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Transcript
Ecology Topic 5.1, 5.2, 5.3 Option G1, G2, G3, G4, and G5 Ecology Ecology is the study of how organisms interact with their environment and each other. • This interaction of organisms is a two-way interaction. Organisms are affected by their environment, but by their activities they also change the environment. Levels of Organization • Ecology is studied on several levels: – Organism • Ecologists may examine how one kind of organism meets the challenges of its environment, either through its physiology or behavior. – Population • Group of individuals of the same species living in a particular geographic area. – Community • Consists of all the populations of different species that inhabit a particular area. – Ecosystem • Includes all forms of life in a certain area and all the nonliving factors as well. – Biosphere • The global ecosystem; the sum of all the planet’s ecosystems. • Most complex level in ecology, including the atmosphere to an altitude of several kilometers, the land down to and including water-bearing rocks under 3,000 m under Earth’s surface, lakes and streams, caves, and the oceans to a depth of several kilometers. • It is self contained, or closed, except that its photosynthesizers derive energy from sunlight, and it loses heat to space. Levels of Organization Abiotic vs. Biotic Abiotic components Temperature, forms of energy, water, inorganic nutrients, and other chemicals. Biotic components Organisms making up the community Habitat Habitat The specific environment in which an organism lives in. Each habitat can be described by characteristic abiotic factors. Abiotic Factors Physical and chemical factors (abiotic) affecting the organisms living in a particular ecosystem: Solar energy Water Temperature Wind Soil composition Unpredictable disturbances Abiotic Factors- Solar Energy Powers nearly all terrestrial and shallow-water ecosystems. In aquatic environments that sunlight reaches, the availability of light has a significant effect on the growth and distribution of photosynthetic bacteria and algae. Most photosynthesis occurs near the surface of a body of water. In terrestrial environments, light is often not the most important factor limiting plant growth. In many forests, however, shading by trees creates intense competition for light at ground level. Abiotic Factors- Water Essential to all life. Aquatic organisms have a seemingly unlimited supply of water, but they face problems of water balance if their own solute concentrations does not match that of their surroundings. These organisms confront solute conc. in freshwater lakes and streams that are very different from those in the sea. For a terrestrial organism, the main water problem is the threat of drying out. Many land species have watertight coverings that reduce water loss. Most terrestrial animals have kidneys that save water by excreting very concentrated urine. Abiotic Factors- Temperature An important abiotic factor because of its effect on metabolism. Few organisms can maintain a sufficient active metabolism at temperatures close to 0 degrees Celsius, and temperatures above 45 degrees Celsius destroy the enzymes of most organisms. Extraordinary adaptations enable some species to live outside this temperature range. For example, some of the frogs and turtles living the northern United States and Canada can freeze during winter months and still survive, and bacteria living in hydrothermal vents and hot springs have enzymes that function optimally at extremely high temperatures. Mammals and birds can remain considerably warmer than their surroundings and can be active in a fairly wide range of temperatures, but even these animals function best at certain temperatures. Abiotic Factors- Wind An important abiotic factor for several reasons. Local wind damage often creates openings in forests, contributing to patchiness in ecosystems. Wind also increases an organism’s rate of water loss by evaporation. The resulting increase in evaporative cooling can be advantageous on a hot summer day, but it can cause dangerous wind chill in the winter. Abiotic Factors- Soil composition Most soils are complex combinations of inorganic nutrients, organic materials in various stages of decomposition, water, and air. Such variables as soil structures, pH, and nutrient content often play major roles in determining the distribution of organisms. Abiotic Factors- Unpredicatable disturbances Include fires, hurricanes, tornadoes, tsunamis, and volcanic eruptions. Fire occurs frequently enough in some communities, however, that many plants have adapted to this periodic disturbance. Natural Selection and Abiotic Factors Organisms are adapted to abiotic and biotic factors by natural selection. An organism’s ability to survive and reproduce in a particular environment is a result of natural selection. By eliminating the least fit individuals in populations, environmental forces help adapt species to the mix of abiotic and biotic factors that they encounter. The presence of a species in a particular place can come about it two ways: The species may evolve in that location. The species may disperse to that location and be able to survive. Biomes Biomes- A large ecosystem that is usually determined by climate and categorized by the available producers and other organisms that adapted to the particular environment. The major terrestrial biomes are named after the climatic conditions and the vegetation, however, their microbial organisms, fungi, and animals are also important. Climatograms Used to compare the annual precipitation and annual temperature in various biomes. Biomes Biomes- Tropical Rainforest Temperature is warm all year long and has about 11-12 hours of sunlight. Plenty of rain (200-400 cm per year) results in fast decomposition, as a result the soil is very thin. Very complex species diversity Vegetation includes trees, vines, and epiphytes. Very rich animal diversity. Biomes- Shrublands (savanna, chaparral) Lower rainfall (30-50 cm a year) and warm temperatures year round. The plants are fire adapted because of the frequent fires. Typical plants are grasses with scattered trees and shrubs. Grazing animals, insects, birds, large predators. Biomes- Deserts Very dry areas with less than 2 cm of yearly rainfall, very large temperature fluctuations. They can grow some deep rooted shrubs, cacti, and other succulent plants, annual plants with very fast growing period Adaptations to extreme dry conditions. Biomes- Temperate Deciduous Forests Warm summers, cold winters. Fairly even annual rainfall (60-150 cm) Dominant species are various broad leaf trees, such as oak, maple, hickory, birch, etch. Various shrubs and annuals are found in the broad leaf regions. Biomes- Taiga Long, cold winters and short, wet summers that are sometimes warm. Soil is acidic and nutrient-poor, not fit for many plants. Biomes- Tundra Bitter cold winters, high winds and low precipitation (15-25 cm). Because the soil is constantly frozen, the temperatures are low and the evaporation is also low, the soil is constantly saturated with water. Vegetation includes dwarf shrubs, grasses, mosses, and lichens. Characterized by permafrost, continuously frozen subsoil. Community A biological community is an assemblage of all the populations of organisms living close enough together for potential interaction. Key characteristics of a community: 1.Species diversity 2.Dominant species 3.Response to disturbances 4.Trophic structure 5. Community interactions Community 1.Species diversity The variety of different kinds of organisms that make it up, Has two components: 1. species richness The total number of different species in the community. The more species present in a sample, the 'richer' the sample. Species richness as a measure on its own takes no account of the number of individuals of each species present. It gives as much weight to those species which have very few individuals as to those which have many individuals. Thus, one daisy has as much influence on the richness of an area as 1000 buttercups. 