Ecosystems: What are They?
Unit 1 Chapter 2
Important Vocabulary
y Biotic Communities – are all the plants and animals, both large and very small, that inhabit a natural community. y The type of biotic community found in a particular area is determined by the abiotic
factors – non‐living factors (water, climate, type of soil, etc.)
y Abiotic factors determine and limit the type of life in a particular area. Important Vocabulary
• Species – members of a population that can interbreed and produce fertile offspring. • Population – a particular number of individuals that make up a species in a given area. • Communities – All the populations that live and interact in a particular area. • Ecosystem – A dynamic complex of plant, animal, & microorganism communities and the non‐living environment interacting as a functional unit in a particular area. • Landscape – a group of interacting ecosystems in a particular area. Important Vocabulary
• Ectone – species do not stay in one ecosystem. Rather, they may move between 2 or more closely associated ecosystems. • Biosphere – All species and physical factors on Earth functioning as one unified system. Interactions
• It is important to remember that nothing lives in a bubble. Everything is influenced by everything else:
• Non‐living factors influence the living.
• Species interact and influence each other. • Populations influence other populations. • Communities influence each other, as do ecosystems. • If we neglect to take this into consideration, we stand to do serious damage to established systems. Structure of Ecosystems
• It is imperative that we understand how the biotic and abiotic factors fit and work together in an ecosystem. • Any changes we may make to an ecosystem may have many unknown, unforeseen, unintended consequences. • Sometimes we think that we are helping the environment, when in reality, we may very well be causing serious damage. Trophic Structure
• Every living organism in an ecosystem has an ecological niche, which is, what the organism feeds on, where it feeds, when it feeds, how it responds to abiotic factors, & where it lives and nests. • An organism will fit into 1 of 2 categories in terms of food:
1) Autotrophs – organisms that make their own food (plants).
2) Heterotrophs – organisms that must get their food from an outside source. Producers
• Producers are autotrophs. • They are the plants that use the sun, water, CO2, & minerals in order to produce complex organic materials. • Organic compounds contain carbon and are the products of living things (sugars, carbohydrates, even oil, wood, & coal, etc.)
• Other compounds/materials that exist apart from living things are considered inorganic
(water, CO2, minerals, etc.)
Consumers
• Consumers form the next level and are heterotrophs. • Consumers range from microscopic bacteria & protists all the way up to humans. • Consumers are divided into subgroups based on what they eat:
– Primary consumers – are herbivores & consume solely producers. They range from small mites up to cows and elephants. – Secondary consumers: – Carnivores – Animals that feed solely on primary consumers.
– Omnivores– Consumers that feed on both plants and animals.
• Animals can occupy more than 1 place on the food chain (humans, bears, etc.)
• In any relationship where 1 organism feeds on another, one is the predator Æ the one that does the feeding, and the other is the prey Æ
the one that is fed upon. Consumers
Parasites
• Parasites are also another very important category of consumers.
• Parasites are organisms that become very closely associated with their prey, and feed upon it over a period of time, usually without killing it. • The organism that is being fed upon is called the host. • Parasite can be insects, worms, fungi (athlete’s foot), plants, and even mammals (vampire bats and sea lamprey). • Although we usually refer to disease causing bacteria and viruses as pathogens, they are really specialized parasites. Consumers
Detritus Feeders and Decomposers
• The 3rd big category of consumers consists of detritus feeders and decomposers. • Q: What is detritus?
• It is dead plant material such as leaves, branches, trunks, etc., animal wastes, & dead animals.
• Organisms that are specialized to feed on detritus are called detritivores (earthworms, termites, ants fiddler crabs, etc.)
Consumers
• Decomposers are an extremely important category of detritivores (fungi and bacteria). • Detritus appears to rot away. This is the metabolic activity of fungi and bacteria as they consume the detritus. • Q: Decomposers are incredibly important to the proper functioning of the natural world. Why?
• It is important that detritus gets broken down in order to recycle nutrients back into the ecosystem. • When a plant dies, it is fed upon by decomposers. When a decomposer dies, they are fed upon by secondary detritus feeders, and so on, thereby creating a source of energy and nourishment for other organisms further up the food chain. Trophic Structure of Ecosystems
• Despite the diversity of ecosystems, they all have a similar biotic structure. All consist of:
– 1) Autotrophs/Producers – which produce the orgaic
matter. – 2) Heterotrophs – which consist of a variety of categories of consumers. Trophic Relationships
Food Chain
• A food chain shows a possible transfer of energy between producers and consumers. • Example: Mouse eats a nut, cat eats the mouse, we eat General Tso’s “chicken.” • Alternative Example: Caterpillar eats an oak leaf, warbler eats the caterpillar, hawk eats the warbler. Trophic Relationships • Although this is a probable pathway demonstrating the transfer of energy, it is important to understand that food chains, such as this, rarely exist as isolated entities. • Caterpillars eat several types of leaves, are preyed upon by several types of birds, etc.
