & absorbs substance from each one = higher concentration

• 2nd consumer eats many 1st consumers & absorbs substance from each = still higher conc.

• 3rd consumer eats many 2nd consumers & absorbs substance from each = even higher conc.

• 4th consumer...pattern continues up the food chain/web with highest concentrations at top

Mutualism - interaction between species which are mutually beneficial (i.e. both gain something positive from the interaction and neither suffers)

• a.k.a. symbiotic relationship

◦ Examples of symbiotic relationships:

■ Lichens are a combination of a fungus and either algae or cyanobacteria (photosynthetic bacteria). They exchange sugars, minerals, and water. ■ Nitrogen-fixing plants (family Leguminocae) and the Rhizobium

bacterium on their roots. The plant provides sugars, while the bacteria 'fix' atmospheric nitrogen in a form that the plant can use to build its biomass.

■ Mycorrhizal fungi grow on many tree roots. The fungi absorb phosphates from the soil and increase the surface area of the roots, which means the tree gains phosphates for growth and is also able to absorb more water and minerals from the surrounding soil.

• parasitism (below)

• commensalism, in which one organism gains something, while the other is either not harmed at all or not significantly harmed. In a commensal relationship, one organism distinctly gains something at a cost, however small, to the other organism.

◦ Examples of commensalism:

■ Heartworms live in the right side of dogs' hearts ingesting protein and nutrients from the blood; if the population of heartworms grows too quickly, they can clog the dog's heart and kill it, destroying the heartworms' colony

the whale leaves behind or drops. (Source: http://www.cbu.edu/~seisen/ ExamplesOfCommensalism.htm)

Parasitism - a form of mutualism in which one organism lives in or on another.

• Generally speaking, parasites don't kill their hosts because they need the host in order to survive; without a living host, the parasite will also die.

• Examples:

◦ tapeworms live in another organism's digestive tract and feed on the digested material

◦ fleas, ticks, and mosquitoes ingesting protein from the blood of their hosts Predation - simply put: hunting.

• A predator kills and eats prey.

• Predation is not limited to animals eating animals! There are carnivorous plants that capture and digest animals:

• Examples of predation:

◦ most of the interactions you've seen in the Tanzanian savanna (lions/zebras, cheetahs/antelope, etc) too many to list

◦ Venus flytraps (Dionaea muscipula) capture insects, arachnids, and occasionally small amphibians and rodents

◦ Pitcher plants (Genus Nepenthes) have specialized leaves which hold water and digestive juices and are covered in a slippery surface so that whatever falls into the pitcher cannot climb out

◦ Bladderworts (Genus Utricularia) like the Venus flytrap use trigger hairs to campture microbes or other small organisms

◦ Sundews (Genus Drosera) produce sweet-smelling and very sticky nectar. When insects try to eat the nectar, they stick to the sundew and are digested by it. (Source:http://www.sarracenia.com/faq/faq5240.html)

• Sir David Attenborough is one of my heroes. Check out this video of his about carnivorous plants (From "The Secret Life of Plants" via YouTube)

Herbivory - just like predation, except that the predator kills and eats plants instead of animals. All grazing animals (cows, goats, sheep, buffalo, antelope, zebras to name a few) practice herbivory.

Competition - different organisms compete against one another for limited resources.

• Intraspecific competition (competition within members of the same species) tends to limit the population of that species within an ecosystem.

• Interspecific competition (between different species) can result in shared resources and relatively balanced populations of both species, OR one species can out-compete the other and remove the weaker species from the ecosystem. This is called competitive exclusion.

2.2.1 List the significant abiotic (physical) factors of an

ecosystem.

2.2.2 Describe and evaluate methods for measuring at least

three abiotic (physical) factors within an ecosystem.

Assignment: Measuring Abiotic Factors at IST - Practical Write-up assessed under DCP. Click

here for the complete description and instructions.

Read pp.306-309 in the IB ESS Course Companion before studying the notes below!

There's a wide variety of abiotic factors that influence what may live in an ecosystem, some examples of which are listed below:

Marine ecosystems:

• salinity - many marine organisms tolerate a variety of salt concentration levels in the water, which can be checked with a few tools:

◦ hydrometer measures specific gravity or density of a sample (relative weight of 1.0L salt water compared to 1.0L pure fresh water)

◦ refractometer measures differences in light refraction between the saltwater sample and a freshwater control

•

pH - use a pH meter (available in the IST science building). The pH of saltwater is naturally higher (i.e. more alkaline) than that of fresh water. According to several marine

aquarium websites, a pH of 8.2 is ideal for saltwater fish.

•

temperature - every organism has an optimal temperature range in which it thrives. An organism may be able to survive at warmer or cooler temperatures, but it will do so under stress, which requires more energy (and therefore food), and decreases its' ability to compete for other resources within the ecosystem. This is particularly important for

ectothermic (cold-blooded) organisms, which are a majority of marine animals. A change in temperature can also influence the pH of water.

