Ecology Final Exam (22, 23, 24, 25, 27)

Whereas we classify terrestrial ecosystems according to their dominant plant lifeforms, the classification of aquatic ecosystems is largely based on features if the physical environment.

A major feature influencing the adaptations of organisms to the aquatic environment is water salinity. For this reason, aquatic ecosystems fall into two major categories: freshwater and saltwater (marine). These categories are further divided into several ecosystem types based on substrate, depth and flow of water, and type of dominant organisms (typically autotrophs).

Conifer forests dominate the cool temperate and boreal zones:

Conifer forests, dominated by needle-leaf evergreen trees, are found primarily in a broad circumpolar belt across the Northern Hemisphere and on mountain ranges, where low temperatures limit the growing season to a few months each year. The variable composition and structure of these forests reflect the wide range of climatic conditions in which they grow.

Sedimentary cycles:

In sedimentary cycles, the main pool is the soil, rocks, and minerals. The mineral elements required by living organisms come initially from inorganic sources... Available forms occur as salts dissolved in soil water or in lakes, streams, and seas. The mineral cycle varies from one element to another, but essentially it consists of two phases: the rock and the salt solution phase.

Adaptations to slow-moving streams:

In slow-flowing streams where current is at a minimum, streamlined forms of fish give way to species such as smallmouth bass, whose compressed bodies enable them to move through beds of aquatic vegetation. Pulmonate snails and burrowing mayflies replace rubble-dwelling insect larvae. Bottom-feeding fish, such as catfish, feed on life on the silty bottom, and back-swimmers and water striders inhabit sluggish stretches and still backwaters.

Predominant climate features of the temperate grasslands:

Natural grasslands occupy regions where rainfall is low, but they are not exclusively climatic. Many exist through the intervention of fire and human activity - conversions of forests into agricultural lands and the planting of hay and pasturelands extended grasslands into once forested regions... The natural grasslands of the world occur in the midlatitudes in the middle of continental regions, where annual precipitation declines as air masses move inwards away from the coastal environments. These regions include the prairies of North America.

The nitrogen cycle begins with the fixing of atmospheric nitrogen:

Nitrogen is an essential constituent of protein, which is a building block of all living tissue. Nitrogen is generally available to plants in only two chemical forms: ammonium and nitrate. Thus, although Earth's atmosphere is almost 80% nitrogen gas, it is in a form (N2) that is not available for uptake or assimilation by plants.

Ponds/lakes may be divided into both vertical and horizontal strata, based on light penetration and photosynthetic activity.

The horizontal zones are obvious to the eye, but the vertical strata are influenced by depth of light penetration, and are not.

Nutrients enter the ecosystem via inputs:

The input of nutrients to the ecosystem depends on the type of biogeochemical cycle. Nutrients with a gaseous cycle, such as carbon and nitrogen, enter the ecosystem via the atmosphere. In sedimentary cycles, inputs depend on the weathering of rocks and minerals... The process of soil formation and the resulting soil characteristics have a major influence on processes involved in nutrient release and retention.

Review of inputs:

The input of nutrients to the ecosystem depends on whether the biogeochemical cycle is gaseous or sedimentary. The availability of essential nutrients in terrestrial ecosystems depends heavily on the nature of the soil. Supplementing the nutrients in soil are the nutrients carried by rain, snow, air currents, and animals. The major sources of nutrients for aquatic life are inputs from the surrounding land in the form of drainage water, detritus, and sediments.

All biogeochemical cycles share 3 basic components:

inputs internal cycling outputs

The sedimentary cycles involve two phases:

salt solution & rock. Minerals become available through the weathering of Earth's crust, enter the water cycle as salt solution, take diverse pathways through the ecosystem, and ultimately return to Earth's crust through sedimentation. All nutrient cycles have a common structure and share three basic components: inputs, internal cycling, and outputs.

Describe lake origins:

(1) Glaciation - Some lakes have formed through glacial erosion and deposition. Glaciers can carve basins that fill with water from rain/melting snow. Retreating glaciers left behind crescent-shaped ridges of rock debris (moraines) which dammed up water behind them. (2) Natural dams (Debris, silt, landslides) - Lakes can also from when silt, driftwood, and other debris deposited in beds of slow-moving streams dam up water behind them. Loops of streams that flow over flat floodplains are often cut off by sediments, forming lakes. Landslides may block streams and valleys to form new lakes/ponds. (3) Geologic activity-depressions - Shifts in Earth's crust, uplifting mountains, or displacing rock strata, sometimes develop water-filled depressions. (4) Volcanic craters - Craters of some extinct volcanoes have also become lakes. (5) Beaver dams - Beavers dam streams to make shallow but extensive ponds. (6) Human dams - Humans create huge lakes by damming rivers and streams for power, irrigation, or water storage and construct smaller ponds and marshes for recreation, fishing, and wildlife. (7) Quarries and surface mines can also form ponds.

Lakes have well-defined physical characteristics:

(1) Light penetration (2) Temperature stratification (3) Oxygen stratification These physical characteristics strongly influence the distribution and adaptations of life in lakes and ponds.

