t ENVIRONMENTAL SCIENCE€¦ · Example: white-tailed deer and mule deer competing for resources. The competitive exclusion principle states that the niches of organisms can only

ENVIRONMENTAL SCIENCE

Ecology + Biogeochemical Cycles Adv

ance

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Instructor 2014

Ecology

Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All Rights Reserved. Visit us online at www.nms.org

Ecology is the study of the connection between an organism and its environment. The levels studied here will include populations, communities, the ecosystem, and the Biosphere.

• population – a group of one species in a given area that interact and breedproducing viable offspring

• community – all of the biotic (living organisms) factors in a given area• ecosystem – the interaction of a community and its abiotic (non-living)

surroundings• biosphere – life-containing parts of lithosphere (land), hydrosphere (water), and

atmosphere

How organisms fit into their environment and the resources they exploit is referred to as their ecological niche. The ecological niche can be further divided into:

• fundamental niche – the total niche an organism can live in• realized niche – the actual part of the niche an organism occupies due to

competition

Generalist species are those organisms that have a very broad niche. They can easily move from location to location. A raccoon is a good example. Specialists have a very narrow niche and are more susceptible to extinction.

Organisms interact with one another in a variety of ways. Intra-specific competition is competition between members of the same species for resources. Example: white-tailed deer competing over the same forage. Inter-specific competition is when two different species compete for the same resources. Example: white-tailed deer and mule deer competing for resources. The competitive exclusion principle states that the niches of organisms can only overlap for a very brief time. Resource partitioning allows for more niches. This occurs when species use resources in different ways and at different times. An example of this is North American woodpeckers partitioning nesting habitats based on size and age of tree with one species preferring older, larger trees and another species choosing the smaller younger trees. Any abiotic factor that limits the growth of a species or population is known as a limiting factor.

In addition to competition, predator-prey relationships also form in communities. Symbiotic relationships also form between species in a community. These close, intertwined relationships can be defined in three ways.

• mutualism – members of both species benefit, example: flower and bee• commensalism – one species benefits while the other is neither helped nor

harmed. example: cattle egret and cow• parasitism – one species benefits while the other (host) is harmed.

example: tick and jackrabbit

Although all the members of the community have a part in the health of an ecosystem, a few species’ roles are critical to the well-being of that ecosystem. These species, called keystone species, have a greater effect on the ecosystem than their biomass would

Ecology


dictate. Since bees have the ability to pollinate many plants, they are considered keystone species. Indicator species are organisms whose presence helps define an ecosystem. Their health also serves as an early warning system for the overall health of the ecosystem.

Ecosystems are maintained by the one-way flow of energy from the sun to producers (autotrophs) and then to the consumers (heterotrophs). This transfer of energy is illustrated in a variety of ways. Food webs illustrate the flow of energy through the feeding relationships found in an ecosystem (Fig. 1).

Ecological pyramids are also used to illustrate the transfer of energy through feeding levels or trophic levels (Fig. 2). Energy pyramids represent the efficiency of ecosystems. Ten percent of the energy is usually all that is transferred between the levels. Ecological pyramids are also used to illustrate numbers of species and amount of biomass (Fig. 2).

Although all ecosystems change and remain dynamic, they do reach maturity in a fairly predictable manner. This process is called ecological succession. During succession organisms modify their surrounding creating suitable conditions for succeeding organisms. Primary succession is the establishment of a community where one has not existed before (lava flow). This is described as a “soil-less” environment. Pioneer

Fig. 1

Fig. 2

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species (lichens and mosses) are the first inhabitants. Their effects on rock and the decomposition of their biomass help to create soil. Grasses and herbs move in next, further increasing the richness and depth of the soil. And, if precipitation allows, woody plants and trees follow. Secondary succession occurs in areas that have soil. They are generally areas that have been disturbed by natural disasters (forest fire) or habitat destruction by man (abandoned farm land).

Groups of similar ecosystems that occur throughout the planet are classified as biomes. These biomes are generally defined by precipitation, temperature, and the communities they support. Transitions between ecosystems are called ecotones. These ecotones create an edge effect that are generally very biodiverse.

