2.4 - Biomes, Zonation And Succession Flashcards
(122 cards)
1
Q
Define biomes
A
are collections of ecosystems sharing similar climatic conditions which can be grouped into five major classes - aquatic, forest, grassland, desert and tundra. Each of these classes will have characteristic limiting factors, productivity and biodiversity.
2
Q
What are the main factors governing the distribution of biomes
A
Insolation, precipitation and temperature are the main factors governing the distribution of biomes.
3
Q
What is the tricellular model
A
The tricellular model of atmospheric circulation explains the distribution of precipitation and temperature influencing structure and relative productivity of different terrestrial biomes.
4
Q
What is causing biome shifts
A
Climate change is altering the distribution of biomes and causing biome shifts.
5
Q
Define zonation
A
Zonation refers to changes in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore (coverage by water).
6
Q
Define succession
A
Succession is the process of change over time in an ecosystem involving pioneer, intermediate and climax communities.
7
Q
What changes during succession
A
During succession the patterns of energy flow, gross and net productivity, diversity and mineral cycling change over time.
8
Q
What leads to greater habitat diversity
A
Greater habitat diversity leads to greater species and genetic diversity.
9
Q
What do r and k strategist species have
A
r and K strategist species have reproductive strategies that are better adapted to pioneer and climax communities respectively.
10
Q
What is the energy like in the early stages of succession
A
early stages of succession, gross productivity is low due to the unfavourable initial conditions and low density of producers. The proportion of energy lost through community respiration is relatively low too, so net productivity is high, that is, the system is growing and biomass is accumulating.
11
Q
What is the energy like in the later stages of succession
A
In later stages of succession, with an increased consumer community, gross productivity may be high in a climax community. However, this is balanced by respiration, so net productivity approaches zero and the productivity:respiration (P:R] ratio approaches one.
12
Q
What contributes to the stability of an ecosystem
A
In a complex ecosystem, the variety of nutrient and energy pathways contributes to its stability.
13
Q
Is there one climax community
A
There is no one climax community but rather a set of alternative stable states for a given ecosystem. These depend on the climatic factors, the properties of the local soil and a range of random events which can occur over time.
14
Q
What one factor can divert the progression of succession
A
Human activity is one factor which can divert the progression of succession to an alternative stable state, by modifying the ecosystem, for example the use of fire in an ecosystem, use of agriculture, grazing pressure, or resource use such as deforestation. This diversion may be more or less permanent depending upon the resilience of the ecosystem.
15
Q
Define biosphere
A
The biosphere is that part of the Earth inhabited by organisms. It extends from the upper part of the atmosphere down to the deepest parts of the oceans which support life.
16
Q
State the 5 biomes
A
Aquatic - freshwater and marine
- Freshwater - swamp forests, lakes and ponds, streams and rivers, bogs
- Marine - rocky shore, mud flats, coral reel, mangrove swamp, continental shelf, deep ocean
Deserts - hot and cold
Forests - tropical, temperate and boreal (taiga)
Grassland - tropical or savanna and temperate
Tundra - Arctic and alpine.
17
Q
What alters the types of biome
A
Each of these biomes will have characteristic limiting factors, productivity and biodiversity. Isolation, precipitation and temperature are the main factors governing the distribution of biomes.
18
Q
What alters where biomes are located
A
The climate is the major factor that determines what grows where and so what lives where. The other important factor is the terrain or geography - slope, aspect and altitude. Climate is made up of general weather patterns, seasons, extremes of weather and other factors but two factors are most important - temperature and precipitation (rain and snowfall).
19
Q
What affects the temperature from the poles to the equator
A
The temperature is hotter nearer the equator and generally gets cooler as we go towards the poles (increase latitude). This is due to the fact the suns rays hit the Earth at a more acute angle and so are spread over a greater surface area. You can see this effect if you shine a torch beam directly at an object which is flat in front of the torch or shining it at an angle.
