ESS Chap 2

Species

group of organisms that share similar characteristics that interbreed and produce offspring

Habitat

environment in which a species normally lives

Niche

where, when and how an organism lives
- Fundamental Niche: the theoretical niche. The full potential of where, when and how a species can exist.
- Realised Niche: where the species actually exist

Abiotic Factors

nonliving parts of the environment and determine the fundamental and realised niche of species
- There are tolerance ranges (limits) and optimal ranges for which a species can thrive in

Carrying capacity

number of organisms/size of population that an area can support sustainably over a long period of time

Biotic factors: predation

- occurs when one animal/plant hunts and eats another organism
- These predator prey interactions are often controlled by negative feedback mechanisms that control population densities
- In the relative absence of the predator the population of prey begins to increase and as the availability of prey increases, predators also increase.... And the cycle continues
- Predation may be good for the prey, it removes old and sick individuals first as they're easier to catch and those remaining are healthier and form a superior breeding pool

Biotic factors: herbivory

- interaction where an animal feeds on a plant
- Carrying capacity of a herbivore's environment is affected by the quantity of the plant it feeds on as an area with more abundant plants has a higher carrying capacity

Biotic factors: parasitism

- form of symbiosis where one of the organisms is harmed
- parasites benefit at the expense of another organism from which it drives food
- Carrying capacity of host may be reduced because of the harm caused by the paradise

Biotic factors: mutualism

- form of symbiosis where both species benefit
- relationship in which two organisms live together

Biotic factors: disease

- form of symbiosis where both species are harmed
- Disease causing species may reduce the carrying capacity of the organism it is infecting

Biotic factors: competition

- when resources are limiting, populations compete to survive
- Either within a species (intraspecific competition) or between different species (interspecific competition)
- No two species can occupy the same niche so the degree to which niches overlap determines the degree of interspecific competition

S population curve

- when a graph of population growth for species is plotted against time (x axis).
- An S-shaped curve shoes an initial rapid growth then slows down as the carrying capacity is reached

S population curve steps

1) Lag Phase
- population numbers are low leading to low birth rates
- Few individuals colonise an area and because number of them are low, birth rates are low
2) Exponential growth phase
- population grows at a rapid rate
- Limiting factors not restricting growth
- Favourable abiotic components
- Numbers of individuals increase, so does the birth rate
3) Transitional phase
- population growth slows down, but still continues to grow
- Limiting factors begin restricting its growth
- Increased competition for resources
- Increase in predators and disease due to increased numbers of individuals living in a small area
4) Stationary phase
- population growth stabilises and population fluctuates around a level that represents its carrying capacity
- Limiting factors restrict population to its carrying capacity
- Changes in limiting factors and abiotic ones cause populations to fluctuate around capacity

J population curve

acceleration of growth

J population curve process

- Initially slow but becomes increasingly rapid and doesn't slow down as population increases
- Organisms with this tend to produce many offspring rapidly and have little parental care
- The growth occurs when limiting factors aren't restricting the growth, there are plentiful resources and favourable abiotic components
- Sudden decrease in population is called population crash
- Populations With J curve generally controlled by abiotic but not biotic components (but food can also cause crashes)

Limiting factors for plants

light, nutrients, water, CO2 and temperature

limiting factors for animals

space, food, mates, nesting sites and water

Limiting factors for carrying capacity

availability of food and water, territorial space, predation, disease, availability of mates.