2. species abundance (sometimes referred to as “evenness”) a measure of the relative abundance of the different species making up the richness of an area. To give an example, we might have sampled two different fields for wildflowers. The sample from the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from the second field comprises 20 daisies, 49 dandelions and 931 buttercups (see the table below). Both samples have the same richness (3 species) and the same total number of individuals (1000). However, the first sample has more evenness than the second. This is because the total number of individuals in the sample is quite evenly distributed between the three species. In the second sample, most of the individuals are buttercups, with only a few daisies and dandelions present. Sample 2 is therefore considered to be less diverse than sample 1. Community 1.Species diversity (continued) A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance. As species richness and evenness increase, so diversity increases. Simpson's Diversity Index is a measure of diversity which takes into account both richness and evenness. n = the total number of organisms of a particular species N = the total number of organisms of all species The value of D ranges between 0 and 1. With this index, 1 represents infinite diversity and 0, no diversity. http://geographyfieldwork.com/Simpson'sDiversityIndex.htm Community 2.Dominant species In general, a small number of species exert strong control over a community’s composition and diversity. In terrestrial situations, the dominant species is usually the most prevalent form of vegetation. For example, wildflowers are the dominant species in some communities. The types and structural features of plants largely determine the kinds of animals that live in a community. Keystone species is a species that exerts strong control on community structure because of its ecological role, or niche. For example, a seastar of the genus Pisaster is a keystone predator that reduces the density of the strongest competitors in the community, thus preventing the competitive exclusion of weaker competitors. In an experiment on the Washington coast, Pisaster was removed from the community. The results was that the Pisaster’s main prey, a mussel of the genus Mytillus, outcompeted many of the other shoreline organisms reducing the number of organisms from over 15 species to under 5 species. Community Community 2.Dominant species (continued…) Keystone species (continued…) Also, sea otters are a keystone predator in the North Pacific. Sea otters feed on sea urchins, and sea urchins feed mainly on kelp, a large seaweed. In areas where sea otters are abundant, sea urchins are rare and kelp forests are well developed. Where sea otters are rare, sea urchins are common and kelp is almost absent. During the last 20 years, sea otters have declined dramatically in large areas off the coast of western Alaska. The loss of this keystone species has allowed sea urchin populations to increase, resulting in the destruction of kelp forests. Killer whales are the cause of the sea otter decline, which is probably because the previous prey of the whales, mainly seals and sea lions, have declined in density. The decline of these prey species reflects a decline in the populations of fish species that the seals and sea lions eat. And, all of these changes in the Alaskan marine communities are probably related to human overfishing in the North Pacific Community Community 3. Response to Disturbances Events such as storms, fire, floods, droughts, overgrazing, or human activity that damage biological communities, remove organisms from them, and alter the availability of resources. The types of disturbances and their frequency and severity vary from community to community. Small-scale disturbance often have positive effects. For example, when a large tree falls in a windstorm, it disturbs the immediate surroundings, but it also creates new habitats. For instance, more light may now reach the forest floor, giving small seedlings the opportunity to grow; or the depression left by its roots may fill with water and be used as egg-laying sites by frogs, salamanders, and numerous insects. Small-scale disturbances may enhance environmental patchiness, which can contribute to species diversity in a community. Communities change drastically following a severe disturbance that strips away vegetation and even soil. The disturbed area may be colonized by a variety of species, which are gradually replaced by a succession of other species, in a process called ecological succession. Community 3. Response to Disturbance (continued)… Early successional communities are characterized by a low species diversity, simple structure and broad niches The succession proceeds in stages until the formation of a climax community. The most stable community in the given environment until some disturbance occurs. Two types of Ecological Succesion: Primary Succession Secondary Succession Community 3. Response to Disturbances (continued…) Primary succession When ecological succession begins in a virtually lifeless area with no soil. Usually takes hundreds or thousands of years. For example, new volcanic islands or rubble left by a retreating glacier. Often the only life-forms initially present are autotrophic bacteria. Lichens and mosses are commonly the first large photosynthesizers to colonize the area. Soil develops gradually as rocks weather and organic matter accumulates from the decomposed remains of the early colonizers. Lichens and mosses are gradually overgrown by grasses and shrubs that sprout from seeds blow in from nearby areas or carried in by animals. Eventually, the area is colonized by plants that become the community’s prevalent form of vegetations. Secondary succession Occurs when a disturbance has destroyed an existing community but left the soil intact. For example, forested areas that are cleared for farming, areas impacted by fire or floods. Community 3. Response to Disturbances (continued…) Primary Succession Example: autotrophic prokaryoteslichens, mossesgrassesshrubstreesclimax communty Secondary Succession Example: herbaceous plants woody shrubs trees climax community Community 4. Trophic structure The feeding relationships among the various species making up the community. A community’s trophic structure determines the passage of energy and nutrients from plants and other photosynthetic organisms to herbivores and then to carnivores. The sequence of food