20
Q
How does latitude and altitude alter the climate
A
Latitude (distance north or south from the equator) and altitude (height above sea level) both influence climate and biomes. It generally gets colder as you increase latitude or increase altitude. So there is snow on Mt Kilimanjaro and the Himalayas and Andes and they have alpine or polar biomes even though they are at lower latitudes
21
Q
How does oceans and winds distribute surplus heat
A
Ocean currents and winds distribute surplus heat energy at the equator towards the poles. Air moving horizontally at the surface of the Earth is called wind. Winds blow from high to low pressure areas. Winds cause the ocean currents. It is water that is responsible for transferring the heat. Water can exist in three states - solid (ice and snow), liquid (water) and gas (water vapour). As it changes from state to state it either gives out or takes in heat. This is its latent heat.
22
Q
What happens to energy when water changes from solid to liquid
A
As water changes from solid to liquid (melts) to gas (evaporates), it takes in heat as more energy is needed to break the molecular bonds holding the molecules together.
23
Q
What happens to energy as water changes from gas to liquid
A
As water changes from gas to liquid (condenses) to solid (freezes), it gives out heat to its surroundings. It is this change that distributes heat around the Earth. Water is the only substance that occurs naturally in the atmosphere that can exist in the three states within the normal climatic conditions on Earth.
24
Q
What angle is the earth tilted
A
As well as orbiting around the Sun, the Earth rotates and is tilted at 23.5 degrees on its axis. It takes 365 days (and a quarter) for the Earth to go once round the Sun and this gives us a year and our seasons.
25
What are the most important abiotic factors that influence where biomes grow and are located and what must we use to compare them
Isolation, precipitation and temperature are the most important abiotic (physical) factors influencing biomes or what grows where. Increasing temperature causes increased evaporation so the relationship between precipitation and evaporation is also important. Plants may be short of water even if it rains or snows a lot if the water evaporates straight away (deserts) or is frozen as ice (tundra). So we must consider the precipitation to evaporation ratio
26
What happens when the precipitation is the same as evaporation
P/E ratio is approximately 1 when precipitation is about the same as evaporation; the soils tend to be rich and fertile.
27
What are some limiting factors affecting productivity in biomes
Different biomes have differing amounts of productivity due to limiting factors: raw materials or the energy source (light) for photosynthesis may be in short supply. Solar radiation and heat may be limited at the South Pole in winter, water in limited supply in a desert. All food webs depend on photosynthesis by green plants to provide the initial energy store so, if they cannot photosynthesize to their maximum capacity, other organisms will have a problem getting enough food.
28
Where is productivity greatest
Productivity is greater in low latitudes (nearer the equator), where temperatures are high all through the year, sunlight input is high and precipitation is also high.
29
Where is productivity lowest
Moving towards the poles, where temperatures and amount of sunlight decline, the rate at which plants can photosynthesize is lower, and thus both GPP (gross primary productivity) and NPP values are lower. In the terrestrial areas of the Arctic, Antarctic and adjacent regions (ie in high latitudes), low temperatures, permanently frozen ground (permafrost), long periods in winter when there is perpetual darkness, and low precipitation (cold air cannot hold as much moisture as warm air) all tend to cause a reduction in photosynthesis and lower productivity values.
30
In which ways are the climate changing
• Temperature increase of 1.5 to 4.5 °C by 2100 (according to the IPCC)
• Greater warming at higher latitudes
• More warming in winter than summer
• Some areas becoming drier, others wetter
• Stronger storms.
31
In which ways is climate change affecting biomes
• towards the poles where it is cooler
• higher up mountains where it is cooler - 500 m of altitude decreases temperature about 3 °C
• towards the equator where it is wetter.
32
What are 2 examples of biomes shifting
• in Africa in the Sahel region, woodlands are becoming savannas
• in the Arctic, tundra is becoming shrubland.
33
What factors are affecting the migration of animals to new locations due to climate change
Plants can only migrate very slowly as seeds are dispersed by wind or animals. But animals can migrate longer distances, eg albatrosses, wildebeest, whales.But there are obstacles to migration - natural ones like mountain ranges and seas and ones caused by human activities such as roads, agricultural fields and cities. Animals may not be able to cross these and could become extinct.
34
What are the hotspots which are thought to have a high turnover due to the turnover of species due to climate change
• The Himalayas - sometimes called the third pole - as species can move no higher than the land mass.
• Equatorial Eastern Africa - with a very drought-sensitive climate.
• The Mediterranean region.
• Madagascar.
• The North American Great Plains and Great Lakes.