Community

many species living together in a common habitat

ecosystem

community and the physical environment it interacts with

Photosynthesis

- produces raw material for producing biomass
- Inputs: sunlight as energy source, carbon dioxide and water
- Outputs: glucose (used as an energy source) and oxygen
- Transformation: energy change from light energy into stored chemical energy (chlorophyll is needed to allow the sunlight energy to be transformed into chemical)

Respiration

- Inputs: glucose and oxygen
- Outputs: release of energy for work and heat
- Transformations: from stored chemical energy (from photosynthesis) into kinetic energy and heat. Most is eventually lost as heat
- During respiration large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling the organisms to maintain relatively low entropy

Feeding Relationships: producers

- Supports ecosystem with constant input of energy and new biological matter (biomass)
- Also known as autotrophs (organism that makes its own food)

Feeding relationships: consumers

- Organisms that can't make their own food so they eat other organisms
- Heterotrophs
- Herbivores feed on autotrophs, Carnivores feed on other heterotrophs, Omnivores feed on both-

Heterotroph

An organism that cannot make its own food.
- an organism that eats other plants or animals for energy and nutrients

Feeding relationships: decomposers

- Obtain their food and nutrients from the breakdown of dead organic matter
- Form the basis of a decomposer food chain

pyramid of numbers

* Numbers of producers and consumers coexisting in an ecosystem
* In accordance with the 2nd law of thermodynamics, there's a tendency for numbers to decrease along food chains but pyramids of numbers aren't always pyramid shaped
* a: simple and easy method of giving an overview and is good at comparing changes in population numbers with time or season
* d: all organisms included regardless of size, therefore a pyramid based on an oak tree would be inverted and numbers can be too great to represent accurately

Pyramid of biomass

* May be measured in grams per metre squared units of energy like joules per metre squared
* In accordance with the 2nd law of thermodynamics, biomass tend to decrease along food chains
* Eg: phytoplankton vary in productivity therefore in biomass depending on sunlight intensity so the biomass of them can change
* a: overcomes some problems with pyramids of numbers

Pyramids of productivity

* Flow of energy through a trophic level indicating the rate at which that storage is being generated
* Take into account the rate of production over a period of time because each level represents energy per unit area per unit time
* Productivity measured in mass/energy per metre squared per year
* They show the flow of energy through an entire ecosystem over a year, thus are more useful of measuring changes than biomass
* No inverted pyramids
* Overcomes the problem that two species may not have the same energy content per unit weight (these cases make biomass misleading but energy flow is directly comparable)
* In accordance to the second law of thermodynamics, energy always decreases up as energy is lost and entropy increases
* In accordance to the first law of thermodynamics, energy lost by changing into different energies through movement, excretion, egestion...etc
* disadvantage: it’s difficult to collect energy data as the rate of biomass production over time is required

example of realized and fundamental niches

• A specie of barnacles, Semibalanus, was most abundant on the middle and lower intertidal area and that the other specie, Chthamalus, was most common on the upper intertidal area of the shore.

• When the Chthamalus was removed from the upper area of shore, it was found that no Semibalanus replaced it

• explanation was that Semibalanus could not survive in an area that regularly dried out due to low tides.

• He concluded that Semibalanus' realized niche was the same as its fundamental niche.

• In another experiment he removed Semibalanus from the lower and middle areas. He found that over time Chthamalus replaced it in the middle intertidal zone: his explanation was that Semibalanus was a more successful competitor in the middle intertidal zone and usually excluded Chthamalus. He concluded that the fundamental niche and realized niche for Chthamalus were not the same and that its realized niche was smaller due to interspecific competition (i.e. competition between species) leading to competitive exclusion (when one species outcompetes and excludes another when their niches overlap, page 69).

tolerance limits - abiotic factors

- All plants and animals need water to survive. For plants, water stress (too little water) may cause germination to fail, seedlings to die, and seed yield to be reduced. Plants are extremely
sensitive to water level.

intraspecific competition

competition between members of the same species
- For example, a large oak tree will fare better than the small sapling growing in its shade. If it grows near other, more established trees, the sapling will struggle to obtain nutrients from the soil and sunlight from the sky.

interspecific competition

competition between members of different species
- eg: between lions and leopards that vie for similar prey and interspecific competition between rice paddies with weeds growing in the field.

example of food web

1) bacteria
2) carrots/grass (@ bacteria (from snake))
3) rabbit / grasshoper
4) foxes/ owls (@grasshoppers)/ birds (@grasshoppers)/snake (@grasshopper)

bioaccumalation

the build-up of persistent/non-biodegradable pollutants within
an organism or trophic level because they cannot be broken down.

biomagnification

is the increase in concentration of persistent/non biodegradable pollutants along a food chain.

