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Geographical Biogeosciences
GEOB 102
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ORGANISMS AND THE ENVIRONMENT (Ch 21 – Biogeographic Processes) I. ENVIRONMENTAL FACTORS A. Resources - all things consumed by an organism - consumption causes a decrease in supply of resources (less is available) - plants need: 1. 2. 3. 4. 5. - animals need: 1. 2. 3. 4. B. Environmental Factors - abiotic environmental factors that influence organisms but are not consumed 1. Climatic a. Temperature - directly influences rates of physiological processes - metabolic processes have a certain temperature range - influences animal physiology and need for shelter - ectotherms - endotherms - indirectly influences the availability of/demand on resources b. Light - Photoperiod = seasonal changes in light that trigger life processes - plants - animals c. Wind - vegetation structure in exposed locations 2. Edaphic Factors = soil - texture, structure, organic matter, organisms, acidity and alkalinity 3. Geomorphic Factors = landforms - slope steepness = angle relative to horizontal - slope aspect = orientation of the slope - relief or slope position II. ENVIRONMENTAL FACTORS AND SPECIES DISTRIBUTION A. Theory of Tolerance - each and every species is able to exist and reproduce successfully only within a definite range of values for a particular environmental factor R = organisms grow and Reproduce successfully G = organisms Grow but cannot reproduce S = organisms Survive or persist but cannot grow T = Tolerance range for that factor, beyond tolerance is lethal O = Optimum level, at that level maximum performance Note: there are both upper and lower limits of tolerance, beyond which the organism dies B. Bioclimatic Frontiers - climate factors interacting to determine the distributional limit of a species - what climatic elements limit: (a) ponderosa pine? (b) sugar maple? C. Ecological Niche - Total structural and functional role of a species in the ecosystem - characteristics of a species niche include combined tolerance ranges for all the environmental factors that influence the species - each factor can be considered as one niche dimension - multidimensional - as many dimensions as factors that define the niche - factors also include biotic interactions: 1. Negative interactions (cost to one or both species) 2. Positive interactions (benefit one or both species) D. Niche versus Habitat Niche - role of a species, "profession" - Fundamental niche = potential distribution of the species with optimal conditions (no competition) - Realized niche = actual habitats where organism is found due to interactions and limitations on resources – presence of competition. Habitat - the actual place where the organisms lives, "address" - characterized by a particular set of environmental factors that match the organisms niche. POPULATION February-25-13 10:05 AM  Population - a group of organisms of the same species in a given place at the same time  Population Dynamics - changes may occur between locations (spatial) - changes in the number of individuals within a population (temporal) A. Spatial Distribution Recall from last class, Habitat = area with particular set of environmental factors (abiotic and biotic) that match the organism’s niche.  Range: space of distribution. Does not grow on top of the mountain.  Dispersal: ability to move from birth site to a new (another) site. 1. Ecological dispersal: occurs within a geographic range -movement of a 'propagule' that can establish a new individual. -examples: pollination (plants), eaten by animals (birds or flying insects), pieces of plants. 2. Geographical dispersal: expansion of the range 3. jump dispersal: cattle egret = jump dispersal followed by diffusion in the Americas. Reproduction and finding new habitat (diffuse). 4. Diffusion: looking for new habitat and settling in. Corridors = regions of similar climate and vegetation structure that facilitate dispersal (ex: restoring and managing habitat for reptile and amphibians. US Natural Resources Conservation Services).  Corridors = regions of similar climate and vegetation structure that facilitate dispersal  Barriers = regions a species is unable to colonize, inhibit dispersal - ecological barriers: biotic interactions (hint think about biotic interactions). Examples are cattle egret in the savannah. - geographic barriers: physical barriers (see allopatric speciation, next lecture). Examples are man-made. A. Temporal Change: Population Growth Models Simple Model of Population Growth - consider a population - how many ways can it change in size (individuals become more or less abundant)? 1. births 2. immigration 3. deaths 4. emigration - populations change in size due to interactions of individual organisms with the environment  Geometric Growth versus Logistic Growth  Geometric Growth e.g. Duckweed (Lemna minor) -smallest flowering plant -reproduces from seed or vegetatively (asexually) abundance time Example of Population Crash e.g Kaibab deer in Arizona  Logistic Growth - in nature, populations increase to a relatively constant abundance according to the logistic population growth model K = carrying capacity = number of individuals of a species that can be supported relatively continuously in a given environment - as environmental factors fluctuate with time, the actual number of individuals in the population also varies around K. EVOLUTION: A POPULATION PROCESS February-27-13 9:59 AM GEOB102: BIOGEOGRAPHY 3 EVOLUTION: A POPULATION PROCESS A. Charles Darwin 1859: The Theory of Evolution What do scientists mean by "theory"? - in common use among non-scientists the term theory suggests that an idea remains unproven or even dubious: “it’s just a theory” - in science, theory is a large and important body of knowledge and explanatory concepts that seeks to increase our understanding of a major natural phenomenon - theory: a body of knowledge that is unlikely to be disproved, but is likely to be improved through testing hypotheses using the scientific method. B. Darwin’s Theory Rests on 6 Fundamental Propositions: 1. Individuals that make up populations vary. 2. At least some of the variation is heritable. Genes are the units passed from parents to offspring. 