35
What are 2 benefits to humans as biomes change and become vulnerable
• Drilling for oil under the Arctic Ocean is becoming possible with the decrease in sea ice.
• The North- West Passage for ships between the North Pole and North
America could become a trade route without icing up.
36
LOOK AT THE TRICELLULAR MODEL PAGE 105 IN YELLOW BOX
37
What is a tropical rainforest
Hot and wet areas with broadleaved evergreen forest.
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Where are tropical rainforests
Within 5 degrees North and South of the equator.
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What are climate and limiting factors in tropical rainforests
High rainfall 2000-5000 mm yr 1. High temperatures 26-28 °C and little seasonal variation.
High insolation as near equator. P and E are not limiting but rain washes nutrients out of the soil (leaching) so nutrients may be limiting plant growth.
40
What is the structure of a tropical rainforest
Amazingly high levels of biodiversity - many species and many individuals of each species. Plants compete for light and so grow tall to absorb it so there is a multi-storey profile to the forests with very tall emergent trees, a canopy of others, understorey of smaller trees and shrub layer under this - called stratification. Vines, climbers and orchids live on the larger trees and use them for support (epiphytes).
In primary forest (not logged by humans, so little light reaches the forest floor that few plants can live here. Nearly all the sunlight has been intercepted before it can reach the ground. Because there are so many plant species and a stratification of them, there are many niches and habitats for animals and large mammals can get enough food. Plants have shallow roots as most nutrients are near the surface so they have buttress roots to support them.
41
What is the net productivity in a tropical rainforest
Estimated to produce 40% of NPP of terrestrial ecosystems. Growing season all year round, fast rate of decomposition and respiration and photosynthesis.
Plants grow faster. But respiration is also high and for a large mature tree in the rainforest, all the glucose made in photosynthesis is used in respiration so there is no net gain. However, when rainforest plants are immature, their growth rates are huge and biomass gain very high. Rapid recycling of nutrients.
42
How is human activity influencing tropical rainforests
The problem is that more than 50% of the world's human population lives in the tropics and subtropics and one in eight of us live in or near a tropical rainforest. With fewer humans, the forest could provide enough resources for the population but there are now too many exploiting the forest and it does not have time to recover. This is not sustainable. In addition, commercial logging of valuable timber, eg mahogany, and clear felling to convert the land to grazing cattle all destroy the forest.
43
What issues do tropical rainforests face from humans
Logging, clear-felling, conversion to grazing. Tropical rainforests are mostly in LEDs and have been exploited for economic development.
44
What are some examples of tropical rainforests
Amazon rainforest, congo in Africa, borneo rainforest
45
What is a temperate forest
Mild climate, deciduous forest
46
Where is a temperate forest found
Between 40° and 60° North and South of the equator.
47
What are some climate and limiting factors in a temperate forest
P > E. Rainfall is 500-1500 mm per year, colder in winter. Winters freezing in some (Eastern China and NE USA), milder in western Europe due to the Gulf Stream. Temp range - 30 °C to + 30 °C. Summers cool.
48
What is the structure if a temperate forest
Fewer species than tropical rainforests. For example in Britain, oaks, which can reach heights of
30-40 m, become the dominant species of the climax vegetation. Other trees, such as the elm, beech, sycamore, ash and chestnut, grow a little less high. Relatively few species and many woodlands are dominated by one species, eg beech. In USA there can be over thirty species per km?. Trees have a growing season of 6-8 months, may only grow by about 50 cm a year.
Woodlands show stratification. Beneath the canopy is a lower shrub layer varying between 5 m (holly, hazel and hawthorn) and 20 m (ash and birch). The forest floor, if the shrub layer is not too dense, is often covered in a thick undergrowth of brambles, grass, bracken and ferns. Many flowering plants (bluebells) bloom early in the year before the taller trees have developed their full foliage. Epiphytes, eg mistletoe, mosses, lichens and algae, grow on the branches. The forest floor has a reasonably thick leaf litter that is readily broken down. Rapid recycling of nutrients, although some are lost through leaching. The leaching of humus and nutrients and the mixing by biota produce a brown-coloured soil. Well-developed food chains in these forests with many autotrophs, herbivores (rabbits, deer and mice) and carnivores (foxes). Deciduous trees give way to coniferous towards polar latitudes and where there is an increase in either altitude or steepness of slope. P > E sufficiently to cause some leaching.
