ECOLOGY

Owing to the effects of the present "information age" and to the long list of bad deeds humans have inflicted upon the environment, the word ecology is becoming much more of a household word. Be this as it may, it is likely that few non-ecologists have a grasp of what ecology is. Some view it as synonymous with environmentalist and something that will restrict their "god given freedom as Americans" to do whatever they want to the earth.

Ecology comes from the Greek word oikos, meaning "house", our immediate environment, or a place to live.

In 1870, a German zoologist Ernst Haeckel defined ecology as the relations of organisms to one another and to their surroundings.

Ecology- the study of interactions among organisms and between organisms and their physical environment.

Ecology provides the insight for interpreting the consequences of our interactions with natural systems. Ecology emphasizes that everything on the planet is interconnected. We in our daily lives affect the outcome of, and are affected by, natural processes. Thus, humans are an important part of ecology.

Ecology is very broad in scope. Ecologists often classify themselves as: plant ecologists, small mammal ecologists, community ecologists, physiological ecologist, ecological geneticist, behavioral ecologist, etc... Because the scope of ecology is so broad, individual ecologists generally specialize in one or two fields. The complexities of the relationships between or among organisms and their environment is so great that it would be impossible for any one ecologist to specialize in many areas. I study passerine birds and how they are affected by their habitat- specifically landscape effects.

Some basic definitions:

Population: A group of individual organisms of the same species living in the same area.

Populations are generally defined by the scientist/ecologist doing a particular study. In the broadest sense we might be able to define a population in some genetic terms (i.e. they may be isolated behaviorally or geographically). However, in practice, populations are generally researcher defined. We may be interested in the size of the population of ducks at: 1) the Arcata Marsh Project; 2) Humboldt Bay National Wildlife Refuge; 3) Humboldt County; 4) California; or 5) the Pacific Flyway.
 
 

Community: All the living organisms found in a particular environment. Includes all the populations of different species that are living together.

-somewhat arbitrary definition that is more often than not researcher defined.

-characterized by the dominant life-form such as redwood forest or grassland.

-difficult to enumerate all of the species in a particular community

Ecosystem: A community and its environment. Includes all the interactions between living things and their physical environment.

-like populations and communities, ecosystems can have natural or researcher defined boundaries.

In ecosystems then we have both biotic (living portions of the ecosystem) and abiotic (non-living portions of the ecosystem: minerals, water, temperature, etc.) components. Both biotic and abiotic factors can influence organisms. The most blatant example of a biotic factor affecting an organisms is through predation, but parasites and diseases, food abundance, and competitors can all influence an organism. Abiotic factors such as salinity (salt content) can affect the osmoregulation of an animal and nutrients can affect growth and reproductive patterns (as many of you gardeners know).

Biosphere: all the earth's living organisms. Includes all of the communities on earth.

Ecosphere: the largest, worldwide ecosystem. Includes all the living things on earth, their interactions with each other, and their interactions with the physical environment.

Although there are different classification schemes and levels of organization in ecology, this does not imply that any one level is more important than another nor that it is removed from another. For instance, a population ecologist that is examining why a particular organism is decreasing in abundance must observe or study individuals to see what happens to them. Ecologists attempt to synthesize or integrate information about how nature works and apply it toward problems that society has defined as important.
 
 

Energy and energy flow

Energy is the capacity to do work. Organisms require energy to do biological work: growing, moving, reproducing, repairing damaged tissues, etc.

Thermodynamics- the study of energy and its transformation.

1st law of thermodynamics- energy cannot be created or destroyed, but it can be transformed from one form to another.

-organisms cannot create the energy they require to live, they capture energy from the environment.

-this involves transforming energy from one form to another.

ex) plants transform radiant energy (sunlight) into chemical energy via photosynthesis

ex) deer convert this chem. energy from plant material into other chemical forms, and into mechanical energy- walking and running.

2nd law of thermodynamics- when energy is converted from one form to another, some energy is degraded into a less usable form (usually heat) that disperses into the surroundings.

Entropy- low quality or disorganized energy. Measure of disorder or randomness

-entropy increases over time (eventually all energy will exist as low quality heat that is uniformly distributed)

-it takes energy to fight entropy- example your bedroom over time becomes more disorganized unless you take the energy to restore order

-it appears that organisms refute the second law- maintain high level of order as they grow, develop, etc. However, they can only do this with a constant input of energy. That's why plants must photosynthesize and animals must eat.