•

dissolved oxygen (DO) - the amount of oxygen available for marine organisms, like terrestrial organisms, determines which organisms can survive in a particular location. DO levels fall with increased temperature and organic compounds from either sewage, agriculture, or industry. DO can range from 0-18 ppm, but most healthy ecosystems have a DO level of 5-6

ppm(http://www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/do/). Measuring DO can be tricky and labor-intensive, requiring either a complicated Winkler titration or oxygen-selective electrodes.

•

wave action - waves carry energy; thus, larger and prolonged waves can move larger particles, thereby 'mixing' water, oxygen, and sediment more. Areas with a lot of wave action tend to have higher DO levels. Waves can also increase the turbidity of the water and determine the nature of a coast line - i.e. sandy vs rocky.

(http://www.pals.iastate.edu/agron154/Agron_154/Unit_7/terms.htm) Freshwater ecosystems:

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turbidity - "A cloudy condition in water due to suspended silt or organic

matter."(www.groundwater.org/gi/gwglossary.html) Cloudy = high turbidity and clear = low turbidity. According to Wikipedia (I know, I know...)

←

"Turbidity in lakes, reservoirs, channels, and the ocean can be measured using a Secchi disk. This black and white disk is lowered into the water until it can no longer be seen; the depth (Secchi depth) is then recorded as a measure of the transparency of the water (inversely related to turbidity). The Secchi disk has the advantages of integrating turbidity over depth (where variable turbidity layers are present), being quick and easy to use, and inexpensive."

←

flow velocity - the rate at which water moves through a specified area in a given amount of time. Some aquatic organisms prefer high flow velocity (fast water) while others thrive at lower flow velocities. The simplest way is to time how long a partially-submerged object takes to travel a certain distance. For an explanation of how to more precisely measure stream flow, visit this site from the USGS describing the method - it's complicated!

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temperature - see notes above

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dissolved oxygen - see notes above Terrestrial ecosystems

•

temperature - depends on insolation (incoming sunlight), wind & ventilation, latitude, color and texture of the surface. Measure temperature with liquid thermometers or datalogging

•

light intensity - influences photosynthesis rates as well as body temperature of ectotherms (cold-blooded animals). Light intensity is highly variable with weather conditions, season, time of day, and surrounding terrain & vegetation cover. It can be measured with light meters available from photography stores or the IST science department.

•

wind speed - wind carries sediment and acts as a dessicating (drying) force in

ecosystems, increasing evaporation and transpiration rates. Wind speed is measured with a few different tools:

◦

anemometer: spinning cups on a permanent or hand-held post. The number of revolutions per time period can be converted to a wind velocity.

◦

Ventimeters use differences in air pressure to determine the velocity of wind passing over the open end of a tube.

◦

Beaufort scale of wind speed from 0 to 12. The table below describes it better than I can. Image source:

(http://media.graytvinc.com/images/beaufort_scale_tbp.gif) • particle size - influences how well a soil holds water as well as its cation exchange

capacity (CEC) - the mechanism by which nutrients are swapped between the physical soil matrix and the organisms living in the soil. Soils with large average particle sizes (such as boulders, pebbles, and sand) drain more quickly and hold fewer cations than soils with small particles (silt and clay). Seiving through different size screens is the most frequently used method to determine particle sizes.

• slope - steep slopes drain water rapidly and dry out quickly, have thinner soil layers, and tend to have lower levels of organic matter (OM) than more gently-sloping areas. Steep slopes also erode faster than gentle slopes. Slope can be measured with a clinometer, a field level, or calculated as a % (rise/run).

• soil moisture - influenced by particle size and climatic factors. The easiest way to measure soil moisture is to measure the mass of a sample, then dry it for several days until its mass is constant. The difference in the two masses is the mass of the water evaporated from the sample.

• drainage - influenced by slope and particle size

◦

internal drainage: how rapidly water percolates down through soil layers

◦

external drainage: how rapidly water moves across the landscape

water, and living organisms. Mineral content is usually measured by burning off all the living material in a sample at very high temperatures.

Questions to consider for the end-of-term exam OR the IB ESS exam in May 2011:

←How might each of these factors vary in a given ecosystem with depth? At different times of day? At different distances? During different seasons?

←Outline and evaluate a method for measuring one of the abiotic factors listed above.

2.3.1 Construct simple keys and use published keys for the identification of organisms.

Read pp.309-312 in the IBO ESS Course Companion.

In class, develop a dichotomous key for all the organisms listed in Figure 16.4: "A picture key of pond animals". Your key should start with the largest groups of organisms and split them into successively smaller groups until each organism is alone in its own group. No characteristic should be used twice to subdivide different groups.