Flowing-water ecosystems often alternate between two different but related habitats:

(1) Riffle - Sites of primary production; Periphyton (organisms that are attached to or move on submerged rocks and logs) assume dominance. (2) Pool - Sites of decompositions; Above and below the riffles are the pools. The environment differs in chemistry, intensity of current, and depth. Here, the velocity of the current slows enough for organic matter settle. Processes occurring in the rapids influence the waters of the pools below, and in turn, the waters of the rapids are influenced by events in the pools upstream. Without pools, photosynthesis in the riffles would deplete the bicarbonates and result in smaller quantities of available carbon dioxide downstream.

Invertebrate inhabitants are classified into 4 major groups based on their feeding habits:

(1) Shredders (2) Filtering collectors and Gathering collectors (3) Grazers (4) Gougers

Conditions unique to the Arctic tundra are a product of at least 3 interacting forces:

(1) the permanently frozen deep layer of permafrost (2) the overlying active layer of organic matter and mineral soil that that's each summer and freezes the following winter (3) vegetation that reduces warming and retards thawing in summer. Permafrost chills the soil, retarding the general growth of plant parts both above and below ground, limiting the activity of soil microorganisms and diminishing the aeration and nutrient content of the soil.

Predominant plant growth of conifer forests:

*Dominated by evergreen trees* In North America, several coniferous forests blanket the Rocky, Wasatch, Sierra Nevada, and Cascade mountains. At high elevations, grows a subalpine forest of dominated by Engelmann spruce and subalpine fir. Middle elevations have stands of Douglas fir, and lower elevations are dominated by open stands of pine and dense stands of conifer, lodgepole pine. The largest tree of all, the giant sequoia, grows in scattered groves on the western slopes of the California Sierra. In addition, the mild, moist climate of the Pacific Northwest supports a highly productive coastal forest extending from Alaska to Northern California. In North America, the boreal forest covers much of Alaska and Canada and spills into northern New England with fingers extending into the Appalachians.

Predominant plant growth and adaptations of the temperate grasslands:

- 50% of biomass is allocated to the roots. - The most visible feature of grassland is the tall, green, ephemeral herbaceous growth that develops in spring and dies back in autumn. - The highly developed root layer can make up more than half of the total plant biomass and typically extends fairly deep into the soil. - Depending on their history of fire and degree of grazing and mowing, grasslands accumulate a layer of mulch that retains moisture and, with continuous turnover of fine roots, add organic matter to the mineral soil.

Deserts represent a diverse group of ecosystems:

- Evaporation exceeds rainfall - Low humidity - Very sparse organic matter Deserts represent a diverse group of ecosystems. Temperate deserts lie in the rain shadow of mountain barriers or are located far inland, where moist maritime air rarely penetrates. Here, temperatures are high during the summer but can drop to below freezing during the winter months, Thus, the lack of precipitation, rather than continually high temperature, is the distinctive characteristic of all deserts.

Tropical rain forests:

- High diversity - Broadleaf evergreen - aseasonal - ultisoils - little litter accumulation/ high rates of decomposition - nutrient poor soils and internal form photoperiod - 5 distinct vertical layers: emergent trees, upper canopy, lower canopy, shrub understory, and a ground layer of herbs and ferns. - Buttresses - roots that support trees in shallow soil - shallow nutrient cycling

**Summary of temperate grasslands:

- Natural grasslands occupy regions where rainfall is relatively low. Natural grasslands have shrunk to a fraction of their original size because of conversion to cropland and grazing lands. - Grasslands vary with climate and geography. Native grassland of North America, influenced by declining precipitation from eats to west, consist of tallgrass prairie, mixed-grass prairie, shortgrass prairie, and desert grasslands. - Grassland consists of an ephemeral herbaceous layer that arises from crowns, nodes, and rosettes of plants hugging the ground. It also has a ground layer and a highly developed root layer. Depending on the history of fire and degree of grazing and mowing, grasslands accumulate a layer of mulch. - Grasslands support a diversity of animal life dominated by herbivorous species, both invertebrate and vertebrate. Grasslands once supported herds of large grazing ungulates such as bison in North America. Grasslands evolved under the selective pressure of grazing. Although the most conspicuous grazers are large herbivores, the major consumers are invertebrates. The heaviest consumption takes place belowground, where the dominant herbivores are nematodes.

Tropical dry forests:

- Undergo a dry season whose length is based on latitude. - The more distant the forest is from the equator, the longer the dry season (up to 8 months of the year). - During the dry season, the drought-deciduous trees and shrubs drop their leaves. Before the start of the rainy season, which may be much wetter than the wettest time in the rain forest, the trees begin to lead. During the wet season, the landscape becomes uniformly green.

Predominant climate features of the conifer forest:

A cold continental climate with strong seasonal variation dominates the conifer forests. The summers are short, cool, and moist. The winters are long, harsh, and dry with prolonged periods of snowfall. Much of the taiga is under controlling influence of permafrost, which impedes infiltration and maintains high soil moisture.

Watershed:

An area of land that drains into a lake, pond, stream, or river. Inputs of nutrients, silt and pollutants. These inputs enrich aquatic systems by the process of eutrophication (eutrophy = rich in nutrients).

Biogeochemical cycle:

All nutrients flow from the nonliving to the living and back to the nonliving components of the ecosystem in a cyclic path.

Review of how biogeochemical cycles are linked:

All of the major biogeochemical cycles are linked; the nutrients that cycle are all components of living organisms, constituents of organic matter. Stoichiometric relationships among the various elements involved in plant processes related to carbon uptake and plant growth have an important influence on the cycling of nutrients in ecosystems.

