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Environmental Science A Study of Interrelationships Eleventh Edition Enger & Smith Chapter 5 Interactions: Environments and Organisms Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Interactions: Environments and Organisms Outline Ecological Concepts Natural Selection and Evolution Organism Interactions Community and Ecosystem Interactions Ecological Concepts Ecology is the study of ways organisms interact with each other and with their nonliving surroundings. Deals w things such as ways of adapting to surroundings, how make use of surroundings, how an area is altered by presence & activities of organisms. Interaction require E and matter. Living things need E & matter to survive. Organism depend on each other for that, so ecology can be divided in several special fields Environment means everything that affects an organism during its lifetime. • Biotic factors: Living components. All forms of life with which the organism interacts. • Some categories include photosynthetic plants, animals that eat others, bacteria & fungi that cause decay, bacteria, viruses and parasitic organisms cause disease. • Abiotic factors: Nonliving things that influence an organism, such as energy, nonliving matter, living space, and ecological processes. • All livings need a source of E & sun is the ultimate source of E for almost all organisms. • All forms of life require atoms of elements such as C, N, P & molecules such as water to construct & maintain themselves. • These elements r obtained from env & r returned to env through respiration, excretion, death & decay. • Structure & location of the space organisms inhabit r important abiotic aspect of env. Some live at sea level some in mountains & high levels, some env r homogeneous others r jumble of rocks… • Climate is another important factor. It’s the result of interaction of matter & E & is determined by factors such as amount of solar radiation, proximity to equator, patterns of wind . Ecological Concepts Levels of organization in ecology Ecology deals w interaction between organisms & env & can take place at different levels from ecosystem level through community interactions to population studies & study of niche of individual organism. Ecology also involves study of physical env & atoms & molecules that make up living & nonliving parts. Limiting Factors All organisms interact w their surroundings & certain factors may be critical to particular species success. Limiting factors are any factors whose shortage or absence restricts species success. They can be biotic/abiotic, & can be quite different from one species to another. Ex sunlight, water, nutrients for plants, oxygen in water for fish • Scarcity of water or specific nutrients (plants) • Climate, availability of a specific food (animals). Each species has a Range of tolerance indicates a range of conditions in which an organism can survive. – Temperature – pH Ecological Concepts Limiting factors (connection bet T (limiting factor) and reptiles popn) Ecological Concepts Limiting factors Habitat and Niche Env influences organism & organism influence env. The habitat of an organism is the space in which an organism lives; it is defined by the biological requirements of each particular organism (organism address). • Usually highlighted by prominent physical or biological features. Ex mosses: small plants, must be covered w thin layer of water to produce, if exposed to sunlight, wind, drought they die. So typical habitat is cool, moist & shady The niche of an organism is the functional role (profession) the organism has in its surroundings. • This term includes all the ways an organism affects the organisms with which it interacts as well as how it modifies its physical surroundings. Habitat and Niche Moss habitat Ecological Niche Ecological niche is complex set of interactions between organism & its env & includes all the ways an organism influences its surroundings as well as the ways it is affected by env. A beavers ecological niche includes building dams, flooding forested areas, providing protection for them, killing trees, providing habitat for ducks & other animals, serving as food for predators & many other effects. Habitat and Niche Ecological niche of a beaver Genes, Populations, and Species Genes are distinct pieces of DNA that determine the characteristics an individual displays. Such as leaf shape, feather color A population includes all organisms of the same kind found within a specific geographic region. • A population contains more kinds of genes than any single individual within the population. Genes are passed from one generation to the next through reproduction. A species is a population of all the organisms potentially capable of reproducing naturally among themselves and having offspring that also reproduce. An individual organism is a member of a species. • Working definition that only applies to organisms that sexually reproduce. –Some species are easy to recognize, while others are more difficult. Humans vs mosquitoes –3 points in this definition of species: – some individuals in any popn will never reproduce & many pairs never meet one another but have still potential to interbreed – Ability to produce fertile offspring. 