2.3.2 Describe and evaluate methods for estimating abundance of organisms.

Because it's usually impractical to sample every single organism in an ecosystem, we use statistical sampling to estimate the abundance of species within the ecosystem.

A transect is a line across an ecosystem along which quadrats may be placed for sampling. Quadrats are square frames of a specific size, in which we count the number of each species of organism.

• The size of the quadrat depends on the size of organism anticipated (i.e. small quadrats for small organisms and large quadrats for large organisms).

• The number of quadrats used for sampling depends on the number of species found. If we plot the number of species found against the number of quadrats used, once the number of species is stable, it's no longer necessary to add more quadrats - we can assume we've found all the species in the sample area. Refer to Fig. 16.6 on p.315 of the IBO ESS Course Companion.

• Placing quadrats: Quadrats can be placed randomly, continuously, or systematically.

◦ Random quadrats - use random number tables (easily generated online) to determine placement of quadrats. Click here for an example of how to

do this.

◦ Continual quadrats - place quadrats adjacently along a transect line and every species along the line. This is quite accurate but can be extremely time-consuming.

◦ Systematic quadrats - place quadrats along a transect at regular, pre-determined intervals.

Estimating abundance depends on the type of organism being sampled.

•

Plants are stationary, so we can use the percentage cover to estimate their

abundance. Simply put, estimate the % of each quadrat covered by each species' leaf area. The total % in a quadrat do NOT have to total 100%!

•

We can also count the density of individuals - how many per square meter.

•

Frequency of individuals is the % of the number of quadrats where a particular species is found (i.e. Acacia senegalensis was present in 47 of 92 quadrats, for a frequency of 51%).

Here's a Youtube video podcast showing how an AP Environmental Science class in North Carolina uses some of these field sampling techniques.

Capture, mark, release, recapture: Animals within an ecosystem are caught and marked so that they may be tracked in the future, then released back into their habitat. At a

the field notes. We must be careful to make sure that the way the animals are marked doesn't make them more prone to be killed and eaten by predators or harm their chances of survival in any other way (i.e. making it more difficult to hunt or find food for themselves).

The Lincoln Index is an important tool for estimating population size via capture-release programs. This method is frequently used but is not perfect. See some of the assumptions on p.317 of the IBO ESS Course Companion for further explanations. In class, compelte the

Lincoln Index calculations on p.317. The formula for calculating the Lincoln index is explained below:

N = (n1 x n2)/m2 where:

←

N = total population

←

n1 = number of animals first marked and released

←

n2 = number of animals captured in the second sample

←

m2 = number of marked animals in the second population

2.3.3 Describe and evaluate methods for estimating the biomass of trophic levels in a community.

Biomass, as the name implies, is a measurement of the mass of living material at a trophic level or within an ecosystem. Because water is NOT living, we do not include it in our

calculations.

Since all organisms are made of roughly the same organic molecules in similar proportions, a measure of their dry weight is a rough measure of the energy they contain. Therefore, material brought into the lab must be dried completely before measuring its mass. Normally, this is accomplished by placing the material in a warm - not hot - drying oven and allowing it to dry completely over a day or two before weighing it.

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Use the Lincoln index (above) to estimate the total population of a secies of organisms.

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Once the mass of an average organism within the population is known, that mass can be multiplied by the estimated population to determine the total biomass of the

population of that species.

←

This process is repeated until all species at a trophic level have been accounted for.

←

(Source:

2.3.4 Define the term diversity.

Diversity (commonly 'biodiversity' when discussing ecological principles) is a measure of the relative abundance of different living organisms within an ecosystem. Diversity is not simply the number of different species found in an ecosystem - consideration must be given to the relative abundance of all species within the system.

Two ecosystems may have the same number of species (called 'species richness'), but vary considerably in their diversity. If one or two species make up most of the total number of living organisms within the system, that system is considered less diverse than one in which the numbers of every species are relatively similar (called 'species evenness').

Look at the example on p.318 (recreated below). Both ecosystem 1 and ecosystem 2 have the same species richness - they each contain 3 different species. They also have similar numbers of organisms (70 and 72, respectively). However, the vast majority of organisms in ecosystem 2 are from a single species - species 'A'. Because the distribution of species in ecosystem 2 is skewed heavily to species A, ecosystem 2 is considered less diverse than ecosystem 1. How does Ecosystem # 3 compare to #1 and #2 in terms of species richness and species evenness?

Diversity of different ecosystems

Species # of Individuals

Ecosystem #1

A 25

B 24

C 21

Ecosystem #2

A 65

B 3

C 4

Ecosystem #3

A 28

B 32

C 12

2.3.5 Apply Simpson’s diversity index and outline its significance.

Simpson's diversity index is a mathematical model used to compare the relative biodiversity of different ecosystems. A full explanation can be found on p.318 of the IBO ESS Course

Companion. In short, the higher the numerical value of Simpson's diversity index, the greater the biodiversity of a system.