Predominant plant growth form and adaptation of the Mediterranean shrublands:

All regions of Mediterranean shrublands support similar looking communities of broadleaf evergreen shrubs and dwarf trees known as sclerophyllous - vegetation with a herbaceous understory. Sclerophyllous vegetation possesses small leaves, thickened cuticles, glandular hairs, and sunken stomata - all characteristics that function to reduce water loss during the summer periods. Vegetation in each of the Mediterranean systems also shares adaptation to fire and to low nutrient levels in the soil.

Terrestrial ecosystems reflect adaptations of the dominant plant life-forms:

Although the broad categories of grasses, shrubs, and trees each represent a diverse range of species and characteristics, they have fundamentally different patterns of carbon allocation and morphology. Grasses allocate less carbon to the production of supportive tissues (stems) than do woody plants (shrubs and trees), enabling grasses to maintain a higher proportion of their biomass in photosynthetic tissues (leaves). For woody plants, shrubs allocate a lower percentage of their resources to stems than do trees. The production of woody tissue gives the advantage of height and access to light, but it also has the associated cost of maintenance and respiration. As environmental conditions become adverse for photosynthesis (dry, low nutrient concentrations, short growing seasons, or cold temps), trees decline in both stature and density until they can no longer persist as part of the plant community.

The various biogeochemical cycles are linked:

Although we have introduced each of the major biogeochemical cycles independently, they are all linked in various ways. In specific cases, they are linked through their common membership in compounds that form an important component of their cycles (ex. links between calcium and phosphorus in mineral apatite - a phosphate of calcium - and the link between nitrogen and oxygen in nitrate). In general, cycled nutrients are all components of living organisms and constituents of organic matter. As a result, they travel together in their odyssey through internal cycling.

Carbon cycling varies daily and seasonally:

At daylight, when photosynthesis begins, plants start to withdraw carbon dioxide from the air, and the concentration declines sharply. By afternoon, when the temperature is increasing and relative humidity is decreasing, the rate of photosynthesis declines and the concentration of CO2 in the air surrounding the canopy increases. By sunset, photosynthesis ceases - carbon dioxide is no longer being withdrawn from the atmosphere - respiration increases, and the atmospheric concentration of CO2 increases sharply. Atmospheric concentrations of CO2 in the atmosphere similarly drop when photosynthesis is high due to growing seasons.

Describe how the structure of a stream/river changes with stream order:

Because streams become larger on their course to rivers and are joined along the way by many others, we can classify them according to order. A small headwater stream with no tributaries is a first-order stream. Where two streams of the same order join, the stream becomes one of the higher order. For example, of two first-order streams unite, the resulting stream becomes a second-order stream. When two second-order streams unite, the stream becomes third-order. **The order of a stream increases ONLY when a stream of the same order joins it.

Explain how biomes are classified:

Biomes are classified according to the predominant plant types. There are at least 8 major terrestrial biome types, but there may be more, depending on how finely the biomes are classified... These include tropical forest, temperate forest, conifer forest (or taiga or boreal forest), tropical savanna, temperate grasslands, chaparral (shrublands), tundra, and desert. These broad categories reflect the relative contribution of the three general plant life forms: trees, shrubs, and grasses. A closed canopy of trees characterizes forest ecosystems. Woodland and savanna ecosystems are characterized by the condominance of grasses and trees or shrubs. Shrubs are the dominant plant form in shrublands, and grasses dominate in grasslands. Desert in a general category used to refer to areas with scarce plant cover.

**Summary of temperate forests:

Broadleaf deciduous forests are found in the wetter environments of the warm temperate region. In North America, deciduous forests are still widespread, although they have been reduced by human activity. They include various types of vegetation such as beech-maple and oak-hickory forests; the greatest development is in the mixed mesophytic forest of the unglaciated Appalachians. Well-developed deciduous forests have 4 strata: upper canopy, lower canopy, shrub layer, and ground layer. Vertical structure influences the diversity and distribution of life in the forest. Certain species are associated with each stratum.

Export can occur in a variety of ways, depending on the specific biogeochemical cycle:

Carbon is exported to the atmosphere in the form of carbon dioxide via the process of respiration by all living organisms. Transport of nutrients from the ecosystem can also occur in the form of organic matter. Organic matter from a forested watershed can be carried from the ecosystem through surface flow of water in streams and rivers.

The carbon cycle is closely tied to energy flow:

Carbon, a basic constituent of all organic compounds, is involved in the fixation of energy by photosynthesis. Carbon is so closely tied to energy flow that the two are inseparable.

Predominant animal species of the conifer forests:

Caribou, moose, snowshoe hare, red squirrel, wolf, lynx, pine martin, and owls. Migratory birds.

Temperate grasslands:

Centers of continents Low annual precipitation Fire Grazing Large portion of North American grasslands is currently used for agriculture

**Summary of conifer forests:

Coniferous forests of temperate regions include the lower elevation pine forests of North America. North of temperate coniferous forest is the circumpolar taiga, or boreal forest, the largest biome on Earth... Characterized by a cold continental climate, the taiga consists of four major zones: the forest ecotone, open boreal woodland, main boreal forest, and boreal-mixed forest ecotone. Permafrost, the maintenance of which is influenced by tree and ground cover, strongly influences the pattern of vegetation, as do reoccurring fires. Spruces and pines dominate the boreal forest with successional communities of birch and polar. Ground cover below spruce is mostly moss; in open spruce and pine stands, the cover is mostly lichen. Major herbivores if the boreal region include caribou, moose, and snowshoe hare. Predators include the wolf, lynx, and pine martin.