Bioaccumulation and biomagnification example: DDT

Toxins such as DDT and mercury accumulate along food chains due to the decrease of biomass and energy.
- bioacumultion: non-biodegradable pesticide DDT on food
chains. The producers, algae and plants or grass (first accumulators) take in the DDT. Organisms in the second trophic level (the primary consumers) eat the DDT-containing producers and retain the pesticide in their body tissue (mainly in fat)
- biomagnification: The pesticide accumulates in body fat and is not broken down. Each successive trophic level supports fewer organisms, so the pesticide becomes increasingly concentrated in the tissues

Transfer and Transformation of Energy:

* The pathway of sunlight entering the Earth’s atmosphere is complex because sunlight contains a broad spectrum of of wavelengths 
* As solar radiation enters the Earth’s atmosphere, some energy becomes unavailable for ecosystems as the energy is being absorbed by inorganic matter and reflected back into the atmosphere. Most energy doesn’t end up as biomass in ecosystems.
* Around 51% of available energy doesn’t reach producers. First, much of the incoming solar radiation fails to enter the chloroplast because it is reflected, transmitted or is the wrong wavelength to be absorbed. Of the radiation absorbed, only a small amount ends up as biomass as the conversion of light to chemical energy is inefficient. 

Ecological Efficiency:

* Percentage of energy transferred from one trophic level to another is called **ecological efficiency.** Ecological efficiency averages on 10% but vary from 5-20


* Ultimately all energy lost from an ecosystem is in the form of heat through the insufficient energy transfer in respiration. From light to heat, and then heat is re-radiated into the atmosphere
* Systems diagrams showing energy flow in an ecosystem are represented through arrows. Arrows also represent productivity.

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Primary productivity

* The gain by producers in energy or biomass per unit area per unit time
* The conversion of solar energy into chemical energy. It depends on the amount of sunlight and the ability of producers to use energy to synthesise organic compounds and other factors
* It’s highest where conditions for growth are optimal. For eg: tropical rainforests have high rainfall and are warm throughout the year so they have a high productivity and constant growing season. Deep oceans are dark below surface and this limits plant productivity

Secondary Productivity

* The biomass gained by heterotrophic organisms through feeding and absorption, measured in units of mass/energy per unit area per unit  time
* It involves feeding and absorption and depends on the amount of food present and the efficiency of consumers turning this into new biomass

Gross Productivity

The total gain in energy/biomass per unit area per unit time

Net Productivity

the gain in energy/biomass per unit area per unit time subtracting respiratory losses 

**Gross Primary Productivity (GPP)**

equivalent to the mass of glucose created by photosynthesis per unit area per unit time in primary producers 

**Net Primary Productivity (NPP)**

the gain by producers in energy/biomass per unit area per unit time remaining after subtracting respiratory losses. NPP is the potential energy available to consumers in an ecosystem. 

* NPP = GPP - R (respiratory losses)

**Gross Secondary Productivity (GSP):**

 total energy/biomass assimilated/absorbed by consumers

* GSP = food eaten - faecal loss

**Net Secondary Productivity (NSP)**

gain by consumers in energy/biomass per unit area per unit time after subtracting respiratory losses

* NSP = GSP - R

Experiment for NPP and GPP:

* Using aquatic plants, GPP and NPP can be measured through photosynthesis and respiration. Both processes produce/use oxygen so measuring dissolved oxygen will give an indirect measurement of the rate of photosynthesis and respiration.
* An aquatic plant was put in light and dark conditions. Dissolved oxygen is measured before and after the plant was put into the light and dark. 