D = [N*(N-1)]/[Σ(n*(n-1)]

Where...

←

D = diversity index

←

N = total number of organisms of all species found

←

n = number of individuals of a particular species

Complete the "To do" activities # 1-3 on p.318 in class. In addition, respond to the following prompts in your notebook:

←

Calculate the diversity index 'D' for a sample from ecosystem #3, the North American temperate deciduous forest. Sample data are listed in Table 1, below.

←

What would happen to 'D' if all the oaks were harvested, leading to a 40% decline in the squirrel population, a decline of 25% in the woodpecker population, and a 30% decline in the warbler population in ecosystem #3?

Table 1: Species distribution in the eastern deciduous forest of North America, October

2009.

Species # of individuals per species

Red oak (Quercus rubrum) 55

Silver maple (Acer saccharinum) 60

Eastern white pine (Pinus strobus) 32

Eastern white-tail deer (Odocoileus

virginianus)

Species # of individuals per species

Eastern grey squirrel (Sciurus carolinensis) 110

Red bellied woodpecker (Melanerpes

carolinus)

50

Yellow-rumped warbler (Dendroica

coronata)

42

This site has a good step-by-step explanation of Simpson's Diversity Index.

2.4.1 Define the term biome.

2.4.2 Explain the distribution, structure and relative

productivity of tropical rainforests, deserts, tundra and any

other biome.

Here's a list of some useful websites covering all the major biomes and their distribution across the globe:

• The World's Biomes - University of California Museum of Paleontology

• World Biomes - BluePlanetBiomes.org

• Biomes of the World - Missouri Botanical Garden

• Biomes of the World - TheWildClassroom.com

• World Biomes - WorldBiomes.com

• Marietta College Department of Biology and Environmental Science Biomes Main Page

Biome: Here are some definitions I found on the web.

←A major ecological community or complex of communities, extending over a large geographical area and characterized by a dominant type of vegetation.

(http://www.biobasics.gc.ca/english/View.asp?mid=411&x=696) ←A major ecological community, classified according to the predominant vegetation and

characterized by adaptations of organisms to that particular environment. (www.conservation.org/resources/glossary/Pages/b.aspx)

←a regional ecosystem characterized by distinct types of vegetation, animals, and microbes that have developed under specific soil and climatic conditions.

•

Distribution:

◦

tropical climate zone (duh!)

◦

4 main areas

-■

Amazon basin in South America = 45.0%

■

Congo River basin in central Africa = 30.0%

■

Indomalayan or Asian rainforest = 16.0%

■

Australasian zone = 9.0%

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Structure:

←

at least 2 000 mm precipitation per year

←

stable temperatures (generally 22-34 Celsius)

←

12 hours of daylight year-round

←

Complex vertical layering produces separate but overlapping zones within the forest

←

Food webs are intricately interwoven and interdependent

←

poor quality soils (low nutrients) because nutrients are contained in the tree biomass

←

Relative productivity:

← Extremely high productivity due to year-round photosynthesis, stable temperature and precipitation.

← Biomass is concentrated in woody tissue of trees (i.e. most of the biomass in the rainforest is in the producers)

←

References:

←

http://rainforests.mongabay.com

Deserts

←Distribution:

← tropical and temperate climate zones

← Hot deserts:

← Africa (Sahara in the north, Namib and Kalahari in the south)

← Arabian peninsula

← Australia

← Temperate deserts:

← Central Asia (Gobi in Mongolia and China)

← western USA (Sonora)

← Coastal deserts:

← west coast of South America (Atacama in Chile and Peru)

• Structure:

◦ evaporation exceeds precipitation - that's why they're dry!

◦ average temperature 20-25 Celsius (includes both night and day) but will reach extremes of both hot and cold 12 - 49 Celsius

◦ drought-tolerant plant species

◦ rodents and other small mammals, insects, reptiles, & birds are predominant fauna

• Relative productivity

◦ low productivity

• References:

◦ University of Edinburgh, Scotland - desert biome ◦ Biology Pages at Ultranet by J. Kimball

◦ Energy Flow and Community Structure in Deserts - Earlam University ◦ University of California Museum of Paleontology - desert biome Tundra

• Distribution:

◦ polar climate zone

◦ northern hemisphere ONLY (no land in corresponding latitudes of southern hemisphere)

◦ Alaska, Canada, Scandinavia, Russia

• Structure:

◦ frozen ground (permafrost) prevents deep root penetration

◦ low nutrient content in soil due to minimal biological activity during long winters

◦ short plants due to frozen ground and nutrient shortage

◦ windy!