transfer up the trophic levels is known as a food chain Trophic levels are arranged vertically, and the names of the levels appear in colored boxes. The arrows connecting the organisms point from the food to consumer. This transfer of food moves chemical nutrients and energy from the producers up though the trophic levels in a community. Community 4. Trophic Structure (continued…) At the bottom, the trophic level that supports all others consists of autotrophs, called producers. Photosynthetic producers use light energy to power the synthesis of organic compounds. Plants are the main producers on land. In water, the producers are mainly photosynthetic protists and cyanobacteria, collectively called phytoplankton. Multicellular algae and aquatic plants are also important producers in shallow waters. All organisms in trophic levels about the producers are heterotrophs, or consumers, and all consumers are directly or indirectly dependent on the output of producers. Community 4.Trophic Structure (continued…) Trophic Levels: Primary producers Mostly photosynthetic plants or algae Primary consumers Herbivores, which eat plants, algae, or phytoplankton. On land include grasshoppers and many insects, snails, and certain vertebrates like grazing mammals and birds that eat seeds and fruits aquatic environments include a variety of zooplankton (mainly protists and microscopic animals such as small shrimp) that eat phytoplankton. Secondary consumers Include many small mammals, such as a mouse, a great variety of small birds, frogs, and spiders, as well as lions and other large carnivores that eat grazers. In aquatic ecosystems, mainly small fishes that eat zooplankton Tertiary consumers Snakes that eat mice and other secondary consumers. Quaternary consumers Include hawks in terrestrial environments and killer whales in marine environment. Community 4.Trophic Structure (continued…) Another trophic level of consumers are called detrivores which derive their energy from detritus, the dead material produced at all the trophic levels. Detritus includes animal wastes, plant litter, and all sorts of dead organisms. Most organic matter eventually becomes detritus and is consumed by detritivores. A great variety of animals, often called scavengers, eat detritus. For instance, earthworms, many rodents, and insects eat fallen leaves and other detritus. Other scavengers include crayfish, catfish, crows, and vultures. A community’s main detritivores are the prokaryotes and fungi, also called decomposers, or saprotrophs, which secrete enzymes that digest organic material and then absorb the breakdown products. Enormous numbers of microscopic fungi and prokaryotes in the soil and in mud at the bottom of lakes and oceans convert (recycle) most of the community’s organic materials to inorganic compounds that plants or phytoplankton can use. The breakdown of organic materials to inorganic ones is called decomposition. Community Community 4.Trophic Structure (continued…) A more realistic view of the trophic structure of a community is a food web, a network of interconnecting food chains. Food webs, like food chains, do not typically show detrivores, which consume dead organic material from all trophic levels. Community 5. Community Interactions Interspecific competition: If two different species are competing for the same resource. Causes the growth of one or both populations may be inhibited. May play a major role in structuring a community. Weeds growing in a garden compete with garden plants for nutrients and water. Lynx and foxes compete for prey such as snowshoe hares in northern forests. Community 5. Community Interactions (continued…) Competitive exclusion principle In 1934, Russian ecologist Gause studied the effects of interspecific competition in laboratory experiments with two closely related species of Paramecium. Gause cultured these protists under stable conditions with a constant amount of food added every day. When he grew the two species in separate cultures, each population grew rapidly and then leveled off at what was apparently carrying capacity of the culture. But when Gause cultured the two species together, one species was driven to extinction. Gause concluded that two species so similar that they compete the same limited resources cannot coexist in the same place. One will use the resources more efficiently and thus reproduce more rapidly than the other. Even a slight reproductive advantage will eventually lead to local elimination of the inferior competitor. Community 5. Community Interactions (continued…) The competitive exclusion principle applies to what is called a species’ niche. In ecology, a niche is a species’ role in its community, or the sum total of its use of the biotic and abiotic resources of its habitat. For example, the attachment sites on intertidal rocks, the amount of exposure to seawater and air, and the food it consumes are some of the aspects of each barnacle’s niche. The fundamental niche of a species includes the total range of environmental conditions that are suitable for existence without the influence of interspecific competition or predation from other species. The realized niche of a species is the actual mode of existence, which results from its adaptations and competition with other species. Combining the niche concept with the competitive exclusion principle, we might predict that two species cannot coexist in a community if their niches are identical. Figure 9g-1: The following diagram shows a hypothetical situation where a species distribution is controlled by just two environmental variables: temperature and moisture. The green and yellow areas describe the combinations of temperature and moisture that the species requires for survival and reproduction in its habitat. This resource space is known as the fundamental niche. The green area describes the actual combinations of these two variables that the species utilizes in its habitat. This subset of the fundamental niche is known as the realized niche. Community 5. Community Interactions (continued…) There are two possible outcomes of competition between species having identical niches: Either the less competitive species will be driven to local extinction, or one of the species may evolve enough through natural selection to use a different set of resources. This differentiation of niches that enables similar species to coexist in a community is called resource partioning. It is a way in which different species can use the same resource, such as food, without occupying the same physical location at the same point in time. For example, different warblers eat the same caterpillar, but they occupy different positions in the tree. Two primarily occupy the area near the trunk, with the others share the edges of the branches, but at different heights. The result is the warblers do not overtly compete for food in the same space. Community 5. Community Interactions (continued…) Predation is an interaction between species in which one species, the predator, kills and eats another, the prey. Because eating and avoiding being eaten are prerequisites to reproductive success, the adaptations of both predators and prey tend to be refined through natural selection. Examples of prey capturing strategies: Most predators have acute senses