Ecosystems are also maintained by the recycling of matter or nutrients. While energy flows through an ecosystem matter is conserved. Biogeochemical cycles describe the transfer of these nutrients through the living and non-living world. The biogeochemical cycles include:

• Hydrologic Cycle (water cycle)• Nitrogen Cycle• Carbon Cycle• Phosphorus Cycle

Hydrologic Cycle The hydrologic cycle is the movement of water through the biosphere. Many terms such as condensation, evaporation and precipitation are familiar. However, it also includes transpiration (the evaporation of water from the surface of leaves) and infiltration (percolation of water through the soil) (Fig. 3).

Fig. 3

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Nitrogen Cycle Even though nitrogen makes up seventy-eight percent of the atmosphere, it still needs to be converted for organisms to use it. Bacteria are critical in the cycling of nitrogen. Inorganic fertilizers and agricultural runoff are two of the ways man interferes with the nitrogen cycle. Both of these problems can lead to cultural eutrophication of water sources. The steps of the nitrogen cycle follow (Fig. 4):

1. nitrogen fixation – the conversion of atmospheric nitrogen (N2) intoammonia (NH3) or into nitrate (NO3). This is most often done by bacteriafound in the soil. Rhizobium bacteria found in the nodules of legumes areimportant nitrogen-fixing bacteria.

2. nitrification – the conversion of ammonium (NH4) into usable nitrates3. assimilation – plants incorporating the usable forms of nitrogen into

biomass4. ammonification – decomposition of biomass that produces ammonia or

ammonium5. denitrification – denitrifying bacteria converts nitrates into atmospheric

nitrogen

Carbon Cycle Carbon is recycled through the biosphere during photosynthesis and cellular respiration. Plants assimilate carbon dioxide into high energy sugars. When these sugars are consumed by heterotrophs, CO2 is released back into the atmosphere. When both plants and animals die, carbon is trapped until decomposition releases it. Some of these organisms were buried and subjected to heat and pressure before they decomposed and were converted into coal, oil, and natural gas. By burning these fossil fuels, humans are adding CO2 back at a rate that may drastically change our climate. The ocean and many types of rocks also serve as reservoirs for carbon.

Fig. 4

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Phosphorus Cycle The phosphorus cycle is unique in the fact that is does not have an atmospheric component. This makes it a sedimentary cycle. This also makes it the slowest of the biogeochemical cycles. Phosphorus is an important component in many biological compounds, such as nucleic acids. Phosphorus is found in rocks and soils and is released through weathering. When phosphorus is made available for plants to absorb it is called mineralization. While, the immobilization of phosphorus occurs when inorganic phosphorus is converted into organic phosphorus. Much like the nitrogen cycle, microbial activity is involved.

Ecology


(a) Why are zebra mussels located primarily in areas in the eastern United States rather than in the western United States?

One point can be earned for any acceptable explanation:

• The animal was introduced in the eastern U.S. and is still spreading across thecontinent.

• The eastern states have more surface waters available for colonization and to act ascorridors to dispersal; the western states have fewer such habitats.

• The western mountain ranges (e.g., the Rockies) serve as a natural barrier todispersal.

• Humans spread the animal, and human population density is generally higher in theEast.

(b) How are zebra mussels introduced into isolated lakes? Describe one viable method for preventing the spread of zebra mussels into isolated lakes.

Two points can be earned: 1 point for a mechanism by which the mussels are spread and 1 point for a method to prevent mussel introductions. The two responses need not be linked.

Mechanisms of zebra mussel introduction • Transport of boats or boat trailers with mussels attached• Carried in water in boats (excluding ballast, which implies oceangoing vessels)• Inundation of isolated lakes with floodwater containing mussels• Building canals or other waterways between previously isolated lakes• Transport by animal vectors (migratory waterfowl, etc.)• Brought with fish used to stock water bodies

Methods to prevent spread of zebra mussels • Thorough inspection/cleaning of boats before transport or launch• Flushing or draining of water between water bodies• Refraining from building connecting waterways• Education/information campaigns to discourage practices causing spread• Prohibiting transport of boats to unaffected lakes

(c) Identify and explain one impact that zebra mussels can have on aquatic ecosystems.