◦ lichens, mosses, and heaths - no trees

◦ mammals predominate; no reptiles or amphibians due to cold climate

• Relative productivity:

← low productivity

←References:

← Marietta College Tundra page

← Biology Pages at Ultranet by J. Kimball

Taiga (northern coniferous forest)

• Distribution:

◦ polar climate zone

◦ Alaska, Canada, northern Europe and northern Asia

◦ south of the tundra biome

←Structure:

← harsh, long, cold winters; relatively cool summers

← long nights (winter) long days (summer)

← precipitation falls throughout the year - snow melt provides much water for flora

← dominant vegitation is coniferous trees (Fir, spruce, pine species), mosses, grasses, & lichens

← acidic soil from evergreen needles

←Relative productivity:

← relatively low, but large insect and bird migrations with seasons

← rodents and mammals dominate fauna

← low diversity

←References:

← ICSU Scope 56 - Coniferous Forests, Grasslands, and Savanna ← Biology Pages at Ultranet by J. Kimball

← Wikipedia Taiga page

Temperate deciduous forest

• Distribution:

◦ temperate climate zone

◦ eastern North America, western Europe, China, Korea, Japan, Australia

• Structure:

◦ precipitation falls throughout the year

◦ distinct summer and winter seasons with fluctuations in temperature and day length

◦ layers within the forest - large trees, small understory trees, shrubs, ground zone

• Relative productivity:

◦ high - 2nd highest after tropical rainforest

◦ well-developed food webs

◦ productivity fluctuates with seasons

• References:

◦ Biology Pages at Ultranet by J. Kimball

◦ Mariette College Temperate forest page

Prairies (temperate grasslands)

• Distribution:

◦ temperate climate zone

◦ north America (plains states), south America (Argentina), Africa (Zimbabwe), central Asia

• Structure:

◦ less than 10% tree cover

◦ dominant vegetation is grasses

◦ deep, rich, high-quality soil with lots of nutrients

◦ humid; seasonal precipitation

• Relative productivity:

◦ relatively high

◦ high fauna diversity due to large amount of producers supporting extensive food webs - lots of grazing animals

• References:

Savannas

• Distribution:

◦ tropical climate zone

◦ Africa, South America, India, Australia, parts of SE Asia (Burma, Thailand)

• Structure:

◦ 235 - 1 000 mm precipitation annually

◦ distinct wet and dry seasons with long periods of drought

◦ scattered shrubs and isolated trees

◦ warm throughout the year

◦ plants adapted for drought

◦ animals adapted for running (long legs, good eyesight)

• Relativeproductivity:

◦ relatively high - grasses and shrubs provide ample food for well-developed food webs

• References:

◦ ICSU Scope 56 - Coniferous Forests, Grasslands, and Savanna ◦ Encyclopedia Brittanica

◦ PlantzAfrica.com

◦ BluePlanetBiomes.org

Chaparral (Scrub forest)

• Distribution:

◦ temperate climate zone

◦ northern California, coastal zones surrounding Mediterranean Sea, central Chile, western and southern Australia

• Structure:

◦ 300 - 1 000 mm precipitation annually

◦ mild wet winters, hot dry summers

◦ stable temperatures year-round

◦ soil is thin, poor quality, rocky, and usually steep

◦ prone to wildfires

◦ plants adapted to drought

• Relative productivity:

◦ dense populations of trees and shrubs

◦ medium-to-low productivity restricted by poor soil and seasonal precipitation

◦ fauna is mostly small mammals, birds, and insects; not many large animals

• References:

◦ Biology Pages at Ultranet by J. Kimball

◦ Wikipedia chaparral page

Coral reefs

• Distribution:

◦ eastern coasts of Australia, Africa, central America, Oceania (Malaysia, Indonesia)

• Structure:

◦ warm, shallow water (less than 25 m) because sunlight required for photosynthesis

◦ algae and phytoplankton form foundation of coral reef food chain

◦ densely populated with corals and fish (fauna)

◦ salinity levels also dictate location

◦ wave action provides oxygen and helps clean the reef

• Relative productivity:

◦ high - very diverse; compared to "rainforests of the sea"

• References:

◦ Texas A&M University coral reef page

Estuaries

• Distribution:

• Structure:

• Relative productivity:

• References: Lakes & Rivers

• Distribution:

• Structure:

• Relative productivity:

2.5.1 Explain the role of producers, consumers

and decomposers in the ecosystem.

2.5.2 Describe photosynthesis and respiration in

terms of inputs, outputs and energy

transformations.

Photosynthesis: 6CO

2

+ 6H

2

O --> C

6

H

12

O

6

+ 6O

2

•

inputs: light energy, water, carbon dioxide

•

outputs: oxygen gas, sugar (organic molecules)

•

energy transformations: light to chemical

•

respiration backwards!