enable them to locate prey. In addition, adaptations such as claws, teeth, fangs, stingers, or poisons help catch and subdue prey. Predators are generally fast and agile, whereas those that lie in ambush are often camouflaged in their environments. Predators may also use mimicry; some snapping turtles have a tongue that resembles a wriggling worm, thus luring small fish. Community Camouflage Chemical Defense Community 5. Community Interactions (continued…) Predator defenses: Mechanical defenses: such as the porcupine’s sharp quills or the hard shells of clams and oysters. Chemical defenses: animals are often bright colored, a warning to predators; like a poison arrow-frog or a skunk. Batesian mimicry: a palatable or harmless species mimics an unpalatable or harmful one; like the king snake mimics the poisonous coral snake Mullerian mimicry: two unpalatable species that inhabit the same community mimic each other; like bees and wasps Mullerian Mimicry Batesian Mimicry Community 5. Community Interactions (continued…) Herbivory Animals that eat plants or algae Aquatic herbivores include sea urchins, snails, and some fishes. Terrestrial herbivores include cattle, sheep, and deer, and small insects. Herbivorous insects may locate food by using chemical sensors on their feet, and their mouthparts are adapted for shredding tough vegetation or sucking plant juices. Herbivorous vertebrates may have specialized teeth or digestive systems adapted for processing vegetation. They may also use their sense of smell to identify food plants. Because plants cannot run away from herbivores, chemical toxins, often in combination with various kinds of anti-predator spines and thorns, are their main weapons against being eaten. Community 5. Community Interactions (continued…) Herbivory Some herbivore-plant interactions illustrate the concept of coevolution, a series of reciprocal evolutionary adaptations in two species. Coevolution occurs when a change in one species acts as a new selective force on another species, and counteradaptation of the second species in turn affects the selection of individuals in the first species. For example: an herbivorous insect (the caterpillar of the butterfly Heliconius, top left) and a plant (the passionflower Passiflora, a tropical vine). Passiflora produces toxic chemicals that protect its leaves from most insects, but Heliconius caterpillars have digestive enzymes that break down the toxins. As a result, Heliconius gains access to a food source that few other insects can eat. o The Passiflora plants have evolved defenses against the Heliconius insect. The leaves of the plant produce yellow sugar deposits that look like Heliconius eggs. Therefore, female butterflies avoid laying their eggs on the leaves to ensure that only a few caterpillars will hatch and feed on any one leaf. Because of this, the Passiflora species with the yellow deposits are less likely to be eaten. Community Passiflora Community 5. Community Interactions (continued…) Symbiotic Relationships are interactions between two or more species that live together in direct contact. Three main types: Parasitism Commensalism Mutualism *Parasitism and mutualism can be key factors in community structure. Community 5. Community Interactions (continued…) Parasitism A parasite lives on or in its host and obtains its nourishment from the host. For example: A tapeworm is an internal parasite that lives inside the intestines of a larger animal and absorbs nutrients from its hosts. Another example: Ticks, which suck blood from animals, and aphids, which tap into the sap of plants, are examples of external parasites. Natural selection favors the parasites that are best able to find and feed on hosts. Natural selection also favors the evolution of host defenses. For example, the immune system of vertebrates provides a multiprolonged defense against specific internal parasites. With natural selection working on both host and parasite, the eventual outcome is often a relatively stable relationship in which the host is not usually killed. Tapeworm in small intestine Tick on dog Community 5. Community Interactions (continued…) Commensalism One partner benefits without significantly affecting the other. Few cases of absolute commensalism have been documented, because it is unlikely that one partner will be completely unaffected. For example: algae that grow on the shells of sea turtles, barnacles that attach to whales, and birds that feed on insects flushed out of the grass by grazing cattle. Algae on Sea Turtle Barnacles on Whale Community 5. Community Interactions (continued…) Mutualism Benefits both partners in the relationship. For example: the association of legume plants and nitrogen-fixing bacteria. Bacteria turn nitrogen in the air to nitrates that the plants can use Another example: Acacia trees and the predaceous ants they attract. Tree provides room and board for ants Ants benefit the tree by attacking virtually anything that touches it. Acacia Trees and Ants Ecosystems An ecosystem consists of all the organisms in a community as well as the abiotic environment with which the organisms interact. Ecosystems can range from a microcosm such as a terrarium to a large area such as a forest. Regardless of an ecosystem’s size, its dynamics involve two processes- energy flow and chemical cycling. Energy flow: the passage of energy through the components of the ecosystem. For most ecosystems, the sun is the energy source, but exceptions include several unusual kinds of ecosystems powered by chemical energy obtained from inorganic compounds. For example, an a terrarium, energy enters in the form of sunlight. Plants (producers) convert the light energy to chemical energy. Animals (consumers) take in some of this chemical energy in the form of organic compounds when they eat the plants. Detrivores, such as bacteria and fungi in the soil, obtain chemical energy when they decompose the dead remains of plants and animals. Every use of chemical energy by organisms involves a loss of some energy to the surroundings in the form of heat. Eventually, therefore, the ecosystem would run out of energy if it were not powered by a continuous inflow of energy from an outside source. Ecosystems Ecosystems Chemical cycling: involves the transfer of materials within the ecosystem. An ecosystem is more or less self-contained in terms of matter. Chemical elements such as carbon and nitrogen are cycled between abiotic components (air, water, and soil) and biotic components of the ecosystem. The plants acquire these elements in inorganic form from the air and soil and fix them into organic molecules, some of which animals consume. Detrivores return most of the elements in inorganic form to the soil and air. Some elements are also returned as the by-products of plant and animal metabolism. Ecosystems Ecosystems Biomass is the term ecologist use to refer to the amount, or mass, of living organic material in an ecosystem. Primary production is the amount of solar energy converted to chemical energy (organic compounds) by an ecosystem’s producers for a given area and during a give time period. It can be expressed in units of energy or of mass. The primary production of the entire biosphere is 170 billion tons of biomass per year. Different ecosystems vary considerably