-some creationists suggest that life violates the second law of thermodynamics- it simply isn't true!!!

Ultimate source of energy for the earth- the sun!!!!!

Energy flow within the ecosphere starts with photosynthesis.

Photosynthesis- the biological process in which chemical energy from the sun is captured and transformed into chemical energy.

Chlorophyll- the photosynthetic pigment in plants that absorbs radiant energy and converts it into chemical energy. Gives plants their green color.

CO₂ + H₂0 + sunlight => Glucose + water + oxygen

-performed by plants, algae and a few bacteria

-organisms use glucose as a source of energy for other activities

Respiration- release of chemical energy in food to produce energy.

glucose + oxygen + water => CO₂ + water + energy (ATP)

Energy flow- the passage of energy through the ecosystem.

-enters via radiant energy

-some trapped by plants and converted into chem energy

-as other organisms eat the plants the energy is released through cell respiration and is used to do work

-some energy is lost as heat as it is transferred

-this places an ultimate limit on the complexity of biological communities
 
 

Three types of organisms base on how they obtain food

Producers, Consumers, Decomposers

-most communities contain all three
 
 

Producers or autotrophs- organisms that assimilate energy from either sunlight, primarily green plants or inorganic substances, such as sulfur bacteria. Auto = self, troph = nourishment)

-manufacture complex molecules from simple molecules using some outside source of energy

Consumers or heterotrophs- organisms that cannot manufacture their own food, but must eat other organisms or organic matter to survive. Hetero = other.

Heterotrophic organisms are further divided into some familiar categories.

Decomposers- break down dead organic material and use decomposition products to obtain energy.
 
 

Trophic levels- defined by the food an organism consumes. Some species consume many different kinds of foods and therefore may occupy more than one trophic level. For example a garter snake that eats grasshoppers and spiders is both a secondary and tertiary consumer.

Primary consumers or Herbivores - consume plants.

ex) cows, deer, plant feeding insects such as grasshoppers, leafhoppers, caterpillars (lepidoptera larvae)

Secondary consumers - consume primary consumers.

ex) mountain lion, spiders, pine martin, many insect eating birds

Tertiary consumers- consume secondary consumers.

ex) Red-tailed hawk, bald eagle

Diet categories

Omnivores - plant and meat eaters

ex) black bear, pigs, humans, Stellar's jays

Carnivores- meat eaters. ex) mountain lion, wolves

Parasites - eat all or part of another organism or have their offspring forage on the "host". Does not always kill the host.

Detritivores- consume dead organic matter (sometimes lumped with decomposers)

ex) earthworms, clams, termites, maggots

Food chains- sequence by which energy from food passes from one organism to another in a community.

-generally, some predictable pathways can be mapped in most communities

There are 2 basic types of food chains:

1) grazing food chains that start with

2) detritus food chains

Food web- a complex of interconnected food chains in an ecosystem.

OVERHEAD FIG. 3-8
 
 

Ecological pyramid- most energy is lost as it is transferred up the food chain.

-can discuss a pyramid of numbers, biomass, or energy

There are many inefficiencies in energy transfer between trophic levels.

1) first, not all energy available from one trophic level is taken by the next.

2) Most food energy ingested by animals is not converted into animal tissue.

a) The second law of thermodynamics states that as energy is transferred, some is lost and is no longer available.

b) A great deal of energy is used to perform work (e.g., food capture, respiration, reproductive efforts, etc..).

On average, 80-90% of the available energy is lost at each transfer (although this is quite variable).

Pyramid of numbers- generally decreases as you move up.

ex) wildebeest and lions

ex) reverse pyramids insects and trees, maggots and dead body

Pyramid of biomass- total biomass at each level

-biomass total mass or amount of living material, weigh all indiv. and add

-generally and 10 fold decrease in biomass with each trophic level

ex) 1000 kg of grass can support 100 kg of elk which can support 10 kg of wolves

Pyramid of energy- total energy content at each level.

-similar to biomass pyramids

-most food chains are short because of reduction in energy at each level

ex) large predators need large areas, Fisher 9000 ac

ex) spotted owl- 2000 ac

Productivity of ecosystems

Gross primary productivity- rate at which energy accumulates during photosynthesis.

Net primary productivity- gross productivity - respiration by plants. i.e the amount of biomass that accumulates over time.