49
What is the net productivity in a temperate forest
Second highest NPP after tropical rainforests but much lower than these because of leaf fall in winter so reduced photosynthesis and transpiration and frozen soils when water is limiting.
Temperatures and insolation lower in winter too as further from the Sun.
50
How are humans affecting temperate forests
Much temperate forest has been cleared for agriculture or urban developments. Large predators (wolves, bears] virtually wiped out.
51
What issues do temperate forests face
Most of Europe's natural primary deciduous woodland has been cleared for farming, for use as fuel and in building, and for urban development. Some that is left is under threat, eg US Pacific Northwest old-growth temperate and coniferous forests. Often mineral wealth under forests is mined.
52
State an example of a temperate forest
US Pacific Northwest.
53
What is a desert
Dry areas which are usually hot in the day and cold at night as skies are clear and there is little vegetation to insulate the ground. There are tropical, temperate and cold deserts.
54
Where are deserts found
Cover 20-30% of the Earth's surface about 30 degrees North and South of the equator where dry air descends. Most are in the middle of continents. (Some deserts are cold deserts, eg the Gobi desert.] The Atacama desert in Chile can have no rain for 20 years or more. It is the driest place on Earth.
55
what are some climate and limiting factors found in a desert
Water is limiting. Precipitation less than 250 mm per year. Usually evaporation exceeds precipitation - E> P.
56
What is the structure of a desert
Few species and low biodiversity but what can survive in deserts is well-adapted to the conditions. Soils are rich in nutrients as they are not washed away. Plants are drought-resistant and mostly cacti and succulents with adaptations to store water and reduce transpiration, eg leaves reduced to spines, thick cuticles to reduce transpiration. Animals too are adapted to drought conditions. Reptiles are dominant, eg snakes, lizards. Small mammals can survive by adapting to be nocturnal (come out at night and stay in a burrow in the heat of the day, eg kangaroo rat] or reduce water loss by having no sweat glands and absorbing water from their food. There are few large mammals in deserts.
57
What is the net productivity in a desert
Both primary (plants) and secondary (animals) are low because water is limiting and plant biomass cannot build up to large amounts. Food chains tend to be short because of this.
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What is the human activity in a desert
Traditionally, nomadic tribes herd animals such as camels and goats in deserts as agriculture has not been possible except around oases or waterholes. Population density has been low as the environment cannot support large numbers. Oil has been found under deserts in the Gulf States and many deserts are rich in minerals including gold and silver.
Irrigation is possible by tapping underground water stores or aquifers so, 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 (salinization).
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What are some issues the desert is facing
Desertification - when an area becomes a desert either through overgrazing, overcultivation or drought or all of these, eg the Sahel.
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What are some examples of a desert
Sahara and Namib in Africa, Gobi in China.
61
What is a temperate grassland
Fairly flat areas dominated by grasses and herbaceous (non-woody) plants.
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Where are temperate grasslands found
In centres of continents 40-60° North of equator.
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What are some climate and limiting factors of a temperate grassland
P = E or P slightly > E. Temperature range high as not near the sea to moderate temperatures.
Clear skies. Low rainfall, threat of drought.
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What is the structure of a temperate grassland
Grasses, wide diversity. Probably not a climax community as arrested by grazing animals.
Grasses die back in winter but roots survive. Decomposed vegetation forms a mat, high levels of nutrients in this. Burrowing animals (rabbits, gophers), kangaroo, bison, antelopes. Carnivores wolves, coyotes. No trees.
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What is the net productivity in a temperate grassland
600 g m ? yr ' so not very high.
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What is the human activity in a temperate grassland
Used for cereal crops. Cereals are annual grasses. Black earth soils of the steppes rich in organic matter and deep so ideal for agriculture. Prairies in North America are less fertile soils so have to add fertilizers. Called world's bread baskets. Plus livestock - cattle and sheep that feed on the grasses.
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What are some issues faced in a temperate grassland
Dust Bowl in 1930s in America when overcropping and drought led to soil being blown away on the Great Plains - ecological disaster. Overgrazing reduces them to desert or semi-desert.