Explain the significance of leaf dormancy:

Deciduous leaf type is further divided into two categories of dormancy period. Winter-deciduous leaves are characteristic of temperate regions, where the period of dormancy corresponds to below freezing temps. Drought-deciduous leaves are characteristic of environments with seasonal rainfall, especially in the subtropical and tropical regions, where leaves are shed during the dry period.

Summary of deserts:

Deserts are largely confined to two worldwide belts between 15 N and 30 S latitude. Deserts result from dry descending air masses within these regions, the rain shadows of coastal mountain ranges, and remoteness from oceanic moisture. Two broad types of deserts exist: cool deserts and hot deserts. Deserts are structurally simple - scattered shrubs, ephemeral plants, and open, stark topography. In this harsh environment, ways of circumventing aridity and high temperatures by either evading or resisting drought have evolved in plants and animal. Despite their aridity, deserts support a diversity of animal life, notably opportunistic herbivorous species and carnivores.

Deserts are not the same everywhere:

Differences in moisture, temperature, soil drainage, topography, alkalinity, and salinity create variations in vegetation cover, dominant plants, and groups of associated species. There are hot deserts and cold deserts, extreme deserts and semi deserts, ones with enough moisture to verge on being grasslands or shrublands, and gradations between those extremes within continental deserts.

Filtering collectors and gathering collectors:

Drifting downstream and settling on the stream bottom, the smaller fine particulate organic matter (FPOM) is picked up by the filtering collectors and gathering collectors. The filtering collectors include, among others, the larvae of black flies with filtering fans and the net-spinning cadisflies. Gathering collectors, such as the larvae of midges, pick up particles from stream-bottom sediments. Collectors obtain much of their nutrition from bacteria associated with the fine detrital particles.

**Summary of dry tropical forests:

Dry tropical forests undergo varying lengths of dry season, during which trees and shrubs drop their leaves (drought-deciduous). New leaves are grow at the onset of the rainy season. Most dry tropical forests have been lost to agriculture, grazing, and other disturbances.

Review of the global carbon cycle:

Earth's carbon budget is closely linked to the atmosphere, land, and oceans and to the mass movements of air around the planet. In the ocean, surface water acts as the main site of carbon exchange between the atmosphere and ocean. The ability of the surface waters to take up carbon dioxide is governed largely by the reaction of carbon dioxide with the carbonate ion to form bicarbonates. The uptake of carbon dioxide from the atmosphere by terrestrial ecosystems is governed by the gross production aka photosynthesis. Losses are a function of autotrophic and heterotrophic respiration; the latter are dominated by microbial decomposers.

Compare eutrophic and oligotrophic lakes:

Eutrophic lake: Rich in nutrients. A typical eutrophic lake has a high surface-to-volume ratio - that is, the surface area is large relative to depth. High NPP. Algal blooms and dense plant coverage. High decomposition rates. Oxygen deficiency is common and long term. Unhealthy! Oligotrophic lakes: Nutrient poor. Low surface-to-volume ratio. Clear water. Limited NPP (phosphorus). Nitrogen may be abundant. Oxygen deficiency is rare and short term. Healthy!

Flowing-water (lotic) ecosystems vary in structure and types of habitats:

Even the largest rivers begin as springs or seepage areas that become headwater streams, or they arise as outlets of ponds or lakes. Very few rivers emerge full formed from glaciers... As a stream drains away from its source, it flows in a direction and manner dictated by the lay of the land and the underlying rock formations. Joining the new stream re other small streams, spring seeps, and surface waters.

Explain the morphology of evergreen leaves:

Evergreen leaves can likewise be classified into two broad categories. The broadleaf evergreen leaf type is characteristic of environments with no distinct growing season where photosynthesis ad growth continue year-round, such as in tropical rainforests. The needle-leaf evergreen form is characteristic of environments where the growing season is very short (northern latitudes) or nutrient availability severely constraints photosynthesis and plant growth.

Velocity of streams:

Fast streams have stony bottoms. Slow streams have silt and organic matter on the bottom, rooted vegetation.

The major sources of nutrients for aquatic life are inputs from the surrounding land in the form of drainage water, detritus, and sediment and from the atmosphere in the form of precipitation.

Flowing-water aquatic systems (streams and rivers) are highly dependent on a steady input of dead organic matter from the watersheds they flow through.

Temperate forests:

Forest ecosystems dominate the wetter regions of the temperate zone. In North America, temperature deciduous forests reach their greatest development in the mesic forests of the central Appalachians, where the number of tree species is unsurpassed by any other temperate area in the world.

Marine ecosystems are divided into two broad categories - coastal or open-water systems.

Freshwater ecosystems are classified on the basis of water depth and flow... Flowing-water, or LOTIC, ecosystems include rivers and streams. Non-flowing water, or LENTIC ecosystems, include ponds, lakes, ad inland wetlands.

Low precipitation and cold temperatures define the artic tundra:

Frozen plain, clothed in sedges, heaths, and willows, dotted with lakes and crossed by streams.