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NPP: 

* Measure the increase in dissolved oxygen when aquatic plants are put into the light. In light both photosynthesis and respiration are occurring but photosynthesis is the bigger process as it produces more oxygen then the plant uses in respiration
* NPP = GPP - R
* Measured in dissolved oxygen in milligrams of oxygen per litre per hour

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Respiration:

* Can be calculated by measuring the decrease in dissolved oxygen when aquatic plants are put into the dark as in the dark, only respiration occurs and not photosynthesis. 
* GPP = NPP + R
* Measured in dissolved oxygen in milligrams of oxygen per litre per hour

Experiment for NSP and GSP:

* A total of 10 stick insect were fed privet leaves for 5 days

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NSP:

* Calculated by measuring the increase in biomass in stick insects over a specific amount of time. This increase is equal to the mass of food eaten by the stick insects minus biomass lost through respiration and faeces
* NSP = mass of stick insects at end of experiment - mass of stick insects at start of experiment

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GSP:

* GSP = food eaten - faecal loss
* Food eaten is the mass of leaves at the start of the experiment - mass of leaves at the end of the experiment
* Facel loss is the mass of faeces at the end of the experiment 
* GSP is therefore the amount of food absorbed by the consumer

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Respiration:

* R = GSP - NSP

Sustainable Yield:

* Rate of an increase in natural capital (ie: natural income) that can be exploited without depleting the original stock or its potential for replenishment
* The annual sustainable yield for a crop is equivalent to the annual gain in biomass or energy through growth/recruitment
* Maximum sustainable yield is the maximum flow of a given resource so the stock doesn’t decline overtime. It’s equivalent to the net primary productivity or net secondary productivity of a system. 
* Net productivity is measured in the amount of energy stored as new biomass per year, and so any removal of biomass at a rate greater than this rate means the NPP or NSP would not be able to replace the biomass extracted. Harvesting above these rates will be unsustainable and will lead to a reduction in natural capital.

Nutrient Cycles:

* Nutrients are circulated and reused frequently but only oxygen, carbon, hydrogen and nitrogen are needed in large quantities (macronutrients) the rest are needed in small quantities (micronutrients)
* Nutrients are taken in by plants and built into new organic matter and when animals eat the plants, they take up said nutrients and eventually return them to the soil when they die. They are also broken down by decomposers and when animals defecate and excrete. 
* Matter flows through ecosystems linking them together. This flow of matter involves transfers and transformations.
* The carbon and nitrogen cycles are used to illustrate this flow of matter using flow diagrams. These cycles contain storages (sometimes referred to as sinks) and flows, which move matter between storages

Carbon Cycle: storages

* Organisms 
* Atmosphere
* Soil 
* Fossil fuels
* Ocean

Carbon cycle: transfers

* Herbivores feeding on producers
* Carnivores feeding on herbivores
* Decomposers feeding on dead organic matter
* Carbon dioxide from the atmosphere dissolving in rainwater oceans

Carbon cycle: transformations

* Photosynthesis transforms CO2 and water into glucose using sunlight energy trapped by chlorophyll
* Respiration converts organic matter such as glucose into CO2 and water
* Combustion transforms biomass into CO2 and water
* Fossilization transforms organic matter in dead organisms into fossil fuels through incomplete decay and pressure

Nitrogen Cycle: stroages

* Organisms
* Soil
* Fossil fuels
* Atmosphere
* Water bodies

Nitrogen Cycle: transfers

* Herbivores feeding on producers
* Carnivores feeding on herbivores
* Decomposers feeding on dead organic matter
* Plants absorbing nitrates through their roots
* Removal of metabolic waste products from an organism (excretion)

Nitrogen Cycle: transformations

* Lightening transforms nitrogen in the atmosphere into NO3; nitrogen fixation. It also can fix atmospheric nitrogen into ammonia.
* Nitrogen-fixing bacteria transform nitrogen gas in the atmosphere into ammonium ions. They’re found free-living in soil or within root nodules.
* Nitrifying bacteria transform ammonium ions into nitrite and then nitrate. They’re found in the soil and gain energy from this reaction to form food (glucose). Ammonia and nitrates are toxic to plants but the nitrates are taken up with water to produce amino acids and other organic chemicals.
* Denitrifying bacteria transform nitrates into nitrogen and return nitrogen back to the atmosphere. They remove oxygen from nitrates (as they live on oxygen-poor soil so free oxygen is not readily available) and nitrogen gas is released as a by-product. This is why waterlogged soil isn’t good for farmers as nitrates are reduced by denitrifying bacteria.
* Decomposers break down organic nitrogen into ammonia, the breakdown of organic nitrogen into ammonia is deamination
* Nitrogen from nitrates is used by plants to make amino acids and protein; assimilation