2 kinds of organisms may interbreed & produce offspring but offspring r sterile & never reproduce so they r not same species. Ex horses & donkeys produce mules that r sterile – Some organisms reproduce primarily by asexual reproduction, not mate just reproduce copies of themselves. These not fit in this definition. However most organisms reproduce asexually as well as sexually & can be assigned to a species based on time they mate Natural Selection Each species of organism is specifically adapted to a particular habitat in which it has a specific role. But how they fit in a specific role in such a precise way? The process that fit organisms characteristics w the demands of its env is known as: Natural selection is the process that determines which individuals within a species will reproduce and pass their genes to the next generation. Because genes r determinant of structural, physiological & behavioral characteristics of organisms. The changes seen in the genes and characteristics displayed by successive generations of a population of organisms over time is known as evolution. Natural Selection Several conditions and steps are involved in the process of natural selection: 1. Individuals within a species show genetically determined variation. Some r useful some not. Some color of animals make them conspicuous others not 2. Organisms within a species typically produce more offspring than are needed to replace the parents when they die. Most of the offspring die. 3. The excess number of individuals results in a shortage of specific resources. They compete for food, space, mates or other things that r limited. Natural Selection 4. Due to individual variation, some individuals have a greater chance of obtaining needed resources and therefore have a greater likelihood of surviving and reproducing than others. 5. As time passes, the percentage of individuals showing favorable variations will increase while the percentage showing unfavorable variations will decrease. Evolutionary Patterns When we look at the effects of natural selection over time, we see changes in the characteristics of a species & kinds of species present. Some changes take milin of years, others few years. We have to remember as env change species change, some species can adapt some not. Evolution - A change in the kinds of organisms that exist and in their characteristics. Study of fossil records show as new species come into being, other species disappear. This is called Speciation - Production of new species from previously existing species. • Thought to occur as a result of a species dividing into two reproductively isolated subpopulations. • If 2 subpopulations have some genetic differences & their env r different, natural selection will work on them differently & they will begin to diverge from each other. • Eventually differences become so great that 2 subpopulation can not interbreed & become 2 different species. • In plants polyploidy results in new species happens when the # of sets of chromosomes in the cells of plants is increased. • Many organisms r diploid=2 set of chromosomes; one from each parent, one in egg, one in sperm. • Polyploid organism have several sets. Ex many plants have extra sets of chromosomes & cant produce w closely related species w different # of sets of chromosomes Evolutionary Patterns Env keep changing, species w lack of genetic resources to cope w these changes go extinct. Extinction - Loss of entire species. • Of estimated 500 million species believed to have ever existed on earth, 98-99% have gone extinct. • Studies of fossils & geological features show only thousands years ago huge glaciers covered much Europe & N America. • Humans coexisted w mammoths, saber-toothed tigers & giant cave bears. • As climate became warmer glaciers receded, humans continued to prey on these animals causing mammoths, saber-tooted tigers & giant cave bears to extinct. Humans, horses & some plants that adapted survived. • It is possible to have extinction of specific popn of a species, ex small local popn can easily go extinct this can result in loss of specific gene combinations • Natural selection work to shape organisms to fit a changing env • Human have a significant impact on extinction of many kinds of species • Modification of env by human for their purposes, introduction of exotic species has caused displacement of species from the area • Humans r also subject to evolution & might go extinct Co-Evolution - Two or more species can reciprocally influence the evolutionary direction of the other. In other words, organisms affect evolution of other organisms. • Ex Grazing animals and grass species. Grasses eaten by animals grow from the base rather than from tips & have hard materials in their cell walls making it difficult for animals to crush the