A few examples of primary productivity might be helpful:

The ratio of net productivity to biomass (P/B) provides an index to the availability of energy to herbivores. High P/B ratios indicate that relatively little energy is accumulated in supporting tissues, whereas low ratios indicate extensive development of supporting and root tissues.

HABITAT TYPE NPP (gm^-2yr^-1) BIOMASS (kg m^-2) RATIO

Terrestrial

Tropical Forest 1800 42 42.9:1

Temperate Forest 1250 32 39.1:1

Shrubland 600 6 100:1

Temperate Grassland 500 1.5 333.3:1

Tundra and Alpine 140 0.6 233:1

Desert scrub 70 0.7 100:1

Aquatic

Open ocean 125 0.003 42000:1

Continental shelf 360 0.01 36000:1

Estuary 1800 1 1800:1

Coral Reef 2000 2 1000:1

As expected, higher P/B ratios are found in aquatic environments and they are relatively low in terrestrial communities. Among terrestrial communities mature forests have low P/B ratios while grasslands have the highest.

When you consider it, even though mature forests have the lowest P/B ratios, most of the production of forests is allocated to roots and branches; relatively little is directly available to herbivores in the form of leaves, fruits and seeds. Leaves are high in nitrogen, and seeds are high in proteins and lipids, so they are the most desirable plant parts for herbivores. Aquatic plants and grasslands, in contrast, have much more available tissue for herbivores. Not until a tree dies do the vast majority of its tissues become available in the food chain - to detritus feeders.

Typical values for the percentage of NPP that goes to animal consumption among various communities is as follows.

Tropical rain forest 7

Temperate deciduous for. 5

Grassland 10

Open Ocean 40

Oceanic up welling zones 35

-measured as kilocalories per sq m per year

-clip vegetation at end of season in a m² dry it and weigh it
 
 

Pesticides and Pollution

Pesticides are an integral part of our health and agricultural systems. Pesticides provide many benefits but also cause many problems.

Pest- a species that interferes with human welfare.

ex) weeds, mice, nematodes, bacteria, fungi, bears, wolves (if you are a rancher)

Pesticide- a chemical that kills pests.

Types of pesticides:

Insecticide- Insects

Herbicide- Plants

Fungicide- Fungi

Rodenticide- Rodents

Avicide- Birds

Where are most pesticides used? Agriculture

U.S.- 430,000 metric tons used each year

74% agriculture

13% govt and industry

13% households

1% forests

Are pesticides necessarily bad? No! The problem is that most pesticides have many unintended effects.

Perfect pesticide- narrow spectrum, short-lived, stays put

Most are broad spectrum (especially insecticides)

Longevity depends on the pesticide

It is very difficult to put them exactly where you want them
 
 

First generation pesticides- inorganics and botanicals, natural compounds, not synthetic.

1. inorganic compounds- arsenic, lead, mercury- very toxic and very long lived. Not used much any more, toxic to humans and many other species

2. Botanicals- compounds derived from plant tissues. Easily degraded, don't persist.

ex) pyrethrins- from chrysanthemum flowers- kills insects

ex) rotenone- from roots of derris plant- kills fish

Most plants are in a coevolutionary race with their insect pests. Since plants can't run to escape their predators (herbivores) they combat them with chemicals. These compounds come in two general varieties, digestibility reducing compounds and toxins. DRC's are present in large quantities and make the tissue more difficult for animals to process. Examples are tannins (oaks, redwood) and silica (grasses). Toxins include pyrethrins and rotenone- generally these are derived from protein metabolism and are the compounds that scientists seek for pesticide models. Most of the medicines and many of the pesticides we use today are derived from plant compounds.

Second-generation pesticides- synthetic pesticides produced in the laboratory (structure usually based on botanical compounds).

Kinds of insecticides- based on chemical structure

1. Chlorinated hydrocarbons- organic compound (hydrocarbon) with one or more chlorine molecules attached.

Developed in 1940's

-broad spectrum

-slow to degrade

-lipid soluble

Ex) Clear Lake, CA- applied DDT for mosquito control. Had to increase dosage every year.

-grebes, ospreys, and eagles started having problems reproducing

-entomologists emphatically denied that it could be due to pesticide, they insisted that levels of exposure were much too low to cause problems

-biologists found that birds had DDT levels 1000's of times higher than concentrations in water- what happened? Bioamplification

Bioamplification- increase in concentration of a chemical as it moves through the food chain. Two characteristics that are key: persistence, lipid soluble.