Impact of Human Activities: Energy Flows:

* Human activities like burning fossil fuels, deforestation, urbanisation and agriculture impact energy flows
* Combustion of fossil fuels increases carbon dioxide levels, and therefore in temperature. This has led to the reduction in Arctic land and sea ice, reducing the amount of reflected sunlight energy. 

Impact of Human Activities: Matter Cycles:

* Timer Harvesting interferes with nutrient cycling. For eg: tropical rainforests have soil with low fertility and nutrient cycles between the leaf litter and tree biomass. Once trees are removed, there is no canopy that intercepts rainfall and the soil and leaf litter is washed away and with it much of the available nutrients
* Once the original forest has been removed, natural nutrient recycling is lost. 
* In South East Asia large areas have been cleared to grow palm oil as it is used for fuel and food production. The soil is nutrient poor so oil palm trees require fertilisers to produce yields that earn a reasonable profit. But adding fertilisers, especially ones containing nitrates, can cause eutrophication in nearby bodies of water when nitrates runoff from soils, causing disruption to the ecosystem.
* When crops are harvested and taken away, they contain nitrogen and that nitrogen is also transported. The changes to nitrogen storage locations can alter the cycle and cause disruption to ecosystems.
* Increased carbon dioxide levels from fossil fuel burning can lead to increased vegetation growth because there is more carbon dioxide available for photosynthesis, altering the carbon cycle. 
* Mining and burning fossil fuels also reduces the storage of these non-renewable sources of energy and increases the storage of carbon in the atmosphere. 

Biomes:

* Abiotic factors and species distinguish each biome from another. Precipitation (water), insolation and temperature are the climates that control how biomes function, structure and location.
* Water is needed for photosynthesis, transpiration and cell support. Sunlight is needed for photosynthesis. Rate of photosynthesis is affected by temperature and determines the NPP of an ecosystem 

They are grouped into 5 major classes:

* Forest
* Desert
* Tundra
* Grassland
* Aquatic

Effect of Climate Change on Biome Distribution:

* Distribution of biomes are controlled by temperature, insolation and precipitation. Increases in CO2 and other greenhouse gases lead to an increase in global mean temperature which in turn affects rainfall patterns. These changes in climate affect biome distribution.
* increase in mean global temperature and other changes and lead to adaptations needing to be made.
* biomes are also shifting like in the Aritc, tundras are becoming shrublands
* animals can migrate but there are obstacles like human made ones (roads) and natural ones (mountain ranges)
* hotspots are predicted to have high turnover of species due to climate change like Madagascar
* biomes changing also mean new oppurtunities to exploit resources, eg: drilling for oil under the Artic Ocean is becoming possible with the decrease of sea ice

Tropical Rainforest distribution

**Distribution:**

* within 5 degrees North and South of the equator

Tropical Rainforest structure

* Rainforests show a highly layered, or stratified, structure. There are tall emergent trees, a canpoy of others, understorey of smaller trees and shrub layer under this
* Because soils in rainforest are thin, trees have shallow root systems with one long tap root running from the centre of the trunk into the ground plus wide buttresses to help support the tree.
* little light reaches the forest floor and few plants live there; nearly no plants grow there and all sunlight has been intercepted before it cna reach the ground

Tropical Rainforest biodiveristy

* amazingly high levels of biodiversity, many species and many individuals of each species
* The high diversity of plants is because of the high levels of productivity resulting from year-round high rainfall and insolation.
* High productivity in the canopy results in high biodiversity, and it is believed that half of the world’s species could be found in rainforest canopies.