in their primary production as well as in their contribution to the total production of the biosphere. Net primary production refers to the amount of biomass produced minus the amount used by producers as fuel for their own cellular respiration. Gross production- respiration = net production (GP-R=NP) Ecosystems •Tropical rainforests are among the most productive terrestrial ecosystems and contribute a large portion of the planet’s overall production of biomass. •Coral reefs also have very high production, but their contribution to global production is small because they cover such a small area. •Even though the open ocean has very low production, it contributes the most to Earth’s total net primary production because of its huge size- it covers 65% of Earth’s surface Ecosystems Pyramid of Production Illustrates the cumulative loss of energy with each transfer in a food chain. Each tier of the pyramid represents one trophic level, and the width of each tier indicates how much of the chemical energy of the tier below is actually incorported into the organic matter of that trophic level. Note that producers convert only about 1% of the energy in the sunlight available to them to primary production. In this idealized pyramid, 10% of the energy available at each trophic level becomes incorporated into the next higher level. The efficiencies of energy transfer usually range from 5 to 20%. In other words, 80 to 95% of the energy at one trophic level never transfers to the next. Ecosystems Ecosystems Pyramid of Production An important implication of the stepwise decline of energy in a trophic structure is that the amount of energy available to top-level consumers is small compared with that available to lower-level consumers. Only a tiny fraction of the energy stored by photosynthesis flows through a food chain to a tertiary consumer, such as a snake feeding on a mouse. This explains why top-level consumers such as lions and hawks require so much geographic territory; it takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production. This also explains why there is less biomass and fewer numbers of organisms in higher trophic levels. Ecosystems Life depends on the recycling of chemicals. Because chemical cycles involve both biotic and abiotic components, they are called biogeochemical cycles. General scheme for the cycling of a nutrient within an ecosystem: 1. Producers incorporate chemicals from the abiotic reservoir into organic compounds. 2. Consumers feed on the producers, incorporating some of the chemicals into their own bodies. 3. Both producers and consumers release some chemicals back to the environment in waster products (CO2 and nitrogen wastes of animals). 4. Detritivores play a central role. As organisms die, these decomposers return chemicals in inorganic form to the soil, water, and air. The producers gain a renewed supply of raw materials, and the cycle continues. Ecosystems Biogeochemical cycles: Water cycle Carbon cycle Nitrogen cycle Phosphorous cycle Ecosystems Carbon cycle: Carbon is the major ingredient of all organic molecules. Like water, the element carbon has an atmospheric reservoir and cycles globally. Other abiotic reservoirs of carbon include fossil fuels, dissolved carbon compounds in the oceans, and sedimentary rocks such as limestone. The reciprocal metabolic processes of photosynthesis and cellular respiration are mainly responsible for the cycle of carbon between the biotic and abiotic worlds. Carbon compounds in detritus-animal wastes, plant litter, and dead organisms of all kinds—are consumed and decomposed by detrivores, and detritivore respiration, along with that of plants, animals, and other organisms, returns CO2 to the atmosphere. On a global scale, the return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis. However, the increased burning of wood and fossil fuels (coal and petroleum) is raising the level of CO2 in the atmosphere. This is appears to be leading to the significant problem of global warming. Ecosystems The Greenhouse Effect Greenhouse Effect: a natural phenomenon caused by the release of greenhouse gases, which act as a thermal blanket in the atmosphere, letting in sunlight, but trapping the heat that would normally radiate back into space About 75% of the natural greenhouse effect is due to water vapor. The next most significant contributor is carbon dioxide. In the past, our climate has shifted between periods of stable warm conditions to cycles of ice ages and “interglacials.” The current period of warming is explained in part by recovery after the last ice age 10,000 years ago. However there are many indications that climate warming is accelerting and that this acceleration is partly the result of human activity, in particular, the release of greenhouse gases into the atmosphere. The Greenhouse Effect Sources of Greenhouse Gases: Carbon dioxide Exhaust from cars, combustion of coal, wood, oil, and burning rainforests Methane Plant debris and growing vegetation, bleching and flatus of cows Chloro-fluoro-carbons (CFCs) Leaking coolant from refrigerators and air conditioners Nitrous oxide Car exhaust Tropospheric ozone (found in the lower atmosphere) Triggered by car exhaust (smog) The Greenhouse Effect What are the consequences? Recent data from the UN Environment Programme, based on studies of glaciers across nine mountain ranges, indicates that average glacial shrinkage is accelerating. Moreover, the rates of summer melting of Arctic ice are exceeding early predictions, leading to new forecasts predicting an ice-free Arctic by as early as 2013. Ice sheet shrinkage has a feedback effect too, because ice increases the amount of heat reflected back from the Earth. The effect of global warming on the Earth’s systems is likely to be considerable. The Greenhouse Effect Potential Effects of Global Warming Sea levels Expected to rise by 50 cm by the year 2100 Result of the thermal expansion of ocean water and melting glaciers and ice shelves. Warming may also expand habitat for many pests, e.g. mosquitoes, shifting the range of infectious disease. Forests Higher temps and precipitation changes could increase forest susceptibility to fire, disease, and insect damage. Forest fires release more carbon into the atmosphere and reduces the size of carbon sinks. A richer CO2 atmosphere will reduce transpiration in plants. Weather patterns May cause regional changes in weather patterns such as El Nino and La Nina, as well as affecting the intensity and frequency of storms. Driven by higher ocean surface temperatures, high intensity hurricanes no occur more frequently. The Greenhouse Effect Water resources Changes in precipitation and increased evaporation will affect the water availability for irrigation, industrial use, drinking, and electricity generation. Agriculture Climate change may threaten the viability of important crop-growing regions. Paradoxically, climate change can cause both too much and too little rain. The ice-albedo effect Ice has a stabilizing effect on global climate, reflecting nearly all the sun’s energy that hits it. As polar ice melts, more of that energy is absorbed by the Earth. The Greenhouse Effect The Precautionary Principle states that if an action or policy has a suspected risk of causing harm to the public or to the