OVERHEAD FIG 22.

ex) DDT concentrations in freshwater lake

Water- 0.00005 ppm

Algae- 0.04 (800 fold increase)

Plant-eating fish- 0.2-1.2 (25 fold increase)

Carnivorous fish- 1-2 ppm (2 fold increase)

Great-blue Heron- 3-76 ppm (1-35 fold increase, 60,000-1.5 million fold incr over water)

Unfortunately despite its ban in the '70's DDT is still with us and still is causing problems. Still used in other countries, still persists in this country (ex) LA Bay and Dave Garcelon's study)

Organophosphates- organic compounds that contain phosphorus. More toxic than OC's but much less persistent and water soluble. Generally act by inhibiting acetylcholinesterase => acetylcholine accumulates, animal goes into spasms and dies. Derived from nerve gas.

ex) Malathion- in many household insecticides. Sprayed on Med Flies.

ex) parathion

ex) diazanon

Carbamates- derived from carbamic acid. Less persistent, water soluble, less toxic than OP's. Also acetylcholinesterase inhibitors.

ex) Carbaryl (Sevin)- in many household insecticides

ex) Propoxur (Baygon)

Herbicides- many different kinds, won't go through them all.

Selective herbicides- kill only certain kinds of plants.

Broadleaf herbicides- kill broadleaf plants- used on cereal crops.

2,4-D, and 2,4,5-T- similar to plant growth hormone.

Herbicide isn't bad but does contain traces of dioxin, which has been shown to cause birth defects and is linked to several types of cancer.

grass herbicides- kill grasses.

Nonselective herbicides- kill all plants.

Benefits of pesticides

Disease control-

ex) Typhus carried by fleas and ticks

ex) malaria- carried by mosquitos (100 million infected)

Sri Lanka reduced incidence of Malaria from 2 million cases to 0 in a few years.

Crop protection-

50% of crops consumed by pests

farmers save $3-5 for every $1 spent

-we set ourselves up for pest outbreaks by planting crops as monocultures.

Other problems with pesticide use-

Genetic resistance- inherited characteristic that decreases the effect of the pesticide on a pest.

-exacerbated by short generation time of insects- quickly develop resistance.

-in 1970 313 insects showed resistence to pesticides

-in 1980 829 " "

OVERHEAD fig 22-5 table 22-2

Ecological imbalances- kills species other than those intended.

ex) predators killed- Predators often have lower growth rates than prey (the pest) and therefore pest population can take off in absence of predator.

OVERHEAD fig 22-6

ex) grasshopper sprays do not reduce indecence of grasshopper outbreaks.

Creation of new pests- pesticides can remove predators/parasites of other potential pests and thereby create new pests.

ex) Red scale on citrus

OVERHEAD FIG 22-7b

Mobility in Environment- often doesn't stay where it is applied.

ex) grasshopper sprays and fish kills

ex) DDT in penguins in Antarctica

ex) enters water table and human water supplies

Effects on human health- see text

Alternatives to pesticides-

Alternative cultivation methods-

rotation- effective against corn root worm

partial harvest- alfalfa

Biological control- naturally occurring pred, parasites, disease to control pests.

ex) Cottony-cushion scale in U.S.- controlled by a beetle

ex) prickly pear in Australia- controlled by a moth

ex) Nosema and grasshoppers

Problems- what if introduced pred/parasite preys on other species?

Genetic control-

Sterile male technique- release 1000's of males that are sterilized by irradiation. Zygotes from such matings will not develop.

Genetically resistant crops-

Has had some successes but pathogens often adapt to disease resistant crops.

Problem- will resistant genes get into pest plants?

Phermones and hormones- see book

Integrated Pest Management- combination of biological, chemical, and other controls. Chemicals are used sparingly and as a last resort.

Requires thorough knowledge of pest life cycle, host cycle, and predators and pathogens of pest.

Pesticide Production

World wide, about 2.5 million tons per year are put into the environment = 5 billion pounds, or nearly 1 pound per person on the planet! In the U.S., compounds are mixed to produce about 50,000 different pesticide products - about 5 lbs per person per year.

Economists view of pollution

Economics- how people use their limited resources to satisfy their unlimited wants.

To an economist, the world is one large marketplace where resources are allocated to a variety of uses and goods and services are consumed and paid for.