Tropical Rainforest: Relative Productivity

* Their position in low latitudes, with the Sun directly overhead, determines their climatic conditions, and enables high levels of photosynthesis and high rates of NPP throughout the year.
* Tropical rainforests are estimated to produce 40 percent of NPP of terrestrial ecosystems.
* Only about 1 percent of light hitting the canopy layer reaches the floor, so the highest levels of NPP are found in the canopy – one of the most productive areas of vegetation in the world.
* Although rainforests are highly productive, much of the inorganic nutrients needed for growth are locked up in the trees. The soil is low in nutrients.
* Trees obtain their nutrients from rapid recycling of detritus that occurs on the forest floor. If rates of decay are high enough, the forest can maintain levels of growth.
* but respiration is also high and for a larger mature tree in the rainforest, all glucose made in photosynthesis is used in respiration so there is no net gain. but when rainforest plants are imature their growth rates are huge and biomass gain very high

Tropical Rainforest: Temperature

* high, typically 26C
* There is little seasonal variation in temperature.

Tropical Rainforest Precipitation

* high rainfall throughout the year
* rain washes nutrients out of the soil (leaching) so nutrients may be limiting plant growth
* However, heavy rainfall can cause nutrients to be washed from soils (leaching) resulting in an increased lack of inorganic nutrients that could limit primary production.
* The forest canopy provided by the trees protects the soils from heavy rainfall but once areas have been cleared through logging, the soils are quickly washed away (eroded) making it difficult for forests to re-establish (it may take about 4000 years for a logged area to recover its original biodiversity.

Tropical Rainforest Insolation

* experience high light levels throughout the year 
* There is little seasonal variation in sunlight but monsoon periods can reduce levels of insolation, providing an all year growth season.

Tropical Rainforest: human activity

* with fewer humans, the forest could provide enough resources for the population but there are now too any exploiting the forest and it doesn’t have enough time to recover due to the density of human population in the tropics and subtropics
* commerical logging of valuable timber and converting land to grazing cattle destroys the forest

Temperate Forest: distribution

* Temperate forests are largely found between 40° and 60° N of the equator
* They are found in seasonal areas where winters are cold and summers are warm, unlike tropical rainforests which enjoy similar conditions all year round.
* eg: US Pacific Northwest

Temperate Forest: structure

* **Two different tree types are found in temperate forest – evergreen (which leaf all year round) and deciduous (which lose their leaves in winter). Evergreen trees have protection against the cold winters (thicker leaves or needles), whereas deciduous trees have leaves that would super frost damage, so they shut down in winter.**
* There is some layering of the forest, although the tallest trees generally do not grow more than 30 m, so vertical stratification is limited. The less complex structure of temperate forests compared to rainforest reduces the number of available niches and therefore species diversity is much less.
* fewer species than tropical rainforests
* leaf litter and rapid recycling of nutrients but some are lost through leaching

Temperate Forest: biodiversity

* **Forests might contain only deciduous trees, only evergreens, or a mixture of both.**
* Diversity is lower than in rainforest and the structure of temperate forest is simpler. These forests are generally dominated by one species and 90 per cent of the forest may consist of only six tree species. 

Temperate Forest: relative productivity of contrasting biomes

* **But temperate forests have the second highest NPP (after rainforests) of all biomes.**
* leaf fall in winter so reduced photosynthesis and transpiration and frozen soils when water is limiting, temperatures and insolation lower in winter

Temperate Forest: temperature

* **The mild climate, with lower average temperatures and lower rainfall than are found at the equator, also reduces levels of photosynthesis and productivity compared to tropical rainforest.**
* The forest floor has a reasonably thick leaf layer that is rapidly broken down when temperatures are higher, and nutrient availability is in general not limiting. 