There are two basic types of biogeochemical cycles:

Gaseous and sedimentary; This classification is based on the primary source of nutrient input into the ecosystem. Both cycles are driven by the flow of energy through the ecosystem, and both are tied to the water cycle. Water is the medium that moves elements and other materials through the ecosystem. Without the cycling of water, biogeochemical cycles would cease.

Characteristic animal species of temperate grasslands:

Grasslands support a diversity of animal life dominated by herbivorous species, both invertebrate and vertebrate. Large grazing ungulates and burrowing mammals are the most conspicuous vertebrates. The North American grasslands were once dominated by huge migratory herds of bison and forb-consuming pronghorn antelope. The most common burrowing rodent was the prairie dog, which along with gophers and the mound-building harvester ants, appeared to be instrumental in developing and maintaining the ecological structure of the shortgrass prairie.

Predominant plant growth and animal species of the temperate deciduous forest:

Highly developed, unevenly aged deciduous forest usually have four vertical layers or strata. The upper canopy consists of the dominant tree species, below which is the lower tree canopy or understory. Next is the shrub layer, followed finally by the ground layer of herbs, ferns, and mosses. The diversity of animal life is associated with this vertical stratification and the growth forms of plants. Some animals, particularly forest anthropods, spend most of their lives in a single stratum; others range over two or more strata. Many animals - the soil and litter invertebrates in particular - remain in the subterranean stratum. Others, such as mice, shrews, ground squirrels, and forest salamanders, burrow into the soil or litter fore shelter and food. Larger mammals live on the ground and feed on herbs, shrubs, and low trees. Birds move freely among several strata but typically favor one.

Describe how human inputs of nitrogen alter the nitrogen cycle:

Human activity has significantly influenced the global nitrogen cycle... Major human sources of nitrogen input are agriculture, industry, and automobiles; in recent decades, anthropogenic inputs of nitrogen into aquatic and terrestrial ecosystems have been a growing cause of concern.

Gaseous cycles:

In gaseous cycles, the main pools of nutrients are the atmosphere and the oceans. For this reason, gaseous cycles are distinctly global. The gases most important for life are nitrogen, oxygen, and carbon dioxide. These 3 gases are the dominant component's of Earth's atmosphere.

Characteristic animal species of Mediterranean shrublands:

In north America, chaparral ad sagebrush communities support mule deer, coyotes, a variety of rodents, jackrabbits, and sage grouse.

Describe the physical structure of streams and rivers:

Just below its source, the stream may be small, straight, and swift with waterfalls and rapids. Farther downstream, where the gradient is less steep, velocity decreases and the stream begins to meander, depositing its load of sediment as silt, sand, or mud. At flood time, a stream drops its load of sediment on surrounding level land, over which floodwaters spread to form floodplain deposits. Where a stream flows into a lake or river into the sea, the velocity is suddenly checked. The river is then forced to deposit its load of sediment in a fan-shaped area about its mouth to form a delta. Here, its course is carved into several channels, which are blocked or opened with subsequent deposits.

Lakes/ponds:

Lakes and ponds are inland depressions containing standing water. Ponds are small bodies of water so shallow that rooted plants can grow over much of the bottom. Some lakes are so large that they mimic marine environments. Most ponds and lakes have outlet streams, and both may be more less temporary features on the landscape.

Explain the significance of leaf form:

Leaves can be classified into two broad categories based on their longevity. Leaves that live for only a single year or growing season are classified as deciduous, whereas those that live beyond a year are called evergreen. The deciduous leaf is characteristic of environments with a distinct growing season. Leaves are typically shed at the end of the growing season and then regrown at the beginning of the next.

Light penetration:

Life in still-water ecosystems (lentic) depends on light. The amount of light penetrating the water is influenced by natural attenuation, by silt and other material carried into the lake, and by the growth of phytoplankton.

Discuss physical and biological characteristics of the major lake zones (vertical strata): littoral, limnetic, profundal, and benthic:

Littoral zone - Most diverse; surrounding most lakes/ponds and engulfing some ponds completely is the littoral zone (or shallow water zone) in which light reaches the bottom, stimulating the growth of rooted plants. Limnetic zone - (open water to depth of light penetration; compensation level) Beyond the littoral zone is open water, the limnetic zone, which extends to the depth of light penetration. Inhabiting this zone are microscopic phytoplankton and zooplankton as well as nekton (free swimming organisms, such as fish). Profundal zone - No photosynthesis occurs. Beyond the depth of effective light penetration is the profundal zone. Its beginning is marked by the compensation depth of light, the point at which respiration balances photosynthesis. The profundal zone depends on a rain of organic material from the limnetic zone for energy. Benthic zone - (Detrital food chain, affected by stratification of oxygen, periphyton - organisms attached to/move on a submerged substrate but do not penetrate it)Common to both the littoral and profundal zone is the third vertical stratum - the benthic zone or bottom region, which is the primary place of decomposition.

Mediterranean Shrublands:

Mediterranean climates support temperate shrublands. Shrublands (plant communities where tee shrub growth form is either dominant or codominant) are difficult types of ecosystems to categorize... A shrub is a plant with multiple woody, persistent stems but not central trunk and a height from only 4.5 to 8m.