←

inputs: oxygen gas, organic molecules (sugars)

←

outputs: carbon dioxide, energy in ATP, waste heat

←

energy transformations: chemical to heat

←

photosynthesis backwards!

2.5.3 Describe and explain the transfer and

transformation of energy as it flows through an

ecosystem.

Almost all energy enters Earth's ecosystems as solar insolation. That

energy is then transformed and used by the diverse variety of

organisms that make up food webs.

Through

photosynthesis

, producers transform sunlight (light energy)

into glucose (chemical energy), which they then use for

respiration

.

Chloroplasts

in plant cells use sunlight to convert CO

2

and water to

glucose (sugar) and O

2

gas. The plants' mitochondria then use the

sugars for energy to drive

respiration

(their cellular processes

required to stay alive).

Chlorophyll

is the pigment in chloroplasts that makes photosynthesis

possible by absorbing light from the sun. Red and blue wavelengths are

absorbed by the leaves and efficiently used in the energy

transformation process, but not the green wavelengths. The green

waves bounce off the leaf and reflect into our eyes, which is why leaves

look green!

2.5.4 Describe and explain the transfer and

2.5.5 Define the terms gross productivity, net

productivity, primary productivity and secondary

productivity.

productivity

•

the

rate

of growth (increase in biomass) in organisms

•

i.e. how slow/fast an organism increases its biomass

•

usually measured in g/m

2

_{/yr (for biomass) or kJ/m}

2

_{/yr (kJ =}

kiloJoules

, which is a measure of energy)

gross productivity (GP)

←

total gain in energy or biomass per unit area over time before

accounting for respiration or other energy/biomass losses

←

the amount of biomass that

could be accumulated

in a

measured area of an ecosystem in a given amount of time

←

does

not

factor in energy lost to respiration

←

usually measured in g/m

2

_/yr

←

difficult to measure because measurements must be taken in real

time as producers convert sunlight to sugar, which means they

must be killed, thereby stopping the process we're trying to

measure

net productivity (NP)

←

the actual amount of biomass accumulated after respiration has

been accounted for

←

remember that this must be

dry biomass

- water is not a part of

productivity

←

usually measured in g/m

2

_/yr

primary productivity (PP)

←

autotrophs are producers, and they are the 1st organisms in any

←

the biomass accumulated by autotrophs (plants, algae,

cyanobacteria)

←

usually measured in g/m

2

_/yr

secondary productivity (SP)

•

biomass accumulated by consumers (heterotrophs) in an ecosystem

•

usually measured in g/m

2

_/yr

2.5.6 Define the terms and calculate the values

of both gross primary productivity (GPP) and net

primary productivity (NPP) from given data.

gross primary productivity (GPP)

←

how fast autotrophs photosynthesize (convert sunlight to glucose)

←

some glucose is used to fuel the autotrophs' life processes: growth,

respiration, homeostasis

←

usually measured in g/m

2

_{, but very difficult to measure}

net primary productivity (NPP)

•

the amount of biomass accumulated by autotrophs after respiration

•

think of NPP as the food available to consumers within the

ecosystem

•

usually measured in g/m

2

2.5.7 Define the terms and calculate the values

of both gross secondary productivity (GSP) and

net secondary productivity (NSP) from given

data.

gross secondary productivity (GSP)

←

the amount of biomass absorbed (eaten) by consumers before any

←

includes food that is

egested

(excreted as waste) by the

consumer

net secondary productivity (NSP)

•

the actual change in biomass in an ecosystem during a given period

of time

•

accounts for energy lost to respiration and biomass lost through

egestion or other methods

•

usually measured in g/m

2

_{/yr (it's easier to measure biomass than}

energy)

To see calculations involving GPP, NPP, GSP, and NSP, see the review

activity in the orange box on p.43 of the IB ESS Course Companion.

2.6.1 Explain the concepts of limiting factors and carrying

capacity in the context of population growth.

A population is a species of organisms living in the same place at the same time. Organisms within a population interbreed and interact with one another and their physical environment throughout their lives.

There are 4 main factors controlling population sizes:

• natality - births increase the population

• mortality - deaths decrease the population

• immigration - movement of individuals into an area increases the population

• emigration - movement of individuals out of an area decreases the population Populations can theoretically grow to an infinite size, but available resources are finite, so individuals must compete for resources (remember intraspecific and interspecific competition!).

Carrying capacity (represented by a capital 'K') is defined as, "The maximum number of organisms, in a given species, that can use a given area of habitat without degrading the habitat and without causing stresses that result in the population being reduced."