Temperate Forest: precipitation

* **At these mid-latitudes the amount of rainfall determines whether or not an area develops forest – if precipitation is sufficient, temperate forests form; if there is not enough rainfall, grasslands develop. Rainfall in these biomes is between 500 and 1500 mm yr–1.** 

Temperate Forest: insolation

* **Variation in insolation during the year, caused by the tilt of the Earth and its rotation around the Sun, means that productivity is lower than in tropical rainforests as there is a limited growing season.** 
* The lower and less dense canopy means that light levels on the forest floor are higher than in rainforest, so the shrub layer can contain many plants such as brambles, grasses, bracken, and ferns.

Temperate Forest: human activity

* much temperate forest has been cleared for agriculture or urban developments
* large predators virtually wiped out
* most of Europe’s natural primary natural primary deciduous woodland has been cleared for farming for use as fuel and in building

Deserts: distribution

* **Deserts are found in bands at latitudes of approximately 30° N and S**
* **They cover 20–30 per cent of the land surface. It is at these latitudes that dry air descends having lost water vapour over the tropics; mostly in the middle of continents**
* The Sahara Desert in northern Africa is the world’s largest desert. Covering more than 9 million square kilometres (3.5 million square miles), it is slightly smaller than the USA.

Deserts: structure

* **Soils can be rich in nutrients as they are not leached away; this helps to support the plant species that can survive there.**
* plants are drought resistant and mostly cacti and succulents with adaptations

Deserts: biodiversity

* **The species that can exist in deserts are highly adapted, showing adaptations to reduce water loss in dry conditions**
* **Cacti (a group restricted to the Americas) have reduced their surface area for transpiration by converting leaves into spines. They store water in their stems, which have the ability to expand, enabling more water to be stored and decreasing the surface area : volume ratio thus further reducing water loss from the surface**
* animals are adapted to drought conditions; reptiles are dominant. small mammals can survive by adapting to be nocturnal or reduce water loss by having no sweat glands and absorbing water from their foods
* Snakes and reptiles are the commonest vertebrates – they are highly adapted to conserve water and their cold blooded metabolism is ideally suited to desert conditions. Mammals have adapted to live underground and emerge at the coolest parts of day.

Deserts: relative productivity

* **Decomposition levels are low because of the dryness of the air and lack of water.**
* The lack of water limits rates of photosynthesis and so rates of NPP are very low.
* both primary and secondary are low in net productivity because water is limiting and plant biomass cannot build up to large amounts
* food chains tend to be short because of this

Deserts: temperature

* Hot deserts are characterised by high temperatures at the warmest time of day (typically 45–49°C) in early afternoon
* Organisms also have to overcome fluctuations in temperature (night temperatures, when skies are clear, can be as low as 10 °C, sometimes as low as 0 °C), which makes survival difficult. Low productivity means that vegetation is sparse

Deserts: precipitation

* **low precipitation (typically under 250 mm yr–1) at the warmest time of day** 
* Rainfall may be unevenly distributed. 
* Roots can be both deep (to access underground sources of water) and extensive near the surface (to quickly absorb precipitation before it evaporates). 
* The spiny leaves deter animals from eating the plants and accessing the water. Xerophytes have a thick cuticle that also reduces water loss. 
* However, the Sahara Desert  is not the site of the world’s lowest rainfall – that occurs in Antarctica, which receives less than 50 mm of precipitation annually.

Deserts: human activity

* population density has been low as the environment cannot support large numbers
* irrigation is possible by tapping underground water stores or aquifers in some deserts, crops are grown. but there is a high rate of evaporation of this water and as it evaporates it leaves salts behind, eventually these reach such high concentrations that crops will not grow and salinization occurs
* desertification can occur when an area becomes a desert either through overgrazing or drought

Tundra: distribution

* Most of the world’s tundra is found in the north polar region, and so is known as Arctic tundra. There is a small amount of tundra in parts of Antarctica that are not covered with ice, and in lower latitudes on high altitude mountains (alpine tundra).