Review of outputs:

Nutrient levels within an ecosystem can decline as a result of nutrient export. Export can occur in a variety of ways, depending on the specific biogeochemical cycle. A major means of transportation is in the form of organic matter carried by surface flow of water in streams and rivers. Leaching of dissolved nutrients from soils into surface water and groundwater also represents a significant export in some ecosystems. Harvesting of biomass in forestry and agriculture represents a permanent withdrawal from the ecosystem. Fire is also a major source of nutrient export in some terrestrial ecosystems.

Review of biogeochemical cycles:

Nutrients flow from the living to the nonliving components of the ecosystem and back in a perpetual cycle. Through these cycles, plants and animals obtain nutrients necessary for their survival and growth. There are two basic types of biogeochemical cycles: the gaseous cycle, represented by oxygen, carbon, and nitrogen cycles, whose major pools are in the atmosphere, and the sedimentary cycle, represented by the sulfur and phosphorus cycles, whose major pools are in the Earth's crust.

Review of the oxygen cycle:

Oxygen (the by-product of photosynthesis) is very active chemically. It combines with a wide range of chemicals in Earth's crust, and it reacts spontaneously with organic compounds and reduced substances. It is involved in oxidizing carbohydrates in the process of respiration to release energy, carbon dioxide, and water. The current atmospheric pool of oxygen is maintained in a dynamic equilibrium between the production of oxygen in photosynthesis and its consumption in respiration. An important constituent of the atmospheric reservoir of oxygen is ozone (O3).

Oxygen stratification:

Oxygen can be limiting, especially in summer, because only a small proportion of the water is in direct contact with air, and respiration by decomposers on the bottom consumes large quantities of oxygen.

In marine and freshwater ecosystems, the phosphorus cycle moves through 3 states:

Particulate organic phosphorus, dissolved organic phosphates, and inorganic phosphates.

The main reservoirs of phosphorus are rock and natural phosphate deposits.

Phosphorus is released from these rocks and minerals by weathering, leaching, erosion, and mining for use as agricultural fertilizers. Nearly all of the phosphorus in terrestrial ecosystems comes from the weathering of calcium phosphate minerals. In most soils, only a small fraction of the total phosphorus is available to plants. The major process of regulating phosphorus availability for net primary production is the internal cycling of phosphorus from organic to inorganic forms. Some of the available phosphorus in terrestrial ecosystems escapes and is exported to lakes and seas.

The phosphorus cycle has no atmospheric pool:

Phosphorus occurs in only minute amounts in the atmosphere. Therefore, the phosphorus cycle can follow the water cycle only part of the way - from land to sea... Because phosphorus lost from the ecosystem in this way is not returned via the biogeochemical cycle, phosphorus is in short supply under undisturbed natural conditions. The natural scarcity of phosphorus in aquatic ecosystems is emphasized by the explosive growth of algae in water receiving heavy discharges of phosphorus rich waste.

Supplementing nutrients in the soil are nutrients carried by rain, snow, air currents and animals...

Precipitation brings appreciable quantities of nutrients, called wetfall. Some nutrients are brought in by airborne particles and aerosols, collectively called dryfall.

***Summary of tropical rain forests:

Rain forests, associated with high seasonal rainfall, are dominated by broadleaf evergreen trees. They are noted for their enormous diversity of plant and animal life. The vertical structure of the forest is divided into 5 general layers: emergent trees, high upper canopy, low tree stratum, shrub understory, and a ground layer of herbs and shrubs. Conspicuous in the rain forest are the lianas or climbing veins, epiphytes growing up in the trees, and stranglers growing downward from the canopy to the ground. Many large trees develop buttresses for support... Nearly 90% of nonhuman primate species live in the tropical rain forests. Tropical rain forests support higher levels of primary productivity. The high rainfall and consistently warm temperatures also result in high rates of decomposition and nutrient cycling.

***Summary of tropical forests:

Seasonality of rainfall determines the types of tropical forests: tropical rain forest or dry tropical forest.

Explain the processes involved in carbon cycling:

Several processes, particularly the rates of primary productivity and decomposition, determine the rate at which carbon cycles through the atmosphere. Both processes are influenced strongly by environmental conditions such as temperature and precipitation. *In warm, wet ecosystems such as the tropical rain forest, production and decomposition rates are high and carbon cycles through the ecosystem quickly. The process is slower in cool/dry ecosystems.

Shredders:

Shredder such as cadisflies and stoneflies make up a large group of insect larvae. They feed on course particulate organic matter (CPOM) - mostly leaves that fall into the stream. Shredders break down the CPOM, feeding on the material not so much for the energy it contains as for the bacteria and fungi growing on it.

**Summary of shrublands:

Shrubs have a densely branched, woody structure and low height. Shrublands are difficult to classify because of the variety of climates in which shrubs can be a dominant or codominant component of the plant community. Along the western margins of the continents between 30-40 degrees latitude are the found the Mediterranean ecosystems. Dominated by evergreen shrubs and sclerophyll trees, these biomes have adapted to the distinctive climate of summer drought and cool, moist winters. These shrublands are fire adapted and highly flammable.

