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Department
Environmental Studies
Course
ENVS 1500
Professor
Gail Fraser
Semester
Fall

Description
ENVS 1500 Fall Term Lecture 1 Readings Ecology, Concepts and Application (Molles, M.C. Jr. and Cahill, J.F.) Chapter 1 Notes (pg. 1-10) What is Ecology?  Ecology is the branch of science dedicated to the study of relationships between organisms and the environment.  The term ecology comes from the Greek word for house.  Much of ecology is focused on understanding how organisms interact with each other and their environment.  Ecology is an interdisciplinary science, and not a political philosophy or a way of life.  An ecologist is a person who applies a scientific approach to understanding the relationships between organisms and environment.  Ecology is about understanding the mechanisms causing the patterns that occur in the natural world. Overview of Ecology  The discipline of ecology addresses environmental relationships ranging from individual organisms to factors influencing the state of the entire biosphere.  Physiological ecologists study the morphological and physiological mechanism organisms use to gather energy and cope with biotic and abiotic stressors.  Behavioral ecologists focus principally on the determinants of individual behavior, and how that can influence interactions among individual and the environments.  Population ecology is centered on the factors influencing population structure and dynamics.  Community ecologists study interactions study interactions such as predations, parasitism, mutualism etc.  Ecosystem ecology is a broad scope of study including the biological, chemical, and physical process and interactions that occur within a location. One goal of ecosystem ecology is to understand the controls on nutrient cycling and energy flow through ecosystems.  The study of different exchanges is landscape ecology. ENVS 1500 Lecture 2 Readings Chapter 7 Notes (pg. 169-181; 191-194) Energy sources  Organisms use one of the three main sources of energy 1. Solar, radiation 2. Organic molecules 3. Inorganic molecules  Organisms obtain energy by trophic (feeding) biology  Organisms that use inorganic sources of both carbon and energy are called autotrophs (self-feeders), there are two types 1. Photosynthetic: use carbon dioxide as a source of energy (plants, protists) 2. Chemosynthetic: use inorganic molecules as a source of carbon and as a source of energy  Heterotrophs (other feeders) are organic molecules both as a source of carbon and as a source of energy (e.g. bacteria, fungi, protists etc.  Prokaryotes have no cells with membrane-bound nucleus or organelles  Archae are known to be widely spread in the biosphere especially oceans  Protists are either photosynthetic or heterotopic  Most plants are photosynthetic  All fungi and animals are heterophic  Prokaryotes include photosynthetic, chemosynthetic and heterotopic species, making them the most tropically diverse in the biosphere.  Rhodopsins are light-absorbing pigments found in animal eyes and in the bacteria and archea; it provides many functions such as proton pump involved in the ATP synthesis. Photosynthesis  Infrared radiation is very important for temperature regulation by organisms.  Visible light is referred to as photosynthetically active radiation or PAR  PAR makes up 45% of the total energy content of the solar spectrum at sea level  Ecologist quantify PAR as photon flux density (PFD) Alternative photosynthetic pathways  During photosynthesis, the photosynthetic pigments of plants, algae, and bacteria absorb light and transfer their energy to electrons.  CAM (crassulacean acid metabolism) photosynthesis is largely limited to succulent plants in arid and semiarid environments. ENVS 1500 Chemical composition and nutrient requirements  The chemical composition is nearly similar with just carbon, oxygen, hydrogen, nitrogen and phosphorus.  Plants are the most chemically distinct  Plants obtain different essential nutrients through different organs Heterotrophs  Use organic molecules both as a source of carbon and as an energy source.  They depend ultimately on the carbon and energy fixed by autotrophs  3 Types of consumers 1. Carnivores 2. Herbivores 3. Detrivories  Herbivores, organism that eat living plants  Carnivores, organisms that mainly eat animals  Detrivories, organisms that feed on non-organic matter Detrivories  Example insects, fungi and bacteria  Control the movement of energy and nutrients in most ecosystems  Dominate food source is dead plants and plant parts  Face 3 main problems related to feeding 1. The search 2. The handling 3. The quality  Size affects species ability to find and handle food  Often classified by size  The abundance of food is not limiting Herbivores  Faced with a variety of physical and chemical defenses that make plants more difficult to eat, less nutritious and potentially lethal  The size of the food an herbivore eats is usually related to their size.  Herbivores must overcome a variety of chemical and physical defenses presented by plants before they are able to derive nutrition from a vegetarian diet Carnivores  Consume prey that are nutritionally rich and with a chemical compositions as themselves  Use size selective predation ENVS 1500 Chapter 4 Notes (pg. 103-104) Speciation  Physical and ecological processes interact with selection and drift to produce new species  Natural selection and genetic drift are two mechanisms that can cause dramatic changes in gene frequencies with in a population. What is Specie?  