Tundra: structure

* **Soil may be permanently frozen (permafrost) and nutrients are limiting. Low temperature means that the recycling of nutrients is low, leading to the formation of peat bogs where much carbon is stored. low inorganic matter and minerals**
* no trees but thick mat of low growing plants; adapted to withstand drying out

Tundra: biodiversity

* **The vegetation consists of low scrubs and grasses.**
* Only small plants are found in this biome because there is not enough soil for trees to grow and, even in the summer, the permafrost drops to only a few centimetres below the Surface.
* animals are adapted with thick fur and small ears to reduce heat loss
* mostly small mammals
* most hibernate and make burrows
* LOW BIODIVERSITY

Tundra: relative productivity

* **In the summer, animal activity increases, due to increased temperatures and primary productivity. The growing period is limited to 6 weeks of the year, after which temperatures drop again and hours of sunlight decline.**
* very low productivity; slow decompositon so any peat bogs where most carbon is stored

Tundra: temperature

* **Temperatures are very low for most of the year; temperature is also a limiting factor because it affects the rate of photosynthesis, respiration, and decomposition (these enzyme-driven chemical reactions are slower in colder conditions).** 
* During winter months, temperatures can reach –50°C: all life activity is low in these harsh conditions. Plants are adapted with leathery leaves or underground storage organs, and animals with thick fur. Arctic animals are, on average, larger than their more southerly relations, which decreases their surface area relative to their size enabling them to reduce heat loss (e.g. the Arctic fox is larger than the European fox). 

Tundra: precipitation

* **Water may be locked up in ice for months at a time and this combined with little rainfall means that water is also a limiting factor.**

Tundra: insolation

* Tundra is found at high latitudes where insolation is low (Figure 2.39). Short day length also limits levels of sunlight.
* Low light intensity and rainfall mean that rates of photosynthesis and productivity are low. 
* In summer, the tundra changes: the Sun is out almost 24 hours a day, so levels of insolation and temperature both increase leading to plant growth. 

Tundra: human activity

* few humans but mining and oil
* the most fragile ecosystem that will take a very long time to recover from disruption. mining and oil extraction in canada and serbia destroy tundra
* global warming caused by greenhouse gases may eliminate Artic regions; global rise in temperature melt snow cover and parts of permafrost
* plants will die, animals migrating patterns change and the tundra biome will be gone
* very large amount of methane are locked up in tundra ice; if these are released into the atmosphere then huge increase in greenhouse gases

Grasslands: distribution

* 40-60 degrees North of equator
* **Grasslands are found on every continent except Antarctica, and cover about 16 percent of the Earth’s surface.**
* **There are several types of grassland: the Great Plains and the Russian Steppes are temperate grasslands; the savannahs of east Africa are tropical grassland.**

Grasslannds: structure

* They are found in the area where the polar and Ferrel cells meet and the mixing of cold polar air with warmer southerly winds (in the northern hemisphere) causes increased precipitation compared to polar and desert regions.
* Grasses grow beneath the surface and during cold periods (more northern grasslands during a harsh winter) can remain dormant until the ground warms.

Grasslannds: biodiversity

* **Grasses have a wide diversity** 

Grasslannds: relative productivity

* **low levels of productivity**
* Decomposing vegetation forms a mat containing high levels of nutrients, but the rate of decomposition is not high because of the cool climate. 

Grasslannds: temperature

* Grasslands away from the sea have wildly fluctuating temperatures which can limit the survival of animals and plants.
* temperature range high as not near the sea to moderate temperatures

Grasslannds: precipitation

* **They develop where there is not enough precipitation to support forests, but enough to prevent deserts forming.**
* Rainfall is approximately in balance with levels of evaporation.
* low rainfall, threat of drought

Grasslands: human activity

* black earth soils are deep and rich in organic matter so ideal for agriculture
* overgrazing reduces them to desert or semi-desert
* overcropping and drought led to soil being blown away on great Plains in 1930s

Tropical Coral Reefs: structure

* **Small animals called polyps take carbon dioxide and calcium from seawater and transform it into calcium carbonate skeletons (which form the reef).**