Predominant plant growth of the tundra:

Structurally, the vegetation of the tundra is simple. The number of species tends to be low, and growth is slow. Only those species able to withstand constant disturbance of the soil, buffeting by the wind, and abrasion from wind-carried particles of soil and ice can survive. Low ground is covered with a complex of cotton grasses, sedges, and Sphagnum. Well-drained sites support heath shrub, dwarf willows, and birches, herbs, mosses, and lichens. The driest and most exposed sites support scattered heaths and curstose and foliose lichens growing on the rock. Arctic plants propagate themselves almost entirely by vegetative means, although viable seeds many hundreds of years old exist in the soil.

Review of the sulfur cycle:

Sulfur has both gaseous and sedimentary phases. Sedimentary sulfur comes from the weathering of rocks, runoff, and decomposition of organic matter. Sources of gaseous sulfur are decomposition of organic matter, evaporation of oceans, and volcanic eruptions.

Temperature stratification:

Temperatures vary seasonally and with depth.

Predominant climate features of Mediterranean shrublands:

The Mediterranean climate has hot, dry summers, with at least one month of protracted drought, and cool, moist winters. Most annual precipitation falls during winter months. The hot/dry summer climates arise from the seasonal change in the semi permanent high-pressure zones that are centered over the tropical deserts. The persistent flow of dry air out of these regions during the summer brings several months of hot and dry weather. Fire is a frequent hazard during these periods.

Nitrogen enters the ecosystem via two pathways, and the relative importance of each varies greatly among ecosystems.

The first pathway is atmospheric deposition. This can be in wetfall - such as rain, snow, or even cloud/fog droplets - and in dryfall, such as aerosols and particulates. Nitrogen in this pathway is supplied in a form that is already available for uptake by plants. The second pathway for nitrogen to enter ecosystems is via nitrogen fixation. This fixation comes about in two ways... One is high-energy fixation. Cosmic radiation, meteorite trails, and lightning provide the high energy needed to combine nitrogen with the oxygen/hydrogen of water. The second method is biological... it is accomplished by symbiotic bacteria living in mutualistic association with plants, by free-living aerobic bacteria, and by cyanobacteria.

**Summary of the tundra:

The arctic tundra extends beyond the tree line at the far north of the Northern Hemisphere. It is characterized by low temperature, low precipitation, a short growing season, a perpetually frozen subsurface (permafrost), and a frost-molded landscape. Plant species are few, growth forms are low, and growth rates are slow. Over much of the arctic, the dominant vegetation is cotton grass, sedge, and dwarf heaths. These plants exploit the long days of summer by photosynthesizing during the 24-hour daylight period. Most plant growth occurs underground. The animal community is low in diversity, but unique. Summer in the Arctic brings hordes of insects, providing a rich food source for shorebirds. Dominant vertebrates are lemming, Arctic hare, caribou, and musk ox. Major carnivores are the wolf, arctic fox, and snowy owl. Alpine tundras occur in the mountains of the world. They are characterized by widely flunctuating temperatures, strong winds, snow, and a thin atmosphere.

Review of global cycles:

The biogeochemical cycles of various ecosystems are linked. As such, it is important to view the biogeochemical cycles of many elements from a global perspective.

Review of the carbon cycle:

The carbon cycle is inseparable from energy flow. Carbon is assimilated as carbon dioxide by plants, consumed in the form of plant and animal tissue by heterotrophs, released through respiration, mineralized by decomposers, accumulated in standing biomass, and withdrawn into long-term reserves. Carbon cycles through the ecosystem at a rate that depends on the rates of primary productivity and decomposition. Both processes are faster in warm, wet ecosystems. In swamps and marshes, organic material stored as raw humus or peat circulates slowly, forming oil, coal, and natural gas. Similar cycling takes place in freshwater and marine environments.

Outputs represent a loss of nutrients from the ecosystem:

The export of nutrients from the ecosystem represents a loss that must be offset by inputs if a net decrease is not to occur.

Review of the nitrogen cycle:

The nitrogen cycle is characterized by the fixation of atmospheric nitrogen by mutualistic nitrogen-fixing bacteria associated with the roots of many plants, largely legumes, and cyanobacteria. Other processes are ammonification, the breakdown of amino acids by decomposer organisms to produce ammonia; nitrification, the bacterial oxidation of ammonia to nitrate and nitrates; and denitrification, the reduction of nitrates to gaseous nitrogen. The global nitrogen cycle follows the pathway of the local nitrogen cycle just described, only on a grander scale. The atmosphere is the largest pool, with comparatively small amounts of nitrogen found in the biomass and soils of terrestrial ecosystems. Major sources of nitrogen to the world's oceans are dissolved forms in the freshwater drainage from rivers and inputs in precipitation.

Review of the phosphorus cycle:

The phosphorus cycle has no significant atmospheric pool. The main pools of phosphorus are rock and natural phosphate deposits. The terrestrial phosphorus cycle follows the typical biogeochemical pathways. In marine and freshwater ecosystems, however, the phosphorus cycle moves through three states: particulate organic phosphorus, dissolved organic phosphates, and inorganic phosphates. Involved in the cycling are phytoplankton, zooplankton, bacteria, and microbial grazers. The global phosphorus cycle is unique among the major biogeochemical cycles in having no significant atmospheric component, although airborne transport of phosphorus occurs in the form of soil dust and sea spray. Nearly all of the phosphorus in terrestrial ecosystems is derived from the weathering of calcium phosphate minerals. The transfer of phosphorus from terrestrial to aquatic systems is low under natural conditions; however, the large scale application of phosphate fertilizers and the disposal of sewage and wastewater to aquatic ecosystems result in a large input of phosphorus to aquatic ecosystems.