(Source:www.desertmuseum.org/invaders/invaders_glossary.php)

Examples of limiting factors:

←disease ←parasites ←accidents ←disaster

←hunting & predation ←starvation

←competition for resources

←available oxygen and/or nutrients

Resources for exploring limiting factors and population dynamics:

•

Limiting Factors case study from Lake Winnipeg, Canada (PDF)

•

Limiting Facotrs in Wildlife Conservation from the International Hunters Education Association

•

Fundamentals of Populations and Population Growth

•

What is a Limiting Factor? from WiseGeek.com

2.6.2 Describe and explain S and J population curves.

Many populations are capable of growing at an exponential rate (exponential growth), such that a population of only 2 individuals doubles at a predictable rate

(2,4,8,16,32,64,128,256,512,1024,2048...).

Once the population's use of resources begins to outstrip the ecosystem's ability to replenish the resource, competition for those limited resources increases, and population growth slows due to environmental resistance - any factor that limits increases in the population.

Population growth is generally represented by 2 different curves: S-curves and J-curves.

S-curves

←

population grows exponentially at first, then growth slows as population #'s approach carrying capacity

←

results in a stable population

←

consistent with density-dependent limiting factors, described below Here is the classic s-curve (Source:

http://www.saburchill.com/IBbiology/chapters02/049.html)

←

rapid exponential growth quickly surpasses carrying capacity (called 'overshoot')

←

sudden collapse ('diebacks') brings population #'s below carrying capacity

←

population fluctuates over time

←

consistent with density-independent limiting factors, described below

Here's an example of a j-shaped population curve. What do you think this graph indicates about human population growth? What factors might have contributed to the relatively slow growth in human population prior to the 19th century? (Source:

http://www.tutorvista.com/content/biology/biology-iv/population/malthus-population-theory.php)

2.6.3 Describe the role of density-dependent and

density-independent factors, and internal and external

factors, in the regulation of populations.

Density-dependent limiting factors

←

depend on the size of the population

←

effects of the factors increase as the population grows

←

act as negative feedback

←

tend to be biotic

←

two categories of density-dependent factors:

←

internal factors - within a single species

←

limited food, space, or territory

←

reduced fertility rates

← external factors - between species

←

populations of predators or prey

←

diseases spread more easily in densely-populated areas Density-independent limiting factors

•

do NOT depend on the size of the population

•

tend to be abiotic

•

not part of a feedback system

•

effect the population regardless of its size

K-strategists

←populations stabilize at or near the carrying capacity of an ecosystem

←s-shaped curves

←good competitors

←adapted to stable ecosystems

←longer lives

←slower growth

←more 'parental' care of offspring gives each individual a better chance of surviving and reproducing

←higher proportion of offspring survive r-strategists

• populations overshoot carrying capacity, then collapse

• j-shaped curves

• adapted to disturbed sites and ecosystems

• shorter lives

• rapid growth to reproductive maturity

• reproduce rapidly

• produce many offspring with relatively high mortality rates so that at least some of the offspring survive to reproduce

• little or no 'parental' care of offspring because there are too many offspring to care for

2.6.5 Describe the concept and processes of succession in a

named habitat.

Succession - change in a community over time resulting in a stable climax community with complex interactions

Primary succession - also known as a prisere; succession that develops from bare rock. Primary succession is rare because almost all of Earth's surface has already undergone several stages of succession over the past 4.5 billion years

Sere - one in a series of communities at a particular location; they change over time in seral stages

←Hydrosere - primary succession in water

←xerosere - primary succession on dry land

←psammosere - primary succession on sand dunes

Seral stage - one step or phase in succession. There are several seral stages in primary succession:

-◦ 'soil' is almost exclusively mineral content with few microbes and/or organic matter

◦ nutrient-poor substrate

◦ limited water-holding capacity due to low OM content

◦ extremes of sun, temperature, and wind

• Colonization

-◦ pioneer species adapted to extreme conditions

◦ almost exclusively r-strategists

◦ simple soils develop from windblown dust and rock decomposition from lichens

◦ still harsh sun, wind, and temperatures

• Establishment

-◦ diversity increases as the number of producers able to live in the area increase

◦ soil microbes and invertebrates add OM and water-holding capacity

◦ weathering adds nutrients to soil

• Competition

-◦ larger plants create new microclimates

◦ diveristy increases due to new microclimates

◦ k-strategists begin to establish, outcompeting r-strategists for light, space, and nutrients

◦ microclimates make sun, temperatures, and wind less extreme

• Stabilization

-◦ fewer new species colonize because niches are already occupied ◦ food webs become more complex with more specialized niches ◦ specialized niches favor k-strategists

• Seral climax

-◦ stable and self-perpetuating community

◦ dynamic equilibrium of nutrient cycles

◦ patchwork of new/old growth maintains high levels of species diversit Secondary succession

-• succession on established soils

• early community was destroyed by natural causes (fire, flood) or human activity (farming)

• established soils support wider variety of seeds

• dormant seeds remain in soils from earlier community

• fewer seral stages due to already established soils

Pioneer community - first organisms to colonize bare rock; often lichens

Subclimax community

-←community present when movement through seral stages is interrupted by an abiotic or biotic factor

-• community of plants and animals which produces conditions favoring their own

perpetuation, and which will not undergo transition unless disturbed by external forces. (www.cabq.gov/aes/glossary.html)

• stable, in dynamic equilibrium Plagioclimax

-• the combination of plant species in an area brought about by human interference. Much of the European landscape is plagioclimax.