Price is determined by supply and demand.

When production or consumption of a product has a harmful side effect, this is known as an external cost. This often is not reflected in the price of the product.

ex) when company makes a prod that results in pollution of a river, price reflects cost of making the product, not the cost of pollution cleanup

ex) harvesting trees and siltation of rivers

*- one of root causes of pollution is the failure to consider external costs in the pricing of goods. Vice president Gore suggests we include a environmental tax on items reflecting the environmental cost of producing the item.

Economists calculate the optimum level of pollution by looking at the marginal cost of pollution (usually in term of human health) and the cost of cleaning it up.

Problems with this approach:

1. difficult to measure monetary cost of pollution

ex) what is the worth of a western meadowlark, a clean river?

2. pollution is a violation of a basic human right

-everyone has the right to a clean environment

3. the effect on the ecosystem is rarely taken into account

-at some point the ecosystem may collapse, we don't know when that may occur but if it does we all are in trouble

Free market approaches to pollution abatement- waste discharge permits or emission reduction credits allow companies to buy and sell the right to pollute.

Government policy and regulations

Historically govt has used a command and control approach

-passage of laws that impose rules that limit amount of pollution that can be released.

ex) catalytic converters

ex) reduction of nitrous oxide emissions by 60% by the year 2003

Legislation- lots of it! see page 124

Clean Air Act- 1963, 1965, 1970, 1977, 1990

Clean Water Act- 1977, 1981, 1987 (up for renewal)

Food, Drug, and Cosmetics Act- 1938, no enforcement provisions

Pesticide chemicals amendment (Miller amendment) set limits on amounts in food

Delaney clause- no substance capable of causing cancer is permitted in processed foods

-has lead to problems, newer safer pesticides have been banned while older, more toxic ones are still being used

Environmental Pesticide Control Act (FEPCA) in 1972, and again in 1975. The main intention of these revisions in the original FIFRA was to change a largely registration-oriented statute to one that was regulatory. The law also changed the administration of the law from the USDA to the Environmental Protection Agency (EPA).

EPA was given the task of:

-reviewing 35,000 pesticides in use when the 1972 amendment was passed,

-establishing tolerances for every pesticide which left residues on food,

-of registering new pesticides.

-In 1972 Congress mandated that EPA complete re-registration of all old pesticides by 1976. By 1978, Congress eliminated the deadline because it was uncertain how long this task of determining the safety of pesticides would take. Instead EPA was required to accomplish the work "as expeditiously as possible." The 1978 amendments also sanctioned a chemical-by-chemical rather than product-by-product approach to the registration process. That is, EPA could assess the approximately 600 basic active pesticide ingredients common to the now 50,000 pesticide products in lieu of evaluating each pesticide individually.

Must be cautious

-we must be careful about thinking things are rosy when they are not

ex) Mobil add

=> everything is fine, environmentalists are extremists

In the add there was the following Quote from G. Easterbrook's book.

[the]"notion of a fragile environment is profoundly wrong. Individual animals, plants, and people are distressingly fragile. The environment that contains them is close to indestructible".

This drips with hypocrisy. Oil companies have been and continue to be one of the biggest opponents of environmental regulations and now they are taking credit for the progress that has been made in cleaning up the environment over the last 30 years.

The problem is everything is not fine, yes we do not have rivers catching on fire, yes pollution levels have been reduced in some cities but habitat is still being consumed at an alarming rate, species are being placed on the endangered species list at a faster rate, not a slower one. Factors affecting human health are getting better in some locations but the main factor affecting the persistence of plant and animal species (habitat loss) is getting worse.

Just looking at aquatic ecosystems it is obvious that everything is not as it should be. For example:

-34% of fish species are rare or endanger of extinction

-65% of crayfish sp. " "

-Out of the 214 Pacific salmon stocks, 74% have a high or moderate risk of extinction

-The hydrological flow has been severely altered in most fresh water bodies outside of Alaska.

This is not to say that things are hopeless but we have a long way to go and must continue to press for a cleaner and healthier environment.
 
 

NUTRIENT CYCLING

There are two things necessary to build an ecosystem

1. Energy- already discussed

2. Nutrients- source of chemicals that form the building blocks of the species that inhabit the area

Energy-which flows in one direction through a system -eventually being lost as unusable heat that is dissipated into space,

Nutrients- retained within the ecosystem cycling from organic to inorganic forms, generally not lost from the biosphere but they may become unavailable to most organisms in some cases.