cell walls and digest them • Animals have teeth that r very long or grow continuously to compensate for the wear associated w grinding hard materials • Others have complicated digestive tracts allow microorganisms to do digestion Kinds of Organism Interactions Ecologists study how organisms interact w each other. One common kind of interaction is Predation is a kind of interaction in which one animal kills/eats another. • Predator benefits from food. & prey is harmed. Ex lions & zebras, robins & earthworms, venues flytrap & insects • Prey adaptation is manifested in a higher reproduction rate. • Predator uses several strategies: – strong & speedy ones chase & overpower prey, – others lie in wait & quickly strike, – some use snares to catch • prey tries to avoid predation: – Some have keen senses to detect predators, – others camouflage, – many remain motionless Prey adaptation is manifested in a higher reproduction rate. Kinds of Organism Interactions • Individual organisms that is killed & eaten is harmed (old & slow ones) but not the prey species • Prey species benefits by eliminating non-adaptive genes from the gene pool. Individuals that are best adapted will survive & reproduce offsprings w better survival characteristics – Poorly adapted predators are less likely to obtain food and thus pass on non-adaptive genes. They not survive to reproduce Competition Competition is a kind of interaction in which two organisms strive to obtain the same limited resource and both are harmed to some extend. Ex trees growing close to each other, both get less nutrients. • Intraspecific competition is competition between members of same species. Corn plants competing for water & nutrients in a field • Interspecific - Members of different species competing for resources. Ex foxes & coyotes use same prey species=mice/rabbit, if shortage of supply certain predator may be more successful than others The more similar the competing species, the more intense the competition. If one of two competing species is better adapted to live in the area, less fit one must • evolve into a slightly different niche, • migrate to different geographic area, • or become extinct. This is called Competitive Exclusion Principle. Competition The competitive exclusion principle holds that no two species can occupy the same ecological niche in the same place at the same time. • Less-fit species must evolve into a slightly different niche. • Examining niche requirements of two similar species show significant differences between their niches which reduces intensity of the competition between them • Ex many birds eat insects, but may obtain them in different ways: woodpecker excavates openings to obtain insects in rotting wood, warblers flit about in the foliage capturing insects. Symbiotic Relationships Symbiosis is a close, long-lasting, physical relationship between two different species. At least one species derives benefit from the interaction. There are three categories of symbiotic relationships: • Parasitism • Commensalism • Mutualism Symbiotic Relationships Parasitism is a relationship in which one organism (parasite) lives in or on another organism (host), from which it derives nourishment. Host is not killed immediately. • Some parasites more destructive, both evolve in such a way that they can accommodate one another. Host evolves defenses against parasite to reduce the harm, • Many parasites have complex life that involves more than one host for different stages in its life cycle. Ex many worm parasites have adult, reproductive stage in a carnivore but immature stage in another animal that carnival uses as food (dog tapeworm) • Some parasite life cycles involve animals that carry the parasite from one host to another. • These carriers known as vectors. Ex biting insect & mites can transmit parasites when they obtain blood meal • Malaria, lyme disease, sleeping sickness are transmitted by vectors • Ectoparasites live on the host’s surface. – Fleas, lice, molds, mildews • Endoparasites live inside the body of the host. – Tapeworms, malaria parasites, bacteria, fungi How about plants? Mistletoe is parasite of some trees, birds transfer the seed to tree Symbiotic Relationships Commensalism is a relationship in which one organism benefits while the other is not affected. A parasitism relationship may evolve into a commensal one if the host is not harm at all. • Remoras and sharks • Many commensal relationships r rather opportunistic & may not involve long-term physical contact. Ex birds use trees to build nest but not use the same tree year after year Mutualism is a relationship in which both species benefit. The relationship is obligatory in many cases, as neither can exist without the other. Or even if they can, it is more successful when together • Mycorrhizae • many kinds of fungi form an association w roots of plants called Mycorrhizae. Fungi obtain organic molecules form roots and fungus assists plant in obtaining nutrients such as phosphates & nitrates • Some relationships r hard to identify & categorize, mosquito/tick=temporary parasites/blood predators • Difficult to fit in other category: relationship between certain birds such as cowbirds & European cuckoos that not build nest & lay egg in nests of others to care for in the expense of their own nestlings who generally die=nest parasitism Symbiotic Relationships Examples of symbiotic relationships Community and Ecosystem Interactions Humans have complicated relationship w other organisms which can be placed in same categories: predator, herbivore, scavenger, commensalism (using shade of tree), parasitism (Africa blood of cow drawn mixed w milk), mutualism (domesticated plants), competition (w all organism) Two concepts that focuses on relationships that involve many different kinds of interactions r community & ecosystem Community and Ecosystem Interactions A community is an assemblage of all interacting species of organisms in an area. Ex in prairie, grasses have major role since they do photosynthesis & provide food & shelter for others; grasshoppers, prairie dogs & bison's r imp consumers; meadowlarks consume insects but have minor role; bacteria & fungi provide nutrients An ecosystem is a defined space in which interactions take place between a community, with all its complex interrelationships, and the physical environment. Physical world has major impact on kinds of plant & animal in an area as well as the kind of soil & amount of moisture At the same time organism also impact their physical surroundings While concepts of community & ecosystem r closely related but ecosystem is a broader concept because involves physical as well as biological processes Ecosystem has parts that must be organized in specific ways or the systems will not operate, so we will look at ecosystems from 3 points of view: • major role played by organisms, • the way E is utilized w/in ecosystems, • the way atoms r cycled from one organism to another Major Roles of Organisms in Ecosystems Ecologists have divided organisms’ roles in ecosystems into three broad categories: 1. Producers: Organisms that are able to use sources of energy to make complex organic molecules from simple inorganic substances in their environment. Plants, algae, phytoplankton (aquatic organism) 2. Consumers: Organisms that require organic matter as a source of food. They consume organic matter to provide themselves with energy and organic molecules necessary for growth and survival. An important part of their role is the process of respiration= braking organic matter to inorganic one Major Roles of Organisms in Ecosystems • Consumers can be further divided into categories based on the things they eat and the way they obtain food. – Primary consumers, or herbivores, eat plants as a source of food. – Secondary consumers, or carnivores, are animals that eat other animals. – Omnivores consume both plants and animals. 3. Decomposers use nonliving organic matter as a source of energy and raw materials to build their bodies. Many small animals, bacteria, and fungi fill this niche. – Since decomposers carry on respiration, they r extremely important in recycling matter by converting organic matter to inorganic material. Keystone Species Although there r many species interacting w each other and their env, some r more important. A keystone species plays a critical role in the maintenance of specific ecosystems. • When bison are present in American tallgrass prairie ecosystems, they increase the biodiversity of the site. – Bison in American Tall Grass Prairie: grazing animal r extremely important in maintaining the mix of species of a grassland. – w/o them nature of prairie changes; present of bison will increase the biodiversity of the site, by eating tall grasses and allowing smaller plant species grow. – Bison dig holes in soil that support many species of plants that typically live in disturbed areas. – Their urine important source of nitrogen for plants. So not all species can be treated equally, some have pivotal role and their elimination or severe reduction can significantly alter ecosystem. – In some cases lost of K.S results in permanent modification of ecosystem to something totally different from original one. Energy Flow Through Ecosystems Ecosystem is a stable, self-regulating unit, it changes & need E for stability. Sunlight is significant E source trapped by producers and then become available to ecosystem and is stored in the form of chemical bonds in large organic molecules (carbohydrates, fat, protein) & is transferred to other organisms when eat producers. Each step in the flow of energy through an ecosystem is known as a trophic level. As energy moves from one trophic level to the next, most of the useful energy (90%) is lost as heat (second law of thermodynamics). • When E is passed from one trophic level to next, some useful E is lost, which dissipate to the surroundings and warms the air, water, or soil. • Since organisms must expend E to maintain life processes, amount of E contained in higher trophic levels is considerably less