Biological species concept was presented by Ernst may in 1942  He defied species as “groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups”  Based on real ecological concept: reproductive isolation  Ecoline is a gradual change in genotype and / or phenotype of a species over a large geographic area  Ecotypes are a genetically identifiable subclass of a species that has evolved in response to local environment conditions  Biological species concept defines species upon revolutionary history and phylogenetic similarity ENVS 1500 Chapter 10 Notes (pg. 255-265, 271-277)  Population is defined as a group of potentially interbreeding individuals of a single species inhabiting a specific area  Many attributes of population are determined by interactions between the physiological ecology of species and the biotic and abiotic conditions that individuals encounter  All populations share several characteristics 1. Distribution 2. Number of individuals within and their density  Absolute density is the number of individuals of a population per unit area Distribution limits  The physical environment limits the geographic distribution of species Distribution patterns  On small scales individuals within populations are disturbed in patterns that may be random, regular or dumped on larger scales, individuals within a population are dumped.  Small scale refers to distances of no more than a few hundred meter, over which there is little environmental change significant to the organism under study  Large scale refers to areas over which there is sustainable environmental change.  A random distribution is one in which individuals within a population have a equal chance of living anywhere within a area  A regular distribution s on in which individuals are uniformly spaced  In a clumped distribution, individuals have much higher probability of being found in some areas then in others  3 basic patterns of distribution 1. Structures of the physical environment 2. Combinations of interactions 3. Environmental structure Commonness and rarity  Commonness and rarity of species are influenced by population, size, geographic range and habitat tolerance  Deborah Rabinowitz devised a classification of commonness and rarity, based on combinations of three factors 1. The geographic range of a species (extensive vs. restricted) 2. Habitat tolerance (broad vs. narrow) 3. Local population size (large vs. small) ENVS 1500 Lecture 3 Readings Chapter 2 Notes (pg. 13-49)  Natural history is the study of how organisms in a particular area are influenced by factors such as climate, soils, predators, competitors, mutualists, and evolutionary history  A solid understanding of natural history provides the foundation for modern ecology and conservation biology  Biomes are distinguished primarily by the commonly observed plant species and each is associated with a particular climate. Each biomes natural history differs a great deal. Section 2.1  Uneven heating of the earth’s physical surface by the sun and the tilt of the earth on its axis combine to produce predictable latitudinal variation in climate.  Several attributes of climate vary predictably over the earth. For instance, average temperatures are lower and more seasonal and at middle and high latitudes than near the equator  Much of earth’s climate variation is caused by uneven heating of its surface by the sun. This uneven heating results from spherical shape of the earth and the angle it rotates on its axis as it orbits the sun  Climate diagrams were developed by Heinrich Walter (1985) as a tool to explore the relationship between the distribution of terrestrial vegetation and climate  Climate diagrams summarize a great deal of useful climatic information Section 2.2  Soil structure results from long term interaction of climate, organisms, topography and parent mineral material  Soil is a complex mixture of living and non-living material upon which most terrestrial life depends, it’s important in sustaining the communities and ecosystems, they are complex ecological systems.  In Canada, this organic horizon will be called either the O horizon or the LFH horizon  O horizons are found in soils which the plant material is primarily aquatic in soils which the plant material is primarily aquatic in nature (e.g. peat mosses)  LFH horizons are generally found in more upland areas  The A horizon contains a mixture of mineral materials such as clay, slit and sand  The B horizon contains the materials leeched from above  The C horizon consists of weathered parent material  Soil is a complex & dynamic entity, it forms the medium in which organisms grow and the activities of those organisms in turn affect soil structure ENVS 1500 Section 2.3  The geographic disturbtion of terrestrial biomes corresponds closely to variation in climate, especially prevailing temperatures and precipitation.  Scientist came up with the realization that that not only can plants respond to climatic change they can influence climate themselves  Dividing the world into biomes is a very subjective process and biomes are not truly distinctive entities  Earths major biomes o Tundra o Desert o Boreal forest o Tropical savanna o Mediterranean woodland and shrub land o Temperate forest o Tropical dry forest o Temperate grassland o Tropical rain forest o Ice/snow dominated ENVS 1500 Chapter 3 Notes (pg. 51-80)  Cultures everywhere have a land-centered perspective on what our earth is Section 3.1  Over 71% of the earths surface is covered in water, this water is evenly disturbed among aquatic environments such as lakes, rivers and oceans.  