-only those nutrients near the surface of the earth or dissolved in water are available to living organisms

-these nutrients must be present in particular chemical forms for particular organisms

ex) Carbon in CO₂ is available to plants but not to animals

Carbon must be in the form of sugars (glucose), starches, or fats for animals to use it

-Each element follows a slightly different route in its cycle through the ecosystem

There are four elements that are critical to all living organisms:

Carbon, nitrogen, phosphorus, and water

Nutrient (biogeochemical) cycles- the path of movement of elements through an ecosystem

-nutrients may become unbalanced in some situations leading to changes in the species tat can inhabit an area- this may be due to natural or unnatural causes

ex) Coal and peat- vegetative matter (mostly carbon) that accumulates in sediments and is covered and eventually removed from a system.

ex) intensive cultivation may cause the loss of important nutrients in the soil

-loss of soil organic matter in tropical rain forests

-loss of soil on steep erodible hillsides (India- causes problems in Bangladesh)

ex) removal of tree trunks from forests- large source of carbon is removed and not replenished- how long can this go on?

-most natural systems exist in a steady state in which export of elements is approximately balanced by import. Ecologists are interested in studying global nutrient cycles because human activities are altering these cycles with possible impacts on global climate.

Carbon cycle

-one of the most important cycles

-forms basic building material for many important organic molecules (proteins, carbohydrates)

-small, but very active, reservoir pools that are very vulnerable to human disturbance, which can eventually change weather and climates.

Inorganic forms

Carbon in form of CO₂ makes up 0.03% of atmosphere (gas)

Also dissolved in water as CO₃^-2 (carbonate) or HCO₃^- (bicarbonate)

In rocks (limestone)

Plants convert CO₂ to organic form (glucose) via photosynthesis (also release O₂)

Animals use glucose as fuel for respiration ( and release CO₂)

As organic compounds are used by the plants themselves, some carbon dioxide is returned to the environment, but much is retained in the plant bodies.

Primary consumers obtain heir carbon when they eat plants and higher-level consumers when they use lower-level consumers as food.

Decomposers act on the dead bodies of plants and animals when they die and obtain their carbon from these.

ex) path followed by an individual carbon atom while it is cycling may be quite direct and rapid, depending on how it is used in an organism's body.

-simple sugar molecule you swallow in a glass of juice => absorbed into your bloodstream where it is made available to your cells for cellular respiration and exhaled in the same day

-or could be incorporated into tissues and be part of you for decades after your death

-Similarly, carbon in the wood of a thousand-year old tree will be released only when the wood is digested by fungi and bacteria that release CO₂ as a byproduct of their respiration or if it burns.

Carbon sinks

Large amounts of carbon is removed from the cycle for millions of years in the form shells of marine organisms. Forms limestone, when uplifted this carbon is released back into cycle.

Lots also present in coal and oil deposits.

Global carbon cycle and global warming

When carbon is released from these sinks it can greatly change the global carbon balance.

Carbon dioxide plays an important role in regulating the temperature of the earth. Its molecules permit the passage of short-wave solar radiation through the atmosphere, but the do not let the longer heat waves radiating from the earth's surface to pass back into space. Carbon dioxide thus acts as a type of green hose for the earth (a greenhouse gas, similar to glass panes on an actual greenhouse)

I a relatively short period of time, geologically speaking, the earth has experienced a dramatic influx of carbon in the atmosphere because of human activities. Prior to the large-scale use of fossil fuels and burning of large tracts of forests, these carbon reservoirs did not contribute much to the overall carbon cycle on the planet. They were not generally involved in biological pathways nor did they influence atmospheric carbon dioxide levels. Currently about 7 billion tons of carbon per year are entering the atmosphere from fossil fuel combustion!
 
 

Nitrogen cycle

-nitrogen is one of the most important elements because it forms the building blocks of proteins

-cycling is more complex than for carbon

Inorganic nitrogen

N₂- one of most abundant elements in the atmosphere (78%)

should be readily available to all right? WRONG

-nitrogen is so stable that it does not readily combine with other elements and therefore there is a long process involved in making N₂ available to organisms

It takes a great deal of energy to break apart N₂, there are five steps involved and microorganisms, particularily bg algae are very important

Steps

1. nitrogen fixation

2. nitrification

3. assimilation

4. ammonification

5. denitrification
 
 

1. Nitrogen fixation- N₂=> NH₃ (ammonia)

-mostly completed by cyanobacteria in soils and aquatic environments

-must occur in absence of O₂, where?