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What are some examples of a temperate grassland
North American prairies, Russian steppes in Northern hemisphere; pampas in Argentina, veld in South Africa (30-40° South).
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What is a artic tundra
Cold, low precipitation, long, dark winters. 10% of Earth's land surface. Youngest of all the biomes as it was formed after the retreat of the continental glaciers only 10,000 years ago.
Permafrost (frozen soil) present and no trees.
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Where are artic tundras found
Just south of the Arctic ice cap and small amounts in Southern hemisphere. (Alpine tundra is found as isolated patches on high mountains from the poles to the tropics.)
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What are some climate and limiting factors in a artic tundra
Cold, high winds, little precipitation. Frozen ground (permafrost). Permafrost reaches to the surface in winter but in summer the top layers of soil defrost and plants can grow. Low temperatures so rates of respiration, photosynthesis and decomposition are low. Slow growth and slow recycling of nutrients. Water, temperature, insolation and nutrients can be
limiting.
In the winter, the Northern hemisphere, where the Arctic tundra is located, tilts away from the sun. After the spring equinox, the Northern hemisphere is in constant sunlight. For nearly three months, from late May to August, the sun never sets. This is because the Arctic regions of the Earth are tilted toward the Sun. With this continuous sun, the ice from the winter season begins to melt quickly.
During spring and summer, animals are active, and plants begin to grow rapidly. Sometimes temperatures reach 30 °C. Much of this energy is absorbed as the latent heat of melting of ice to water.
In Antarctica, where a small amount of tundra is also located, the seasons are reversed.
72
What is the structure of a artic tundra
No trees but thick mat of low-growing plants - grasses, mosses, small shrubs. Adapted to withstand drying out with leathery leaves or underground storage organs. Growing season may only be 8 weeks in the summer. Animals also adapted with thick fur and small ears to reduce heat loss. Mostly small mammals, eg lemmings, hares, voles. Predators - Arctic fox, lynx, snowy owl. Most hibernate and make burrows. Simple ecosystems with few species.
Often bare areas of ground. Low biodiversity - 900 species of plants compared with 40,000 or more in the Amazon rainforest.
Soil poor, low inorganic matter and minerals.
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What is the net productivity in a artic tundra
Very low. Slow decomposition so many peat bogs where most of the carbon is stored.
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What is the human activity in a artic tundra
Few humans but mining and oil - see oil tars. Nomadic groups herding reindeer.
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What are some issues faced by a artic tundra
Fragile ecosystems that take a very long time to recover from disruption. May take decades to recover if you even walk across it. Mining and oil extraction in Siberia and Canada destroy tundra.
Many scientists feel that global warming caused by greenhouse gases may eliminate
Arctic regions, including the tundra, forever. The global rise in temperature may damage the Arctic and Antarctic more than any other biome because the Arctic tundra's winter will be shortened, melting snow cover and parts of the permafrost, leading to flooding of some coastal areas. Plants will die, animal migrating patterns will change, and the tundra biome as we know it will be gone. The effect is uncertain but we do know the tundra, being the most fragile biome, will be the first to reflect any change in the Earth.
Very large amounts of methane are locked up in tundra ice in clathrates. If these are released into the atmosphere then huge increase in greenhouse gases (clathrates contain 3,000 times as much methane as is in the atmosphere now and methane is more than 20 times as strong a greenhouse gas as carbon dioxide).
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What are some examples of artic tundras
Siberia, Alaska.
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What is a deep ocean
The ocean and seafloor beyond continental shelves.
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Where are deep oceans found
65% of the Earth's surface. Most is abyssal plain of the ocean floor - averaging 3.5 miles deep.
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What are some climate and limiting factors found in a deep ocean
Pressure increases with depth, temperature variation decreases to a constant -2°C at depth.
Light limiting below 1,000 m - there is none.
Nutrients - low levels and low primary productivity but some dead organic matter falls to deep ocean floors.
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What is the structure of a deep ocean
Top 200 m - some light for photosynthesis so phytoplankton and cyanobacteria live here and they and algae are the main producers. They are eaten by zooplankton, fish and invertebrates, eg squid, jellyfish.
200-1,000 m deep - as pressure increases with depth, fish here are muscular and strong to resist pressure. Very little light reaches here so large eyes, reflective sides and light-producing organs on their bodies. Many are red which absorbs shorter wavelengths of light that penetrate further.