environment, in the absence of scientific consensus that the action or policy is harmful, the burden of proof that it is not harmful falls on those taking the action. allows policy makers to make discretionary decisions in situations where there is the possibility of harm from taking a particular course or making a certain decision when extensive scientific knowledge on the matter is lacking. implies that there is a social responsibility to protect the public from exposure to harm, when scientific investigation has found a plausible risk. These protections can be relaxed only if further scientific findings emerge that provide sound evidence that no harm will result. The Greenhouse Effect The Precautionary Principle (continued): “In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation”~United Nations Conference on Environment and Development Should the health and wealth of future human generations be jeopardized? Is it right to knowingly damage the habitat of, and possibly drive to extinction, species other than humans? Populations Population: a group of individuals of a single species that occupy the same general area. These individuals rely on the same resources, are influenced by the same environmental factors, and have a high likelihood of interacting and breeding with one another. Most of our knowledge of population dynamics comes from studies of much smaller groups that are confined by more restricted geographic boundaries—for instance, a population of binds on an island, or fish in a lake, or protists in a laboratory culture. Populations Population density is the number of individuals of a species per unit area or volume. For example, the number of oak trees per square kilometer (km2) in a forest, or the number of earthworms per cubic meter (m3) in forest soil. To measure population density, ecologists use a variety of sampling techniques to estimate population densities. In most cases, it is impractical or impossible to count all individuals of a population. Sampling Techniques: Point Sampling Transect Sampling Quadrat Sampling Mark and recapture (capture-recapture) Populations Mark and recapture (capture-recapture) Animals are captured, marked, and then released. After a suitable time period, the population is resampled. The number of marked animals recaptured in a second sample is recorded as a proportion of the total. Useful for: determining total population density for highly mobile species in a certain area (e.g. butterflies). Movements of individuals in the population can be tracked (especially when used in conjunction with electronic tracking devices). Considerations: time consuming to do well. Not suitable for immobile species. Population should have a finite boundary. Period between samplings must allow for redistribution of marked animals in the population. Marking should present little disturbance and should not affect behavior. Populations Mark and recapture (capture-recapture) Steps: 1. The population is sampled by capturing as many of the individuals as possible and practical. 2. Each animal is marked in a way to distinguish it from unmarked animals (unique mark for each individual not required). 3. Return the animals to their habitat and leave them for a long enough period for complete mixing with the rest of the population to take place. 4. Take another sample of the population (this does not need to be the same sample size as the first sample, but it does have to be large enough to be valid). 5. Determine the numbers of marked to unmarked animals in the second sample. Use the following equation (The Lincoln Index) to estimate the size of the overall population: Population size= (n1 x n2)/n3 n1= number of individuals initially caught, marked, and released n2=total number of individuals caught in the second sample n3= number of marked individuals in the second sample. Populations Within a population’s geographic range, local densities may vary greatly. The dispersion pattern of a population refers to the way individuals are spaced within their area. These patterns are important characteristics for an ecologist to study, since they provide insights into the environmental effects and social interactions in the population. Clumped Uniform Random Populations Clumped pattern Most common in nature Individuals are aggregated in patches Often results from an unequal distribution of resources in the environment. For example, plants or fungi may be clumped in areas where soil conditions and other factors favor germination and growth. Clumping of animals is often associated with uneven food distribution or with mating or other social behavior. For example, fish are often clumped in schools, which may reduce predation risks and increase feeding efficiency. Mosquitoes often swarm in great numbers, increasing their chances for mating. Populations Uniform, or even, pattern Pattern of dispersion often results from interactions between the individuals of a population. For example, some plants secrete chemicals that inhibit the germination and growth of nearby plants that could compete for resources. Animals may exhibit uniform dispersion as a result of territorial behavior. For example, penguins and humans Populations Random dispersion Individuals in a population are spaced in a patternless, unpredictable way. For example, clams living in a coastal mudflat might be randomly dispersed at times of the year when they are not breeding and when resources are plentiful and do not affect their distribution. Varying habitat conditions and social interactions make random dispersion rare. Populations Population size The number of individuals comprising a population may fluctuate over time. These changes make populations dynamic. A population in equilibrium has no net change in its abundance. Population Growth = B – D + I – E • Factors that influence the number of individuals in a population: – Birth (B) also known as natality – Death (D) also known as mortality – Immigration (I) – Emigration (E) Populations Life Tables Used to determine the average lifespan of various plants and animal species to study the dynamics of population growth. http://www.ssa.gov/OACT/STATS/table4c6.html Survivorship curves Graphs generated from life tables to make the data easier to comprehend. Plot the proportion of individuals alive at each age. • Type 1- produce few offspring, take care of their young, many survive into maturity. • Type 2- intermediate, more constant mortality over the entire life span. • Type 3- high death rates for the very young, mature individuals survive longer, usually involves very large # of offspring with little or no parent care Populations Three types of survivorship curves Populations The Exponential Growth Model The rate of population increase under ideal conditions. (High Birth Rate, Low Death Rate) Gives an idealized picture of unregulated population growth; no population can grow exponentially indefinitely. The whole population multiplies by a constant factor during each time interval. The simple equation G=rN describes this J-shaped curve G : growth rate of the population (the number of new individuals added per time interval) N: stands for the population size (the number of individuals in the population at a particular time) r: intrinsic rate of increase; remains constant (maximum capacity of members that population to reproduce) Populations Logistic Growth Model A description of idealized population growth that is slowed by limiting factors as the population size increases. Limiting factors are environmental factors that restrict population growth. G=rN(K-N)/K K= carrying capacity (maximum population size that a particular environment can support or “carry”). S-shape curve 1. Exponential Growth Phase-When the population first starts growing, N is very small compared to the carrying capacity K. Population growth is close to exponential growth; (K-N)/K nearly equals K/K or 1 2. Transitional Phase- The population growth starts to slow; N gets closer to carrying capacity, the term (K-N)/K becomes an increasingly smaller fraction. 