The oceans contain over 97% of the water in the biosphere  The polar icecaps and glaciers contain an additional 2%  Less than 1% is freshwater in rivers and lakes and actively exchanged groundwater  Nearly 20% of the planets fresh water is found in Canada even though Canada only contains 7% of the world’s landmass  Across the world over 65% of fresh water is found In glaciers and ice fields, and nearly 30% is ground water  Because of changes to freshwater supplies and demands the disturbtion of water across the biosphere is dynamic  Various aquatic environments such as lakes, rivers and oceans plus the atmosphere, ice and even organisms can be considered as “reservoirs” within the hydrologic cycle  The hydrologic cycle is powered by solar energy which drives the winds and evaporates water Section 3.2  The biology of aquatic environments corresponds broadly to variations in physical factors such as light, temperature, and water movements to chemical factors such as salinity and oxygen  All organisms that undergo oxidative respiration require a reliable source of oxygen  In water, oxygen is dissolved  All organisms contain substantial amount of water along with a number of minerals  Oceans are the largest aquatic environment in the world  Examples of aquatic environments: o Oceans o Kelp forests and coral refs o Intertidal zones o Rivers and streams o Salt marshes and mangrove forests o Lakes and ponds o Bogs and fens ENVS 1500 Lecture 4 Readings Chapter 4 Notes (pg. 89-98, 100-110)  The great diversity of organisms that live on the planet and the even greater diversity of organisms that have gone extinct are all a product of evolution and speciation  Ecology and evolution are linked and neither would occur without the other  Ecological interaction are the mechanisms that allow evolution by natural selection  Darwin’s theory of evolution by natural selection is a unifying concept of modern biology. It was crystalized by his observations in the Galapagos islands  Evolution, a process that changes populations of organisms over time  Survival of the fitness, the individuals with favorable characteristics would have a greater chance of surviving  The theory of natural selection: 1. More offspring are produced each generation that can be supported by the environment 2. There is variation in physical, physiological, and behavioral traits among individuals in a population. Some of this variation is heritable (passed on to offspring) 3. Some traits will give some individuals an advantage over others. Individual =s who posses those traits will have a higher chance of surviving and reproducing than the other members of the population, increasing their fitness 4. Traits that result in increased fitness will become more common within a population over subsequent generations.  Darwin proposed that differential survival and reproduction of individuals would produce changes in species populations that increase the fitness of individuals within the environment  Evolution can lead to adaptations, adaptations are not something that an individual evolves out of need or desire, rater it is a trait that has been selected through natural selection  Mendelian genetics include the fundamental concept of particulate inheritance; this concept passes from parent to offspring in the form of genes.  Mendel also determined that genes come in alternative forms called alleles.  Also found out about dominate and recessive alleles Section 4.1  Phenotypic variation among individuals in a population results from the combined effects of genes and environment  Natural selection cannot occur unless there is phenotypic variation among individuals  Evolution by natural selection depends upon the heritability of traits. ENVS 1500  Heritability in a broad sense is the proportion of total phenotypic variation in a trait Section 4.2  Changes in gene frequency within a population can occur through both natural selection and random processes such as genetic drift  One form of natural selection is called stabilizing selection. Acts to impede directional changes in the population  Directional selection favors an extreme phenotype over other phenotypes in the population  Disruptive selection favors to or more extreme phenotypes over the average phenotype in a population  A founder effect can be defined as a decrease in a genetic diversity associated with the formation of a new, small population Section 4.3  Physical and ecological process interact with selection and drift to produce new species  Natural selection and genetic drift are two mechanism that can cause dramatic changes in gene frequencies within a population  Biological species concept: “ groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups”  An Ecoline is a gradual change in genotype and/or phenotype of a species over a large geographic area  Ecotypes is a genetically identifiable subclass of a species that evolved in response to local environmental conditions  Speciation occurs when a single population becomes spatially subdivided into multiple subpopulations  Parapatric speciation occurs when a population expands into a new habitat within the pre existing range of the parent species  In sympatric speciation a single parent population forms genetically distinct subpopulations without any geographic barrier or spatial isolation  Parallel evolution when species in similar habitats but geographically isolated evolve similar traits ENVS 1500 Lecture 5 Readings Chapter 4 Notes (pg. 89-98, 100-110)  The great diversity of organisms that live on the planet and the even greater diversity of organisms that have gone extinct are all a product of evolution and speciation  Ecology and evolution are linked and neither would occur without the other  Ecological interaction are the mechanisms that allow evolution by natural selection  Darwin’s theory of evolution by natural selection is a unifying concept of modern biology. It was crystalized by his observations in the Galapagos islands  Evolution, a process that changes populations of organisms over time  Survival of the fitness, the individuals with favorable characteristics would have a greater chance of surviving  The theory of natural selection: 5. More offspring are produced each generation that can be supported by the environment 6. There is variation in physical, physiological, and behavioral traits among individuals in a population. Some of this variation is heritable (passed on to offspring) 7. Some traits will give some individuals an advantage over others. Individual =s who posses those traits will have a higher chance of surviving and reproducing than the other members of the population, increasing their fitness 8. Traits that result in increased fitness will become more common within a population over subsequent generations.  