3. "The Struggle for Existence." All populations/species have biological potential to populate much larger areas/ranges, but they do not as resources are limited and other environmental conditions affect populations (not getting eaten before reproduce). 4. Different individuals possessing different traits leave different numbers of descendants. 5. "Survival of the Fittest" The number of descendants that an individual leaves depends largely on interactions of the individual (and its characteristics/traits) with the environment. 6. "Natural Selection." Individuals possessing genetically based traits that enhance their survival and reproduction in a particular environment will leave more offspring. The environment “selects” favourable traits. The population will change in genetic structure with environmental change.  Evolution: change in gene frequency in a population over time. Changes lead to differential survival and reproductive success of individuals and population evolve.  Adaptation by Natural Selection: genetically determined traits help individuals cope with their environment. Arises through evolution of reproduction.  “Survival of the Fittest”: successful reproduction by individuals best adapted to the environment ( those with best traits). Example of evolutionary processes: Peppered Moth CHANGE IN GENE FREQUENCY Lichen killed = dark trees Light moths = visible Dark moths = camouflage Light moths dispersed or were predated by birds Dark moths > light moths In-class assignment: Identify and briefly explain each of the six fundamental propositions of the theory of evolution for the peppered moth. 1. Yes vary by color 2. Yes: control for color, genetic makeup switches. 3. Not being eaten by the birds. 4. Color determines survival from predators. 5. Those better camouflaged contribute to reproductive success of individuals. 6. Genes that control (black color). C. Modern Genetics and Sources of Genetic Variation Mutation: change to genetic material (DNA) passed from parent to offspring Recombination: offspring receives two slightly different copies of each gene from its parents - number of possible genetic combinations is very large (can depend slightly on what kind of gene it is) - each individual is unique (change in morphology, physiology and behavior) Polyploidy: offspring receive two sets of genes from each parent - fertile, but cannot interbreed with original population = new species (genes stick together and come as double copies) D. Speciation Species: individuals capable of interbreeding to produce fertile offspring Genotype: an organism’s full hereditary information – the particular set of genes it possesses. Phenotype: actual, observed properties of an organism (morphology, development, behaviour), results from interaction of genes + environment. Speciation: set of processes by which species are differentiated and maintained: 1. Genetic variation 2. Natural selection: suitability of genes in the environment. 3. Genetic drift: random changes to the genetic composition of a breeding population leading to changes in gene frequency. Overtime can lead to new species.  Gene flow: opposite to speciation (constant mixing of genes tends to dilute variation and prevent differentiation. -reduces processes of speciation WAYS TO IMPROVE SPECIATION (DARIN'S FINCHES)...  Geographic isolation: facilitates speciation by isolating populations, preventing gene flow, accentuates genetic drift  Adaptive radiation: new environment(s) provide opportunity for new species adjusted to different habitat(s).  Allopatric speciation - evolution of a new species by geographic isolation (physical barrier) -Barriers: plate tectonics, oceans or lakes, mountain ranges and deserts.  Sympatric speciation Cichlid fish) - speciation within a population, no spatially isolation -reproductive isolation: timing of reproduction, mate choice and ability to use habitat or resources. BIODIVERSITY AND GLOBAL ENVIRONMENTAL CHANGE March-01-13 10:04 AM GEOB 102: BIOGEOGRAPHY 5 BIODIVERSITY AND GLOBAL ENVIRONMENTAL CHANGE BIODIVERSITY A. Definition- from the International Convention on Biodiversity The variability among living organisms from all sources and the ecological complexes of which they are a part. This includes diversity within species, between species, within communities, ecosystems and landscapes. (include diversity within species, between species and within communities). - How many species exist today? -1.75 million species known to western science - estimates of 4-30 million species -1million animals; 42,300 vertebrates, the remaining are invertebrates (75 % insects) -250,000 plants, most are flowering plants (90% flowering plants) - New species identified yearly - terrestrial invertebrates (e.g. insects), soil and subterranean organisms - freshwater and marine fish and other organisms (some still being discovered) B. Measuring Biodiversity 1. Species Composition - identify and name the species in a community (between habitat types and tropical regions) 2. Species Diversity - 2 major components a. species richness: number of species per unit area (e.g a count) b. species evenness: distribution of individuals among species = relative abundance (e.g a measure of equability) -Diversity indices: combine richness and evenness. e.g. Analysis of two gardens: Richness in both A and B is 5 Which garden is richer? Both are 5 Which garden is more even? B Which garden is more diverse? Community B C. Loss of Biodiversity Global Extinction = the fate of all species - loss of all individuals of a given species, genus, family or order over its entire range - unique genome is lost forever - ancestor becomes extinct as a new species evolves Local Extinction or Extirpation - species is lost from one or more geographic areas but persists elsewhere Rates of Extinction - over geologic time, more species have evolved and gone extinct than exist today -background rate = continuous extinction through geologic time - mass extinctions = periods of tremendous loss of biodiversity - 6 mass extinctions in the geologic record - 7th mass extinction = ongoing human impacts on global biodiversity Primary causes of extinction today: a. over-consumption by humans (over-harvesting, over hunting) b. introduction of exotic invasive species c. secondary losses when biotic interactions are jeopardized d. loss of habitat e.g. cumulative effects of re
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