-under slime on plant roots

-Rhizobium lives in root nodules of legumes (peas)

-in aquatic enviros, occurs in filamentous cyanobacteria in cells called heterocysts

-takes 12 g of glucose to produce 1 gm of ammonia

2. Nitrification- NH₃ => NO₃^-

-two step process involving Nitrosomonas and Nirrococcus first

-Nitrobactor completes the second step

3. Assimilation- plant roots absorb NO₃^- and incorporate into tissues (proteins)

4. Ammonification- nitrogen waste of living organisms (plants and animals)

-conversion of biological N to ammonia

5. Denitrification- converted back to N₂ by denitrifying bacteria

Human impacts

-humans release a lot of nitrogen into the environment in the form of fertilizers

-in many cases this results in too much of a good thing in aquatic environments

-this causes algal blooms

-when algae dies, depletes O₂ in water

-leads to massive fish kills

-also contamination of ground water with nitrates

Phosphorus cycle- found in DNA

-does not exist in a gaseous state

-cycles from land sediments to oceans and back => slower

Inorgainc P

PO₄^3-- inorganic phosphate

Plants absorb directly and convert to molecules

-lots of phosphorus in bird guano, this transports P from oceans to land (amounts small)
 
 

Human effects

-accelerate loss from land (remove crops or trees and must replenish)

-increase P levels in H₂O when apply fertilizers

-most P comes from mines in Florida
 
 

Hydrological cycle (water)

see text

Classification of vegetation

Vegetative communities form the basis for habitat that is used by wildlife. Plant ecologists have developed a hierarchal approach to describing these communities. These levels from highest down are:

Biosphere- all of the communities of living organisms on earth.

Biome- Large, distinct terrestrial ecosystem characterized by a particular climate, soil, plants, and animals- regardless of where it occurs.

ex) temperate rain forest, tundra

Community- In plant ecology this term has a slightly different meaning than in animal ecology. It refers to repeatable associations of plant species. One or a few dominant species usually define the community.

ex) redwood forest, oak woodland, tall-grass prairie

Association- Like a community but under story vegetation is included in classification.

ex) redwood-oxalis assoc., redwood-sword fern assoc., redwood-rhododendron assoc.

Disturbance

These vegetative communities are not fixed in a particular place but change over time as a result of disturbance and succession.

Types of disturbance

Disturbance is a natural part of all ecosystems. Humans have altered the nature, frequency, and extent of disturbance in ecosystems throughout the world. This has resulted in significant changes in the structure and plant composition of many ecosystems.

Natural disturbance- Disturbances that occur in the absence of human influence. Examples include floods, fire, tree falls, landslides, pest outbreaks

Artificial disturbance- Human induced changes in the nature, frequency, and extent of disturbance. Examples include logging, livestock grazing, fire suppression, road building, dams, etc.

Succession- The sequence of changes in a plant community over time.

Primary succession- Succession starting from bare mineral soil. For example vegetative succession on sand dunes.

Secondary succession- Succession at a formerly vegetated site where the vegetation has been removed or severely altered by natural or artificial disturbance.

Major Ecosystems of the world

We will review the major biomes of the world.

Tundra- open bog like areas of northern most North America

-long harsh winters, very short summers, little precip. (~10-25 cm/yr)

-dominated by low growing perennial flowers, mosses, lichens, grasses, dwarf willows.

-lemmings, snowy owls, arctic foxes, snowshoe hares, shorebirds, musk ox, caribou, no reptiles or amphibians

-young, nutrient poor soils with little organic matter

-permafrost- permanent frozen layer under the ground

-many lakes and streams

-recovers very slowly from disturbance
 
 

Taiga- (boreal forest) 11% or earths land surface

-dominated by spruce, fir, and other conifers, aspen and birch present in some areas (conifers are quite drought tolerant and can survive the long winter when plants cannot absorb water)

-cold severe winters, short growing season (longer than tundra), little precip. (~50 cm/yr) main distinction from tundra is lack of permafrost (or very deep layer)

-soil is acidic and mineral poor

-caribou, wolves, brown or grizzly bear, moose and wolf

-snowshoe hare, lynx, mink, sable (fisher), and many migratory bird species
 
 

Human uses

-mostly pulpwood

Temperate Rain forest- Northwest coast of NA, SE Australia, New Zealand, southern SA

-high annual rainfall (200-500 cm, 80-200 inches) augmented by fog, moderate temperatures

-nutrient poor soils but high organic content

-large evergreen trees dominate, doug fir, west hemlock, coastal redwood (here), Sitka spruce

-rich in epiphytes, mosses, lichen, ferns

-squirrels, deer, many bird species, but relatively depauperate in vertebrate sp. diversity

Human uses

-logging of course!