Darwin proposed that differential survival and reproduction of individuals would produce changes in species populations that increase the fitness of individuals within the environment  Evolution can lead to adaptations, adaptations are not something that an individual evolves out of need or desire, rater it is a trait that has been selected through natural selection  Mendelian genetics include the fundamental concept of particulate inheritance; this concept passes from parent to offspring in the form of genes.  Mendel also determined that genes come in alternative forms called alleles.  Also found out about dominate and recessive alleles Section 4.1  Phenotypic variation among individuals in a population results from the combined effects of genes and environment  Natural selection cannot occur unless there is phenotypic variation among individuals  Evolution by natural selection depends upon the heritability of traits. ENVS 1500  Heritability in a broad sense is the proportion of total phenotypic variation in a trait Section 4.2  Changes in gene frequency within a population can occur through both natural selection and random processes such as genetic drift  One form of natural selection is called stabilizing selection. Acts to impede directional changes in the population  Directional selection favors an extreme phenotype over other phenotypes in the population  Disruptive selection favors to or more extreme phenotypes over the average phenotype in a population  A founder effect can be defined as a decrease in a genetic diversity associated with the formation of a new, small population Section 4.3  Physical and ecological process interact with selection and drift to produce new species  Natural selection and genetic drift are two mechanism that can cause dramatic changes in gene frequencies within a population  Biological species concept: “ groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups”  An Ecoline is a gradual change in genotype and/or phenotype of a species over a large geographic area  Ecotypes is a genetically identifiable subclass of a species that evolved in response to local environmental conditions  Speciation occurs when a single population becomes spatially subdivided into multiple subpopulations  Parapatric speciation occurs when a population expands into a new habitat within the pre existing range of the parent species  In sympatric speciation a single parent population forms genetically distinct subpopulations without any geographic barrier or spatial isolation  Parallel evolution when species in similar habitats but geographically isolated evolve similar traits ENVS 1500 Chapter 11 Notes (Pg. 282-293)  Population structures can be defined by a number of factors 1. Patterns of mortality 2. Age disturbtion 3. Sex ratios 4. Dispersal Section 11.1  A survivorship curve summarizes the pattern of survival in a population  One of the most fundamental descriptions of a population is the pattern of morality and survival among individuals  Patterns of survival vary regarding species and environmental circumstances  In response to practical changes of discerning patterns of survival ecologists invented a bookkeeping device called life tables that lists births, the survivorship, and the deaths or mortality in populations  There are 3 ways of estimating patterns of survival within a population 1. Identify a large number of individuals that are born at about the same time and keep record on them from birth to death. A group born at the same time is called a cohort; a life table made from data collected this what is called a cohort life table. 2. To record the age at death of a large number of individuals. This method produces a static life table 3. From the age disturbtion, done by calculating the difference in proportion  A survivorship curve shows patterns of life and death within a population. It lets us quickly determine whether morality rates for a given population change with age  A relatively high rate of survival among young and middle aged individuals followed by a high rate of morality among the aged is known as type I leadership curve.  Constant rates of survival known as a type II survivorship curve.  A type III survivorship curve is one in which a period of extremely high rates of morality among the young is followed by a relatively high rate of survival.  Survivorships can be thought as “Coles notes” od understanding patterns of morality in natural populations they do not include all the fine details found in nature but instead serve as useless summaries of survival patterns within populations Section 11.2  The age disturbtion of a population reflects its history of survival, reproduction and potential for future growth.  A lot can be told about a population by its age disturbtion  By studying the history of a population through describing its age disturbtion population ecologists can make predictions about its future ENVS 1500 Section 11.3  Population sex rations can change depending upon the relative fitness of different sexes within a population.  