Trophic Relationships
Food Web
• A food web is a complex, interconnected series of food chains. • Food webs all consist of a series of levels ranging from producers to secondary consumers. • These levels, are called trophic levels. • All producers belong to the first trophic level, all primary consumers (herbivores) to the second level, secondary consumers to the third level, and so on. Food Webs
Trophic Relationships
Trophic Levels
• Trophic levels demonstrate the flow of energy. • How many trophic levels are there?
• Usually there are no more than 3 or 4 in terrestrial ecosystems, and sometimes 5 in marine ecosystems. • Why is this?
• You need enough food for all organisms at all levels. • If we collect all biomass from each trophic level, we can mathematically calculate how many trophic levels can be supported for a given area. Trophic Relationships
• In terrestrial systems, the biomass usually decreases by about 90% as your move up through each level. • Example: » Biomass of producers = 2000 lbs per acre
» Biomass of herbivores = 200 lbs per acre
» Biomass of carnivores = 20 lbs per acre
• At this rate, you can’t go through too many trophic levels before the biomass = 0.
Non‐feeding Relationships
• Ecosystems are characterized by feeding structures, and although you many think that one species will benefit and the other will be harmed, this is not always the case. • Symbiotic Relationships – are those that involve close interactions between 2 organisms. They may be beneficial or harmful in nature. Non‐feeding Relationships
Types of Symbiotic Relationships:
• Many relationships provide a mutual benefit to each organism, and is referred to as mutualism. • Example: Insects benefit by consuming nectar from plants, and plants benefit by having their pollen distributed. Non‐feeding Relationships •
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Some organisms have an incredibly close relationship, even to the point that one cannot live without the other.
Example: Lichens are composed of 2 organisms, fungi and algae.
The fungus provides the alga with a place to live, and the alga provides the fungus with food. Non‐feeding Relationships •
Some symbiotic relationships are harmful to one organisms, and these are referred to as parasitic.
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Yet other relationships are commensal, that is, one organism benefits, while the other is neither harmed nor helped (Hermit crabs use shells built by other organisms). Competitive Relationships • Interestingly, competition rarely exists between species in nature. • Species that live in a particular habitat (the type of place defined by the plant community and physical enviornment), occupy very specialized ecological niches (what the animal feeds on, where it feeds, when it feeds, where it finds shelter, how it responds to abiotic factors, and where it nests). • Competitions is minimized because the different species use different resources. • Example: Bats and some birds both feed on insects, but birds do so during the day, and bats do so at night. Competitive Relationships • Some species, will utilize different portions of a shared space, thereby eliminating competition. This is know as resource partitioning. • Sometimes, there is inevitable overlap between species’ niches.
• When this occurs, one species may eliminate another through competition. i.e. Think of weeds in a flower bed. • When 2 species compete directly for a resource, as may be the case with a foreign, introduced species and a native species, 1 of the 2 species will generally lose out. This is known as the competitive exclusion principle. Abiotic Factors
• Abiotic Factors can be broken into:
• Conditions – factors that vary in space and time
but are not used up or made unavailable to other
species
– Ex. Wind, pH, temperature, salinity, rocks, etc.
• Resources – any factors (abiotic or biotic) that are
used up/consumed by organisms.
– Ex. Water, nutrients, light, space, etc.
Abiotic Factors:
Optimum, Zones of Stress, and Tolerance
• For every factor, organisms have a certain level at which they do best, know as their optimum or optimum range. • Beyond this optimum range there is a range that organisms will tolerate Æ range of tolerance. • At the end points of this range, are the limits of tolerance, beyond which death occurs. • As you move away from the optimum range and toward each limit of tolerance stress increases Æ
zones of stress. Law of Limiting Factors
• A limiting factor is anything that limits growth. • Any factor that exists outside an organism’s optimal range will cause stress and therefore limit growth. • Several factors may combine to severely limit growth or kill an organism. • The concept of optimums and limiting factors determine biotic communities, thereby creating a variety of ecosystems, landscapes, and biomes. Ecosystems and Biomes
The Role of Climate:
• Climate is a description of the average temperature and precipitation that is expected for a given area. • A given climate will support only those species whose temperature and precipitation optimums fall into that particular range. Limiting Factors: Microclimates
• Microclimates occur when a specific site may have conditions that are significantly different from the overall climate of the area. • Ex. South facing slopes are sunnier, and therefore warmer; land directly adjacent to a river may be a flood plain, and will therefore be continuously wet; etc. • Human Created Microclimates: a specific site has dramatically different conditions due to human influence. • Ex. Heat Island Effect: large cities with a lot of pavement and glass are often significantly warmer that the surrounding landscape. Limiting Factors: Abiotic Factors and Physical Barriers
• Abiotic factors other than temperature and rainfall may also limit the type of life that can occupy a particular area. • Some of there factors include sunlight, salinity, soil type, etc.
• Yet other factors that limit the species to a particular area include physical barriers.
• Some physical barriers are natural, such as mountain ranges, and large bodies of water, while others are man‐made, such as dams, cities, highways, etc.