1,000-4,000 m deep - higher diversity here, always dark. Fish are black with small eyes, bristles and bioluminescence - create own light to hunt or avoid predators. Very little muscle, large mouths.
4,000 m to bottom - huge pressures, constant cold. Mostly shrimps, some fish, jellyfish, tubeworms on bottom.
Bottom surface - fine sediments made up of debris from above - plankton shells, dead organisms, whale and fish skeletons. Also mud and volcanic rocks in mid-ocean ridges.
Where volcanoes erupt, there are hydrothermal vent communities high in sulphides where chemosynthetic bacteria gain their energy from the sulphur. These producers support communities of crabs, tubeworms, mussels, and even octopus and fish.
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What is the net productivity in a deep ocean
Low
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What is the human activity in a deep ocean
Minimal but rocks rich in manganese and iron could be a resource.
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What are some issues facing the deep ocean
Pollution from run-off from rivers, sewage, ocean warming due to climate change.
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What are some examples of deep oceans
Arctic, Atlantic, Pacific Oceans.
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LOOK AT COMPARISON OF BIOMES PAGE 113
86
What is the difference between succession and zonation
Succession is how an ecosystem changes in time.
Zonation is how an ecosystem is changing along an environmental gradient, eg altitude.
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What are the most important ecological niches in zonation
• Temperature - which decreases with increasing altitude and latitude.
• Precipitation - on mountains, most rainfall is at middle altitudes so deciduous forest grows. Higher up, the air is too dry and cold for trees.
• Solar insolation - more intense at higher altitudes and plants have to adapt - often with red pigment in their leaves to protect themselves against too much insolation.
• Soil type - in warmer zones, decomposition is faster so soils are deeper and more fertile. Higher up, decomposition is slow and soils tend to be acidic.
• Interactions between species - competition may crowd out some species and grazing may alter plant composition. Mycorrhizal fungi (2.1) may be very important in allowing trees to grow in some zones.
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How does human activities alter zonation
Human activities alter zonation. Road building on mountains may allow tourism into previously inaccessible areas or deforestation or agriculture.
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LOOK AT KITE DIAGRAM PAGE 116
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Define primary succession
Primary succession occurs on a bare inorganic surlace. It involves the colonization of newly created land by organisms. It occurs as new land is either created or uncovered such as river deltas, after volcanic eruptions, on sand dunes.
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What is an example of succession
Bare land almost anywhere on the planet does not stay bare for very
species, biodiversity.
long. Plants very quickly start to colonize the bare land and over time an entire plant community develops. This change is directional as one community is replaced by another. This process is succession. Succession results in a natural increase in complexity to the structure and species composition of a community over time.
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What are the 6 stages of succession
1. Bare inorganic surface
2. Stage 1 colonisation
3. Stage 2 establishment
4. Stage 3 competition
5. Stage 4 stabilisation
6. Climax community
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What is a bare inorganic surface
A lifeless abiotic environment becomes available for colonization by pioneer plant and animal species. Soil is little more than mineral particles, nutrient poor and with an erratic water supply.
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What happens in stage 1 colonisation
First species to colonize an area are called pioneers adapted to extreme conditions.
Pioneers are typically r-selected species showing small size, short life cycles, rapid growth and production of many offspring or seeds.
Simple soil starts from windblown dust and mineral particles.
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What happens in stage 2 establishment
Species diversity increases. Invertebrate species begin to visit and live in the soil increasing humus (organic material] content and water-holding capacity. Weathering enriches soil with nutrients.
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What happens in stage 3 competition
Microclimate continues to change as new species colonize. Larger plants increase cover and provide shelter, enabling K-selected species to become established. Temperatures, sun and wind are less extreme. Earlier pioneer r-species are unable to compete with K-species for space, nutrients or light and are lost from the community.
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What happens in stage 4 stabilisation
Fewer new species colonize as late colonizers become established shading out early colonizers. Complex food webs develop.
K-selected species are specialists with narrower niches. They are generally larger and less productive (slower growing) with longer life cycles and delayed reproduction.
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What happens in the climax community
The final stage or climax community is stable and self-perpetuating. It exists in a steady-state dynamic equilibrium. The climax represents the maximum possible development that a community can reach under the prevailing environmental conditions of temperature, light and rainfall.