By studying patterns of morality and age disturbtion, ecologists are able to understand many process that are occurring within populations  Sex ratios an be defined as the relative frequency of each sex type in a population  Frequency dependent selection is where the relative fitness of producing ales or females is not inherent in the gender of the offspring itself instead is dependent upon the relative frequency of both alternative phenotypes Section 11.4  Dispersal can increase or decrease population density  The seeds of plant disperse with wind, water and even animals  Migration is the seasonal movement of individuals from one location to another while dispersal is a permanent exodus from one population into another ENVS 1500 Lecture 6 Readings Chapter 12 Notes (pg. 305-309, 311-327) Section 12.1  Population size changes as a function of birth rates, death rates, immigration, and emigration.  There are four factors that can cause a population to change in size 1. Births of new individuals 2. Immigration into the population 3. Deaths 4. Emigration out of the population  In animal species, births are usually counted as the number of eggs laid  In plant species, births are usually counted by seeds  In bacteria, the birth rate is measured as the rate of cell division  As a group the number of births, immigrants, deaths, and emigrants in a population are described as the BIDE dynamics and they explain changes in size of all populations on this planet and likely any others. This can be seen by constructing a simple equation: Nt+1 = Nt + B + I – D – E o Nt is the size of the population at some earlier time o The time interval +1 maybe one year, day, hour, or second depending on the biology of the organism of interest and the personal preference of the ecologist o B, I, D, E represents the number of individuals that were born, immigrated, died or emigrated over this time interval o Very simple and a useful accounting exercise to determine whether population size is changing over time, complexity arises when we want to compare differences among populations or understand why changes are occurring. o The first step to making these comparisons is to recognize the differences between per-capita rates of birth death immigration and emigration  Biotic factors are typically referred to as density- dependent factors  Abiotic factors are referred to density-independent factors Section 12.2  In a population with stable age disturbtion, the proportion of individuals in each of the age classes is constant  The geometric rate of increase is the ratio of the population size at two points Section 12.3  In the presence of abundant recourses populations can grow at geometric or exponential rates  A population growing at its maximum rate will add a few new individuals at first and then increasingly more at each later step in time ENVS 1500  Growth by any population can be modeled as geometric population growth in which successive generations differ in sixe by a constant ratio  Continuous population growth in an unlimited environment can be modeled as exponential population growth Section 12.4  If resources become limited, population growth rate slows and eventually stops; this is known as logistic population growth  Exponential growth cannot continue indefinitely  Resource limitations, competitors, predators, pathogens, and other factors all act to reduce the rate of population  The populations size at which growth stops is generally called the carrying capacity ENVS 1500 Chapter 9 Notes  The combination of suitable conditions is a specie’s niche Section 9.1  Because all organisms have access to limited energy and resources there are fundamental trade offs in how these can be allocated between survival offspring number and offspring size  If seeds had hooks, spines or bars they were classified as adhesion-adapted  The structure of some seeds generally containing oil attractive to ants as any- dispersed are called elaiosome  Vertebrate - dispersed are seeds containing a flesh or aril, a fleshy covering of some seeds that attract birds and other vertebrates  Scatter hoarded are seeds known to be gathered by mammals and stored in scattered caches or hoards  Plant growth forms associated with different size seeds  Reproductive effort is the allocation of energy, time and other resources to the production and care of offspring. Section 9.2  The great diversity of life historians observed in nature can be classified on the basis of a few common characteristics Section 9.3  The fundamental niche reflects the environmental requirements of species, while the realized niche also includes interactions with other species  Most adaptions require energy  Basic meaning of niche was that of a recessed place in a wall where one can set up or display items  To ecologist the niche summarizes the factors that influence the growth, survival and reproduction of species  The niche concept was developed by Joseph Grinnell and Charles Elton  The fundamental niche defines the physical conditions under which a species might live in the absence of interactions with other species  Interactions among species such as competition may restrict the environments in which species can actually persist is called realized niche  Allopolyploid is a process of speciation initiated by hydration of two different species ENVS 1500 Lecture 7 Readings Chapter 9 Notes (pg. 243-245) Section 9.3  The fundamental niche reflects the environmental requirements of species, while the realized niche also includes interactions with other species  Most adaptions require energy  Basic meaning of niche was that of a recessed place in a wall where one can set up or display items  To ecologist the niche summarizes the factors that influence the growth, survival and reproduction of species  The niche concept was developed by Joseph Grinnell and Charles Elton  The fundamental niche defines the physical conditions under which a species might live in the absence of interactions with other species  Interactions among species such as competition may restrict the environments in which species can actually persist is called realized niche  Allopolyploid is a process of speciation initiated by hydration of two different species ENVS 1500 Chapter 13 Notes (pg. 328-335, 340-349) Section 13.1  Individuals can compete with other individuals, of their own and of different species, in a number of different ways.  