that that at lower levels. Because it is difficult to measure the amount of energy contained in each trophic level, biomass (weight of living material) is often used as a proxy to approximate the relationship between amounts of E at each level. Energy Flow Through Ecosystems E passes through several levels known as trophic levels. Each level has certain amount of E, each time E flow to another level, about 90% of useful E is lost, usually as heat to surroundings. So higher trophic levels contain less E & fewer organisms. Categories of organisms within an ecosystem. Food Chains and Food Webs A food chain is a series of organisms occupying different trophic levels through which energy passes as a result of one organism consuming another. • Some chains rely on detritus (small pieces of nonliving organic material). Ex bottoms of the deep lakes & oceans r 2 dark for photosynthesis, so organisms rely on a steady rain of small bits of organic matter from upper layers of the water where there is photosynthesis activity. A food web is a series of multiple, overlapping food chains. • More stable. A single predator can have multiple prey species at the same time. so if one is short it will switch to other ones. Food Chains and Food Webs Food chain Food web Food Chains and Food Webs Food chain Food web Nutrient Cycles in Ecosystems— Biogeochemical Cycles Organisms are composed of molecules and atoms that are cycled between living and non-living portions of an ecosystem. These nutrient cycles are called biogeochemical cycles. Some atoms (C, N, O, H, P) r more important. They r found in protein, DNA, carbohydrates, fats. Organic molecules contain large # of carbon atoms. These molecules r manufactured from inorganic molecules by producers & r transferred from one living organism to another in food chains. Processes of respiration & decay break down the complex organic molecules to simpler inorganic ones. We will look at flow of 3 kinds of atoms w/in communities & between biotic & abiotic part of ecosystem. Carbon Cycle All living things r composed of organic mol which r composed of C. 1. Carbon and oxygen combine to form carbon dioxide. 2. Plants use carbon dioxide during photosynthesis to produce sugars (algae & bacteria also perform photo). E for photo is provided by sunlight. Oxygen is released. So light E is converted to chemical-bond E in organic molecules. 3. Plants use sugars for growth & to provide E for other necessary process. 4. Herbivores eat plants, break down the complex organic molecules into simpler molecular building blocks, and incorporate those molecules into their structure. 5. Respiration breaks down organic molecules into CO2 and water and releases those compounds back into the atmosphere. –Almost all organisms perform Respiration which breaks down sugars releasing CO2 and water back into the atmosphere. »When an herbivore is eaten by a carnivore, some of the carbon-containing molecules get incorporated into their body and remaining organic molecules r broken down in process of respiration. In carbon cycle all organisms require organic molecules for their survival and must either manufacture them or consume them. In C cycle the same C atoms r used over & over. Same C cycle operates in aquatic systems. Carbon Cycle 6. The decay process of decomposers involves respiration and therefore recycles naturally occurring organic molecules. 7. Burning fossil fuels takes carbon atoms that were removed temporarily from the active, short-term carbon cycle and reintroduces them into the active cycle. Carbon Cycle Carbon atoms r cycled through ecosystems. Plants can incorporate carbon atoms from carbon dioxide into organic molecules when they carry on photosynthesis. The carbon containing organic molecules r passed to animals when they eat plants or other animals. Organic wastes or dead organisms r consumed by decay organisms. All organisms, plants, animals and decomposers return carbon atoms to the atmosphere when they carry on respiration. Oxygen atoms r being cycled at the same time that carbon atoms r being cycled. Carbon cycle Nitrogen Cycle 78% of the gas in the air we breath is made up of N & N cycle involve Cycling of nitrogen atoms between abiotic and biotic ecosystem components. • Producers are unable to use atmospheric N. They must make new N-containing molecules such as proteins & DNA. – Must get nitrate (–NO3) or ammonia (NH3.) so N containing compounds r often in short supply & its availability is a factor that limits the growth of plants. • Nitrogen-fixing bacteria convert nitrogen gas N2 into ammonia that plants use. • Some live freely in soil & r called free-living N-fixing bacteria, others r known as symbiotic N-fixing bacteria, have a mutualistic relationship w certain plants & live in nodules in roots of plants known as legumes & certain trees. • Some grasses & evergreen have similar relationship w certain root fungi. – Plants construct organic molecules (protein, DNA). – Eaten by animals. Plant protein molecules r broken down to smaller building