3. Plateau Phase- Carrying capacity is reached and the population is as big as it can theoretically get in its environment; N=K, therefore (K-N)/N=0, therefore G=O. Populations Logistic Growth Curves Populations What does the logistic growth model suggest to us about real populations in nature? Model predicts that a population’s growth rate will be small when the population size is either small or large, and highest when the population is at an intermediate level relative to the carrying capacity. Small Population: resources are abundant, and the population is able to grow nearly exponentially. The increase is small because N is small. Large Population: limiting factors strongly oppose the population’s potential to increase. These limiting factors cause the birth rates to decrease, the death rate to increase, or both. Eventually, the population stabilizes at the carrying capacity (K), when the birth rate equals the death rate. **It is important to realize that this is a mathematical model…no natural populations fit perfectly!** Populations Factors that appear to regulate growth in natural populations: Density-dependent factors: Competition among members of a growing population for limited resources, like food or territory. Health of organisms Predation Physiological factors (reproduction, growth, hormone changes) Density independent factors • Regardless of population density, these factors affect individuals to the same extent. – Weather conditions – Acidity – Salinity – Fires – Catastrophies Populations Life History is the series of events from birth through reproduction to death. For a given population in a particular environment, natural selection will favor the combination of life history traits that maximizes an individual’s output of viable, fertile offspring. Key life history traits: Age at which reproduction first occurs Frequency of reproduction Number of offspring Amount of parental care given. Populations Life History (continued) Some ecologists hypothesize that different life history patterns are favored under different population densities and conditions. r-selection (r-strategies) Individuals mature early produce a large number of offspring at a time. Usually only reproduce once. Have a small body size Have a short life span For example, insects and weeds K-selection (K-strategies) Typically larger-bodied Long life span, late maturity Reproduction occurs at a later age with the production of a few, well-cared for offspring. Usually reproduce more than once. Common in populations that live at densities close to the carrying capacity (K) of their environment. Example: many large terrestrial vertebrates Populations Life history (continued) There are organisms that display either extreme r- or K- strategies, but most organisms have life histories that are intermediate on the continuum. Some organisms such as Drosophila switch strategies depending on environmental conditions: In a predictable environment In order to maximize fitness, it pays to invest resources in long-term development and long life (K-strategy) In an unstable environment It is better to produce as many offspring as quickly as possible (r-strategy) *ecological disruption favors r-strategists such as pathogens and pest species Impacts of Humans on Ecosystems Statospheric Ozone Depletion Loss of biodiversity Endangered Species Impact of Alien Species Fisheries Management Impacts of Humans on Ecosystems Stratospheric Ozone Depletion Ozone (O3) is found in a band of the upper stratosphere as a renewable thin veil. It absorbs about 99% of the harmful incoming UV radiation from the sun and prevents it from reaching the Earth’s surface. An increase in UV-B radiation is likely to cause immune system suppression in animals, lower crop yields, a decline in the productivity of forests and surface dwelling plankton, more smog, changes in the global climate, increasingly severe sunburns, increase in skin cancers, and more cataracts of the eye. Ozone is being depleted by a handful of human-produced chemicals: CFCs appear to be the primary cause for ozone depletion. UV light hits a CFC molecule and releases a chlorine atom. Chlorine reacts with ozone, forming a Chlorine oxide molecule. This interferes with ozones ability to renew itself, causing holes in the ozone layer. Impacts of Humans on Ecosystems Impacts of Humans on Ecosystems Loss of Biodiversity Biodiversity is measured by species. It is not distributed evenly on Earth, being consistently richer in the tropics and concentrated more in some areas than in others. Biodiversity hotspots are located in the tropics and most are forests. Loss of biodiversity reduces the stability and resilience of natural ecosystems and decreases the ability of their communities to adapt to changing environmental conditions. Impacts of Humans on Ecosystems Endangered Species Species under threat of severe population loss or extinction are classified as either endangered or threatened. An endangered species is one with so few individuals that it is at high risk of local extinction, while a threatened (or vulnerable) species is likely to become endangered in the near future. For example, hunting and collecting are one cause of species decline. Black Rhinoceros were once plentiful throughout much of Africa. Now, only remnant populations remain. In Kenya, 98% of the population was lost in only 17 years. Conservationists suspect that a trader with a large stockpile of horn is trying to cause rhinoceros extinction in order to increase the horn’s value. Impacts of Humans on Ecosystems Impact of Alien Species Alien species is a term used to describe those organisms that have evolved at one place in the world and have been transported by humans, either intentionally or in advertently, to another region. Some of these alien species are beneficial e.g. introduced agricultural plants and animals, and Japanenese clams and oysters Invasive species are those alien species that have a detrimental effect on the ecosystems into which they have been imported. They number in their hundreds with varying degrees of undesirability to humans. Humans have brought in may exotic species into new environments for use as pets, food, ornamental specimens or decoration, or through cargo shipments. Some have been deliberately introduced to control another pest species and have themselves become a problem. The most destructive are aggressive plants, eg. Mile-a-minute weeda perennial vine from Central and South America, miconiaa South American tree invading Hawaii and Tahiti, and Caulerpa seaweedthe aquarium