(www.tuition.com.hk/geography/p.htm)

• an area or habitat in which the influences of the human race, have prevented the ecosystem from developing further. (en.wikipedia.org/wiki/Plagioclimax) Zonation

-←different species occupying different spaces within a community or location based on a gradient of some biotic or abiotic factor

← different species of mangroves based on tidal movement

← different species of plants and animals where mature trees fall in a forest ← montane meadows surrounded by forest due to combinations of temperature,

wind, precipitation, and soil leaching

2.6.6 Explain the changes in energy flow, gross and net

productivity, diversity and mineral cycling in different stages

of succession.

Gross productivity

-• low during early stages of succession

◦ few producers

◦ limited or no soil to support rapid growth of new/more producers

←relatively high in later stages & climax communities

← more producers capable of growing once soil has developed Net productivity

-←relatively high during early stages

← the system is adding biomass

← energy lost to respiration is limited because population numbers are low

← P:R ratio is high

←falls during later stages

← established producer/consumer cycle means productivity & respiration are more balanced

← P:R ratio approaches 1:1 Biodiversity

◦ few producers adapted to bare rock

◦ few producers = no food source for consumers

• increases through later stages of succession

◦ food webs become more complex as number of producers increase

◦ specialized niches developing with high competition

◦ some individuals of pioneer species maintain their intitial foothold and don't disappear from the community

◦ new species immigrate from other locations

• falls slightly (but still relatively high) in climax communities

◦ specialized niches established

◦ weaker organisms out-competed for resources (competitive exclusion) Mineral cycling

-• low during early stages of succession

◦ not many producers to break down bare rock ◦ limited time for erosion to build soil matrix

◦ limited soil = few soil microbes to cycle minerals and nutrients

• increases rapidly throughout succession

• remains relatively high during climax community

◦ especially high in tropical zones due to year-round growth

2.6.7 Describe factors affecting the nature of climax

communities.

2.7.1 Describe and evaluate methods for measuring changes in

abiotic and biotic components of an ecosystem along an

environmental gradient.

Environmental gradient - a gradual change in one or more abiotic factors through distance, depth, and/or time

←distance from a body of water

←depth from surface of soil or water

←distance from a valley or mountain ridge

Abiotic components - the physical characteristics of the ecosystem, which change depending on the type of ecosystem being studied; some of these factors are closely related and interdependent upon one another

←humidity

←temperature

←light intensity

←dissolved oxygen

←wave action

Biotic components - the living parts of an ecosystem and their interactions, which are largely dependent upon the abiotic components listed above; given enough time, biotic factors may also impact the abiotic factors in an ecosystem

←species composition

←diversity

←interactions (mutualism, commensalism, intra- and interspecific competition)

←productivity levels

2.7.2 Describe and evaluate methods for measuring changes in

abiotic and biotic components of an ecosystem due to a specific

human activity

2.7.3 Describe and evaluate the use of environmental impact

assessments (EIAs).

Environmental Impact Assessments (EIA's) are "An examination of the likely impacts of development proposals on the environment prior to the beginning of any activity."

(www.business2000.ie/resources/Glossary_E.html)

EIA’s are prepared before construction or development on a project begins. EIA’s are meant

to inform and guide the decisions made regarding a project. They are designed to quantify (measure) what the environment is like now and project how it would be affected by the project. These projects are usually quite large and include considerable government involvement. Typical projects requiring EIA’s:

←dams

←roads

←ports

←airports

←power plants

←subdivisions (large-scale suburban housing developments)

EIA's include several different components:

←Baseline study - Determines the current state of the site’s environment

◦measure the abiotic factors before the site is disturbed (some examples are listed below, but these are not a complete list)

←microclimate

←water, soil, &/or air quality

←stream flow

◦measure the biotic factors and diversity within an area ←species richness

←species evenness

←endangered species

◦impacts on human populations

←health

←economics

←social and/or cultural impacts

←Scoping - Identifies and assesses the possible impacts ◦What will definitely change?

◦How will it change?

◦How much will it change? (scaling) ◦How will that change affect:

←diversity of flora and fauna ←people living in or near the area

←physical (abiotic) components of the nearby ecosystem

◦What constitutes “acceptable” levels? Who determines those levels? ◦What must be done to limit those impacts?

◦Who is responsible for those actions?

◦Who is responsible for monitoring the changes?

◦What are the consequences for exceeding the acceptable levels of change?