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What are the stages of hydrosere (succession in water)
1. deep freshwater, no rooted plants because of lack of light in deep water
2. community only microorganisms and phytoplankton
3. sediments get carried into the pond allowing rooted submerged and floating plants to start to grow
4. sediments continue to build up
5. reeds and grasses develop around pond margin, trapping more sediment
6. a marsh community builds up around the pond margins
7. reeds take over more of the ponds as more silt builds up
8. as the soil around the edge dries from waterlogged to damp, tree species such as willow and alder become established
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What leads to the creation of a climax community in ponds and lakes
Ponds and lakes get continuous inputs of sediment from streams and rivers that open into them. Some of this sediment passes through but a lot sinks to the pond bottom. As plant communities develop they add dead organic material to these sediments. Over time these sediments build up allowing rooted plants to invade the pond margins as the pond slowly fills in. This eventually leads to the establishment of climax communities around the pond margins and in smaller ponds the eventual disappearance of the pond.
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What is secondary succession
Where an already established community is suddenly destroyed, such as following fire or flood or even human activity (plowing) an abridged version of succession occurs.
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Where does secondary succession occur
This secondary succession occurs on soils that are already developed and ready to accept seeds carried in by the wind. Also there are often dormant seeds left in the soil from the previous community. This shortens the number of stages the community goes through.
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What changes occur during succession
• The size of organisms increases with trees creating a more hospitable environment.
• Energy flow becomes more complex as simple food chains become complex food webs.
• Soil depth, humus, water-holding capacity, mineral content and cycling all increase.
• Biodiversity increases because more niches (lifestyle opportunities)
appear and then falls as the climax community is reached.
• NPP and GPP rise and then fall.
• Productivity : respiration ratio falls.
104
How does primary productivity vary with time
Primary productivity varies with time. When plants first colonize bare ground, it is low as there are not many plants and they are starting from a seed. It rises quickly as more plants germinate and the biomass accumulates. When a climax community is reached (stable community of plant and animal species), productivity levels off as energy being fixed by the producers is approximately equal to the rate at which energy is being used in respiration, and emitted as heat.
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Why is gross primary productivity low in early stages
In the early stages, gross primary productivity is low due to the initial conditions and low density of producers. The proportion of energy lost through community respiration is relatively low too, so net productivity is high, ie the system is growing and biomass is accumulating.
106
When does gross productivity start to rise
In later stages, with an increased producer, consumer and decomposer community, gross productivity continues to rise to a maximum in the climax community. However, this is balanced by equally high rates of respiration particularly by decomposers, so net productivity approaches zero and the productivity : respiration (P:R) ratio approaches 1.
107
During succession when does gross primary productivity start to increase
During succession, gross primary productivity tends to increase through the pioneer and early stages and then decreases as the climax community reaches maturity. This increase in productivity is linked to growth and biomass.
108
In early stages of succession is gross primary productivity high or net primary productivity
Early stages are usually marked by rapid growth and biomass accumulation - grasses, herbs and small shrubs. Gross primary productivity is low but net primary productivity tends to be a large proportion of GPP as with little biomass in the early stages, respiration is low. As the community develops towards woodland and biomass increases so does productivity. But NPP as a percentage of GPP can fall as respiration rates increase with more biomass.
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How does species diversify with succession
In early stages of succession, there are only a few species within the community. As the community passes through subsequent stages so the number of species found increases. Very few pioneer species are ever totally replaced as succession continues. The result is increasing diversity - more species. This increase tends to continue until a balance is reached between possibilities for new species to establish, existing species to expand their range and local extinction.
Evidence following the eruption of the Mount St Helens volcano in 1980 has provided ecologists with a natural laboratory to study succession. In the first 10 years after the eruption species diversity increased dramatically but after 20 years very little additional increase in the diversity occurred.
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How does succession occur in Dorset sand dunes
This begins with a bare surface of sand. Vegetation colonizes the sand. The pioneer plants tend to be low growing - why? They have fat fleshy leaves with a waxy coating and are able to survive being submersed - temporarily.