-has many impacts on the ecosystem, high siltation, change in species composition, change in structure, loss of down-woody debris

Temperate deciduous forest- dominated by deciduous trees -eastern US, Europe and China

-75-125 (30-50 inches) cm/yr precip., hot summers, cold winters

-rich topsoil with clay underneath

-dominant trees in Eastern US include Oaks, hickory, maple, beech, magnolia in the South

-formerly very rich in vertebrate diversity- still rich in birds and amphibians

Human uses

-completely logged over 100 yrs ago (more forest now than 100 yr ago)

-now recovering but many bird species are suffering from fragmentation of the habitat

Temperate grasslands- lower latitudes, transition between forest and desert

-summers are hot, winters cold, rainfall intermediate 25-75 cm (10-30 in.)

-rich organic layer in soil- tends to accumulate

-dominated by various species of grasses, also perennial and annual flowers

-abundant herbivores (Bison, Elk, other ungulates in other regions) now mostly gone

-low bird diversity

Human uses

-agriculture, bread baskets of the world

-one of the most endangered ecosystems

Chaparral- thickets of evergreen shrubs, California, W Australia, around Mediterranean Sea, Chile, South Africa

-mild winters with abundant rainfall, very dry summers

-soil is thin and not very fertile

-fires are frequent

-domin. by dense evergreen shrubs, fire adapted (sprout after fire)

Human uses

-favorable climate => many inhabitants

-problem when combined with high fire danger, suppression only makes the problem worse

Deserts- throughout the world in rainshadows of mountains, concentrated around 30^o latitude N and S

-<25 cm/yr (10 in) generally hot summers, may have cold winters

-plants adapted to dry conditions, reduced leaves or absent, deciduous leaves, spines and thorns for defense, many annual flowers

-animals small, nocturnal, many reptiles
 
 

Savannah (tropical grasslands) grasslands with widely scattered trees, E Africa, S America, N Australia

-Low rainfall 85-150 cm (34-60 in) per yr

-soil low in essential mineral nutrients

-dominated by grasses and occasional trees (acacia)

-fires frequent, many plants fire adapted

-highest diversity of large mammals on the planet

Human uses

-agriculture and grazing

-problems with desertification
 
 
 
 

Tropical rain forests- temperatures and precipitation high

-200-450 cm/yr (80-180 in) much of this recycled from transpiration

-mineral poor soil (leached and nutrients rapidly absorbed) so called "wet deserts"

-2/3 of tropical rain forest has tropical red and yellow soils which are acidic and poor in nutrients. High conc. of iron and AL form insoluble compounds with P, decr. avail of P for plants. Ca and P are leached rapidly. O.1% of nutrients filter deeper than 5 cm into soil

-very productive

] -very diverse in plant species and animal species

-cover 7% of earths surface, contain 50% of species

-on one tree E. O. Wilson found 43 species of ants (= to entire fauna of the British Isles)

-P. Ashton found 700 tree species on 10 1 ha plots in Borneo

-may take hundreds of years to recover after being logged ex) Angkor abandoned in 1431 and the forest still differs from undist tropical rainforest

Human uses

-logging

-agriculture and grazing but doesn't last long
 
 

Tropical dry forests- drier than rain forests

-deciduous trees

-open savannah like conditions

-high plant and animal diversity

Human uses

-agriculture and cattle

-disappearing faster than rainforest
 
 
 
 

Aquatic life zones

salinity and light levels are the most important factors determining aquatic life zones

Freshwater

Rivers and streams- flowing water

Lakes and ponds

Estuaries

Marine

Intertidal-

Benthic- ocean floor

Pelagic- ocean water

Euphotic- 0-100m light penetrates and supports photosynthesis

Neritic province- 0-200 m in depth many organisms- sharks, tuna

Oceanic province- >200 m deep few organisms