One point can be earned for naming an impact, and 1 point can be earned for an appropriate explanation. The identification and explanation must be linked.

Impact on Ecosystem / Explanation • Increased water clarity; transparency / Mussels are filter feeders, removing solids

from water as they feed. • Increased light penetration in water column / Remove suspended matter from

water. • Increased photosynthesis/primary productivity / Results from increased water

clarity. • Increased populations of other species (certain fish, waterfowl, etc.) / Results either

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from greater primary productivity (base of trophic pyramid) or greater ability of fish that are visual feeders to see their prey.

• Competition from zebra mussels for available resources / Decreased populations ofother species (mollusks, insects, etc.).

• Decreased populations of other species (mollusks, insects, etc.) / Competition fromzebra mussels for available resources.

• Altered water chemistry / Mussels change biogeochemistry through filtering anddigestion of food; shells sequester; store minerals.

• Disrupts food chains; trophic dynamics / Eats food required by other species.

(d) Identify another invasive species, either terrestrial or aquatic, and describe one negative impact it has had.

One point can be earned for naming a species, and 1 additional point can be earned for an appropriate explanation of its impact. The identification and explanation must be linked. Acceptable examples include:

Invasive Species / Negative Impact • Cane toad / Toxin kills native predators.• Rats / Eat bird’s eggs; spread disease.• Purple loosestrife / Crowds out native plant species in wetlands.• (Eurasian) water milfoil / Crowds out native plants, clogs waterways.• Snakehead fish / Preys on native fish, reducing populations.• Rabbits / Clear vegetation.• Kudzu vine / Smothers other vegetation.• Emerald ash borer / Burrowing and feeding kill trees.• Sea lamprey / Predation harms other fish.• Nutria / Eats marsh vegetation, destroying wetlands.• (Brazilian) pepper tree / Tissues are toxic; shades out other plants.• Pythons, constrictors / Eat native species, lowering populations.• Japanese/Asian beetles / Eat native plant species.• Pigeon/rock dove / Nuisance in cities; vectors of disease.• (European) starlings / Compete with native birds for nest sites.• Feral domestic animals (e.g., boar, cat) / Predators of native species.• Ice plant / Competes with native plant species.• Africanized (“killer”) bees / Attacks people/animals; displaceshoneybees.• Boll weevil / Important crop pest.

Note: A correct response must identify a specific organism. General categories of biota (e.g., “snakes”) are not acceptable.

(e) One strategy for controlling an invasive species has been to introduce another nonnative species to control it; this strategy can often have unintended results. Give a specific example of the use of this strategy and discuss a negative impact of introducing a nonnative species to control an invasive species.

One point can be earned for identifying a specific example of biological control, and 1 additional point can be earned for an appropriate explanation of a potential negative impact. The two responses need not be linked.

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Acceptable examples include:

Biological Control • Insects (stem borers, leaf eaters) to feed on purple loosestrife• Ladybird beetles (ladybugs) to feed on pest insects• Parasitoid wasps to control weevils• Bacteria (e.g., Bt) or viruses to control animal pests• Mongoose to hunt rats• Cane toads to prey on insect pests

Negative Impact • Predation of nontarget species• Competition with native species• Toxic to native predators, or reduces available food to native predators• Alters ecological interactions, e.g., food webs or biogeochemical cycles

Note: The “specific example” cannot be hypothetical or a general prescription, e.g., “introduce a predator of agricultural pests.”

(f) Discuss TWO specific characteristics of invasive species that enable them to thrive in new environments.

Two points can be awarded: 1 point for each specific characteristic.

• Generalist species• Excellent dispersal mechanisms, allowing it to spread• R-selected or r-strategist

OR any of the following characteristics: o Large clutch size/many offspring producedo Early onset of reproduction/early maturationo Frequent reproduction

• Superior defenses against predators in new environment• Superior skills as a predator in new environment

Note: Listed characteristics must be specific. Generic qualities or life-history strategies are not acceptable.

t ENVIRONMENTAL SCIENCE€¦ · Example: white-tailed deer and mule deer competing for resources. The competitive exclusion principle states that the niches of organisms can only

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