blocks called amino acids which form proteins typical for herbivore. • Decomposers also break down nitrogen-containing molecules releasing ammonia. Nitrogen Cycle Nitrifying bacteria are able to convert ammonia to nitrite, which can be converted to nitrate & plants use as a source of N for synthesis of N-containing organic molecules. Denitrifying bacteria are able (under anaerobic conditions) to covert nitrite to nitrogen gas (N2) which is ultimately released into the atmosphere & enters the cycle by N-fixing bacteria. N-cycle has 2 significant differences from Ccycle: Most of the difficult chemical conversions r made by bacteria & other microorganisms, • 2nd although N enters organisms by way of N-fixing bacteria & returns to atmosphere through action of denitrifying bacteria, there is a 2ndary loop that recycles N compounds directly from dead organisms & wastes directly back to producers. In naturally occurring soil, N is limiting factor for plant growth & has to be supplied to soil. Farmers use alternative methods to supply N; ex alternate N yielding crops such as soybeans w N-demanding ones such as corn, or plants alternating strips of crops, or grow a N-fixing crop for a short period of time then plow crop into soil and let organic matter decompose them (green Manure). Also can spread manure from animal & rely on bacteria to decompose them and release N. Nitrogen Cycle Nitrogen cycle Phosphorus Cycle P is another important element in the structure of living things. It is present in many biological molecules such as DNA, cell membrane, bone, teeth. Phosphorus is not present in the atmosphere as a gas (important diff from N & C cycle). The ultimate source of phosphorus atoms is rock. 1. Phosphorus compounds are released by erosion and become dissolved in water. 2. Plants use phosphorus to construct necessary molecules. 3. Animals gain necessary phosphorus when they consume plants or other animals. 4. Decomposers recycle phosphorus compounds back into the soil after animal die or excrete waste. P dissolved in water r precipitated as deposits & geological processes elevate them & expose them to erosion, making them available to organism again. »Waste of animals have lots of P and places with tick layer of animal dropping, is a major source of P. »Many soils and aquatic ecosystems are short in P. »Fertilizers usually contain N, P, and K. »In agriculture ecosystems these elements are removed by harvesting crops and should be supplied by fertilizers. »Aquatic ecosystem are sensitive to nutrients level. »High level results in rapid growth. Phosphorus Cycle Rock is the source of P and when is dissolved provide it for plants & animals. Phosphorus cycle Human Impact on Nutrient Cycles Humans have significantly altered level of these nutrients. Two activities caused significant changes in carbon cycle: Burning of fossil fuels releases large amounts of carbon dioxide into the atmosphere. Converting forests (long-term carbon storage) to agricultural land (shortterm carbon storage) has increased the amount of carbon dioxide in the atmosphere. Converting forests to agricultural land causes less C being stored in the bodies of large, long-lived plants. Fossil fuel burning also increases the amount of nitrogen available to plants. When fossil fuels are burned, O & C are heated to high temperature and different kinds of N-containing compounds are produced which can be used by plants as nutrients. These have doubled level of N available. Human Impact on Nutrient Cycles If too much nitrogen or phosphorus is applied as fertilizer, or if it is applied at the wrong time, much of the fertilizer is carried into aquatic ecosystems. – Lowered oxygen concentrations. When organisms die, decomposers use O from water to break down dead organic molecules which lowers O. – This create a “dead zone” with few fish and bottom-dwelling organisms. Agricultural activities in US, causes death of fish in Gulf of Mexico. • The presence of these nutrients increases the growth rate of bacteria, algae, and aquatic plants. – Toxic algae can kill fish and poison humans. – An increase in the number of plants and algae results in lowered oxygen concentrations, creating “dead zones.” Summary An organism’s environment can be divided into biotic (living) and abiotic (nonliving) components. The space an organism occupies is its habitat, and the role it plays is its niche. Organisms interact with one another in a variety of ways. Symbiotic relationships are those in which two species live in physical contact and at least one species derives benefit from the relationship. In an ecosystem, energy is trapped by producers and flows from producers through various trophic levels of consumers. Summary The sequence of organisms through which energy flows is called a food chain. Multiple interconnecting food chains constitute a food web. The flow of atoms through an ecosystem involves all the organisms in a community. The carbon, nitrogen, and phosphorus cycles are examples of how these materials are cycled in ecosystems.