A simple economic model has been proposed to explain the adaptation of this leaf form (the needle-leaf evergreen):

The production of a leaf has a "cost" to the plant that can be defined in terms of the carbon and other nutrients required to construct the leaf. The time required to "pay back" the cost of production (carbon) will be a function of the rate of net photosynthesis (carbon gain). If environmental conditions result in low rates of net photosynthesis, the period of time required to pay back the cost of production will be longer. If the rate of photosynthesis is low enough, it may not be possible to pay back the cost over the period of a single growing season... A plant adapted to such environmental conditions cannot afford a deciduous leaf from, which requires producing new leaves every year. The leaves if evergreens, however, may survive several years. SO under this model, we can view the needle-leaf evergreen as a plant adapted fro survival in an environment with a distinct growing season, in which conditions limit the plant's ability to produce enough carbon through photosynthesis during the growing season to pay for the cost of producing new leaves.

Explain the distribution of biomes on gradients of temperature and precipitation:

The range of observed values for mean annual precipitation declines with decreasing mean annual temperature. Mean annual temperature decreases from the equator to the poles, whereas seasonal variation in temperature increases at the poles. The result is a decline in growing season. Annual average precipitation decreases with increasing latitude as a result of the interaction of humidity and temperature. With declining temperatures, the amount of moisture that can be held in the air declines, reducing the overall precipitation.

Explain the source for carbon in the environment:

The source of all carbon, both in living organisms and fossil deposits, is carbon dioxide in the atmosphere and the waters of Earth. Photosynthesis draws carbon dioxide from the air and water into the living component of the ecosystem. Carbon passes to herbivores and then to carnivores. Primary producers and consumers release carbon back to the atmosphere in the form of carbon dioxide by respiration. The carbon in plant and animal tissues eventually goes to the reservoir of dead organic matter. Decomposers release it to the atmosphere through respiration.

Temperate grassland climate continued...

The temperature grassland climate us one of reoccurring drought, and much of the diversity of vegetation cover reflects differences in the amount and reliability of precipitation. Grasslands do the least well where precipitation is lowest and temps are high - they are tallest in stature and most productive where mean annual precipitation is greater and mean annual temp is above 15 C. Thus, native grasslands of North America, influenced by declining precipitation from east to west, consist of three main types distinguished by the height of the dominant species: tallgrass, mixed-grass, and shortgrass prairie.

Predominant climate features of the tropical rain forests:

The tropical rain forests are restricted primarily to the equatorial zone, where the temperatures are warm throughout the year and rainfall occurs almost daily. Tropical rainforests have a diversity of plant and animal life. The continually warm/moist conditions in rain forests promote strong chemical weathering and rapid leaching of soluble materials. The warm and wet conditions result in high net primary productivity and high annual rates of litter input to the forest floor - however, little litter accumulates because decomposers consume the dead organic matter almost as rapidly as it falls to the floor.

Characteristic animal species of the tundra:

The tundra hosts fascinating animal life, even though the diversity of species is low. Invertebrates are concentrated near the surface where there are abundant populations of segmented whiteworms, collembolas, and flies - chiefly crane flies. The dominant vertebrates of the arctic tundra are herbivores, including lemmings, arctic hare, caribou, and musk ox. The major arctic carnivore is the wolf, but smaller predators include the arctic fox and several species of weasel.

Predominant climate features of the temperate deciduous forest:

There is seasonality and diversity. There are 4 distinct seasons.

Gougers:

This group, associated with woody debris, are invertebrates that burrow into waterlogged limbs and trunks of fallen trees.

Interpret climate diagrams:

To help understand the relationship between regional climate and the distribution of terrestrial ecosystems, for each biome discussed, we present a map which shows its global distribution. Accompanying the map is a series of climate diagrams. The diagrams describe the local climate at representative locations around the world where a particular biome type is found.

Adaptations to fast moving water:

Unique adaptations have evolved among these organisms that help them deal with life in the current. A streamlined form, which offers less resistance to water current, is typical of many animals found in fast water. Larval forms of many insect species have extremely flattened bodies and broad, flat limbs tat enable them to cling to the undersurfaces of stones where the current is weak. The larvae of certain species of cadisflies construct protective cases of sand or small pebbles and cement them to the bottom of stones. Among the plants, water moss and heavily branched, filamentous algae cling to rocks by strong holdfasts. All animal inhabitants of fast-water streams require high, near-saturation concentrations of oxygen and moving water to keep their absorbing and respiratory surfaces in continuous contact with oxygenated water.

Rivers flow into the sea, forming estuaries:

Waters of most streams and rivers eventually drain into the sea. The place where freshwater joins saltwater is called an estuary. Estuaries are semi-enclosed parts of the coastal ocean where seawater is diluted and partially mixed with freshwater coming from the land. Here, the one-way flow of freshwater streams and rivers into an estuary meets the inflowing and outflowing saltwater tides. Oysters are filter feeders.

Grazers:

While shredders and collectors feed on detrital material, the grazers feed on the algal coating of stones and rubble. This group includes the beetle larvae, water penny, and a number of mobile caddisfly larvae. Much of the material they scrape loose enters the drift as FPOM.