Interference competition involves direct aggressive interactions between individuals  Intraspecific competition is completion within the same type of species  Interspecific completion is competition between different species  The effects on competition on the fitness of the competitor’s are not necessarily the same for all the individuals of different species Section 13.2  Field and microcosm studies show that resource limitations and competitions are widespread Section 13.3  The competitive exclusion principle states that “complete competitors cannot coexist” Section 13.4  Competition can have significant effects on species coexistence and the direction of evolution.  Character displacement is the idea that two species that live apart ma be nearly identical in form and function though when the species live together competition will cause the evolution of some meaningful differences between them ENVS 1500 Lecture 8 Readings Chapter 14 Notes (pg. 354-368, 371-372,378-381)  Some of the strongest ecological interactions in natural systems are based upon exploitation of one organism by another  Predators do more then hunt their prey, when they are unsuccessful they are still have some sort of control on their prey. For example they may change that species behavior increasing stress hormones and having significant consequences when the prey escapes the chase.  Parasitic interactions are considered exploitative, and so is mutualism a related form  In exploitative relationships one participant exploits another where in competition all the participants exploit a share of resources  Predators kill and consume other organisms  Exploitation is at the expense of another Section 14.1  Herbivory is a widespread ecological interaction and has caused the evaluation of a diversity of plant strategies Section 14.2  Prey populations are influenced by food availability by being consumed by predators and through non-consumptive effects of predators  Animals affect their food supply  Direct consumptive effects of predation influence only a small number of prey at any particular point in time  Predators do more then kill, there is evidence that nonconsumptive effects of predation also have significant on pry population dynamics Section 14.3  The population consequences of exploitative relationships can be explored with theoretical models Section 14.4  Prey populations can persist in the presence of predators through the use of refugia and a diversity of defense strategies  Most animals are masters of disguise  An example is camouflage  Some species are poisonous and advertise it throughout color usually bright this is called aposematic coloration  Batesian mimicry is when a harmless specie mimics a harmless one  Mullerian mimicry is also common ENVS 1500 Chapter 15 Notes (pg. 384-390,396-400)  Symbiotic relationships are when the organisms live in close proximity to each other where in a non symbiotic relationship the organisms live far from each other  Mutualism is interactions between individuals of different species that have a net benefit of both partners. There are two types o Facultative mutualism: Where the organisms can live without each other o Obligate mutualism: Where species are heavily dependent on each other Section 15.1  There is great diversity in the types of parasitic and mutualistic interactions that exist, defying easy generalization  Parasites usually alter the behavior of the host in ways that would benefit the transmission  3 different types of interactions 1. Predation 2. Parasitism 3. Competition Section 15.3  Many interactions an switch from parasitic to mutualistic depending upon the specific conditions of the local environment  Nectar robbers exploit energy full resources ENVS 1500 Lecture 9 Readings Chapter 16 Notes (pg. 414-421,423-433)  A community is an association of interacting species inhabiting some defined areas  Community structures includes attributes such as the number of species the relative abundance of species and the kinds of species compromising a community  A guild is a group of organisms that all make their living in a similar way Section 16.1  Most species are moderately abundant; few are very abundant or extremely rare.  A specie is dominant when it substantially more common than the other species in the community Section 16.2  A combination of the number of species and their relative abundance define species diversity  Variation in species found in a community is referred to as species diversity  The number of species in a community is called species evenness  Dominance is referred to as species richness  Rank abundance curve provides us with important information about a community Section 16.3  Species diversity is higher in complex environments Section 16.4  Intermediate levels of disturbance promote higher diversity  Equilibrium shows where stability is maintained ENVS 1500 Chapter 17 Notes (pg. 435-454) Section 17.1  A food web summarizes the feeding relations in a community Section 17.2  Strong competitors can alter community structure  Competitive hierarchies were established in some communities Section 17.3  The activities of a few keysto
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