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How does vegetation add to succession on Dorset sand dunes
Later, the predominant plant species is marram grass on the seaward side due to its ability to cope with the environmental conditions. It, like the other grasses, have leaves which are able to fold to reduce its surface area. Leaves are waxy to reduce transpiration and can be aligned to the wind direction. It incorporates silica into its cell structure to give the leaves extra strength and flexibility.
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How does the sandy soil help succession on Dorset sand dunes
As a result of the humus from the previous stages, a sandy soil has now developed. This is now able to support 'pasture' grasses and bushes. Species such as hawthorn, elder, brambles and sea buckthorn (which has nitrogen-fixing root nodules so can thrive in nutrient-poor soil) are present. As the scrub develops, shorter species will be shaded out.
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What do the oldest sand dunes have
The oldest dunes will have forest - first pine and finally oak and ash woodland growing on them; the climatic climax vegetation for the area. Here the species diversity declines due to competition - for what?
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What happens in the final stages of succession on Dorset sand dunes
In every case, vegetation colonizes in a series of stages. The final one is in dynamic equilibrium with its climatic environment and hence is known as climatic climax vegetation. In the UK this is temperate deciduous forest. As succession develops, there are increases in vegetation cover, soil depth and humus content, soil acidity, moisture content and sand stability.
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How can succession be stopped
Succession may be stopped or 'arrested' at a stage by an abiotic factor, eg soil conditions such as waterlogging, or a biotic factor such as heavy grazing. This results in an arrested or sub-climax community which will only continue its development if the limiting factor is removed.
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what can affect a climax community
Under other circumstances a climax community may be affected by either a natural event, eg fire or landslide, or human activity such as agriculture, regular use of fire or habitat destruction. This will lead to a deflected or plagioclimax community such as pasture, arable farmland or plantations with reduced biodiversity. Again if the human activity ceases the plagioclimax community will develop into the climatic climax community.
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What are the significant changes during succession
During succession energy flow, gross and net productivity, diversity and mineral cycling change. In early stages gross productivity is low due to the initial conditions and low density of producers. The proportion of energy lost through community respiration is relatively low too, so net productivity is high, ie the system is growing and biomass is accumulating. In later stages, with an increased consumer community, gross productivity may be high in a climax community. However, this is balanced by respiration, so net productivity approaches zero and the productivity : respiration (P:R) ratio approaches 1. Biodiversity increases during succession as more species arrive and then decreases slightly if a stable climax community is reached. Mineral cycling tends to be slow at the early stages of succession but increases strongly during the succession process.
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What is the conflict between natural succession and human requirements for agriculture
There is a basic conflict between natural succession and human requirements in agriculture. We want to achieve high rates of productivity with no standing crop left. The natural system leads to increasing complexity, longer food chains, higher biodiversity, more biomass and a well-organized stratified ecosystem. Food production aims for a simple system where weed plants are controlled and monoculture maximizes vield that does not reach a climax community. But we have not placed a value on other services - natural income that natural systems provide - a balance in the carbon cycle, nutrient cycling, climate buffer of forests and oceans, clean water provision, aesthetic services that natural systems provide. Less productive places are as necessary as productive fields. We need waste places, a mixture of habitats, quality as well as quantity. While we may be able to grow crops on more land, should we? What is the balance between human rights and environmental rights that we need to find?
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What are k and r strategists
Species can be roughly divided into K- and r-strategists or K- and r-selected species. K and r are two variables that determine the shape of the population growth curve. K is the carrying capacity and r describes the shape of the exponential part of the growth curve.
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What are the characteristics of r strategists
Short life
Rapid growth
Early maturity
Many small offspring
Little parental care or protection
Little investment in individual offspring
Adapted to unstable environment
Pioneers, colonizers
Niche generalists
Prey
Regulated mainly by external factors
Lower trophic level
Examples: annual plants, flour beetles,
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What are the characteristics of k strategists
Long life
Slower growth
Late maturity
Fewer large offspring
High parental care and protection
High investment in individual offspring
Adapted to stable environment
Later stages of succession
Niche specialists
Predators
Regulated mainly by internal factors
Higher trophic level
Examples: trees, albatrosses, humans
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What is a survivorship curve
A survivorship curve shows the fate of a group of individuals of a species. Three hypothetical survivorship curves are shown in figure 2.4.30. Note that the vertical axis is logarithmic.