strain now found in the Mediterranean. Impact of Humans on Ecosystems The Impact of Alien Species (continued) An example of an alien species, and impact it had on ecosystem: The introduction of the brushtail possum into New Zealand, where it has severely damaged forest ecosystems throughout the country, feeding on palatable tree species, preventing regeneration, and decimating native populations of invertebrates and birds. An example of biological control of an invasive species: The biological control of the prickly pear cactus in Australia by the caterpillar of the moth Cactoblastis cactorum, which feeds directly on the cactus flesh. Control of the cactus by the caterpillar has been a spectacular success and now only scattered populations of the cactus occur. Impacts of Humans on Ecosystem Fisheries management Stocks of commercially fished species must be managed carefully to ensure that the catch (take) does not undermine the long term sustainability of the fishery. This requires close attention to stock indicators, such as catch per unit of fishing effort, stock recruitment rates, population age structure, and spawning biomass. Impacts of Humans on Ecosystems Fisheries Management Fishing is a human tradition that not only satisfies a need for food, but is economically, socially, and culturally important. Decades of overfishing in all of the world’s oceans has pushed commercially important species (such as cod) into steep decline. The UN’s Food and Agriculture Organization (FAO) reports that almost seven out of ten of the ocean’s commercially targeted marine fish stocks are either fully or heavily exploited (44%), overexploited (16%), depleted (6%), or very slowly recovering from previous overfishing (3%). The maximum sustainable yield: the largest yield (or catch) that can be taken from a species' stock over an indefinite period has been exceeded by too many fishing vessels catching too many fish, often using wasteful and destructive methods. Impacts of Humans on Ecosystems Fisheries Management Stock Indicators: For example, the stock of North Sea cod (Gadus morhua) is one of the world’s six large populations of the economically important species. As one of the most intensively studied, monitored, and exploited fish stocks in the North Sea, it is considered a highly relevant indicator of how well sustainable fisheries policies are operating. Stocks of commercially fished species must be managed carefully to ensure that the catch (take) does not undermine the long term sustainability of the fishery. This requires close attention to stock indicators, such as catch per unit of fishing effort, stock recruitment rates, population age structure, and spawning biomass. Currently, the North Sea cod stock is below safe biological limits and stocks are also depleted in all waters adjacent to the North Sea, where the species is distributed. Recent emergency measures plant to arrest this decline. Impacts of Humans on Ecosystems Fisheries Management Stock indicators (continued): What is being done? A large part of the North Sea was closed for cod fishing between February and April 2001, to protect juvenile cod. The TAC (total allowable catch) has been set at approximately half that set for the year 2000. Further regulations, such as increasing net mesh size and reducing the volume of fish discarded, are planned, and will further restrict the effort of fishing fleets until (if) the stock recovers. The ICES (the International Council for the Exploration of the Sea) has recommended a recovery plan that will ensure recovery of the spawning stock to a level of more than 150 000t. Reduction in TAC alone are insufficient to stop the declines. Conservation of Biodiversity Conservation on a national scale generally involves setting up reserves or protected areas to slow the loss of biodiversity. Nature reserves may be designated by government institutions in some countries or by private landowners. The different types of nature reserves, e.g. wildlife, scenic and scientific reserves, and National Parks, all have varying levels of protection depending upon country and local laws. Conservation of Biodiversity The Nature Conservancy is an agency concerned with monitoring and managing the loss of biodiversity. The mission is to preserve the plants, animals, and natural communities that represent the diversity of life on Earth, by protecting the lands and waters they need to survive. With donations from over a million members, the Conservancy has purchased 12,621,000 acres in the USA and a further 96,286,000 acres outside the USA. Larger nature reserves usually promote conservation of biodiversity more effectively than smaller ones. The ecology of the edges of ecosystems is different from the central areas due to edge effects. An example of an edge effect is the egg-laying habits of the cowbird of the western U.S. It feeds in open areas, but it lays its eggs in the nests of other birds near the edges of forests. Fragmentation of forests has led to a considerable increase in cowbird populations because of the increase in forest edge. Wildlife corridors allow organisms to move between different parts of a fragmented habitat, for example, tunnels under busy roads. Conservation of Biodiversity Active management strategies in conservation of an endangered species: Mainland Island Management: A new strategy in conservation involves intensive management of species within a well defined area. These programs have a goal of comprehensive ecosystem restoration, with species recovery being an important consideration. In New Zealand, this strategy has been used very successfully to restore populations of the endangered wattled crow, kokako. Kokako are at risk through forest clearance and predation by introduced mammals, especially during the nesting season. Kokako recovery was implemented in a specified area of native forest which was large enough to sustain a viable population but small enough to implement long term pest control. These mainland island projects involve very intensive pest control programs and continued monitoring of both pest populations and the species under threat. Such programs are costly but effective; through intensive ecosystem management, the kokako population decline had been reversed and chicks now survive to breed. Conservation of Biodiversity in situ conservation of endangered species Habitat protection and restoration Most countries have a system of parks and reserves focused on whole ecosystem conservation. These areas aim to preserve habitats with special importance and they may be intensively managed through pest and weed control programs, revegetation, and reintroduction of threatened species. ex situ conservation measures Captive breeding and relocation Individuals are captured and bred under protected conditions. If breeding programs are successful and there is suitable habitat available, captive individuals may be relocated to the wild where they can establish natural populations. Zoos, botanical gardens, and gene banks Many zoos specialize in captive breeding programs, while botanical gardens raise endangered plant species. Universities and government agencies participate by providing practical help and expertise. Gene banks around the world have a role in preserving the genetic diversity of species.