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Transcript
Chapter 6 Community Ecology, Population Ecology, & Sustainability Community Structure • Structure of a community (populations of all species living and interacting in an area at a particular time) – Physical appearance: relative size, stratification & species distribution – Species diversity: # of different species – Species abundance: # of individuals of each species – Niche structure: number of niches, how they differ & how they interact Physical Appearance • Differences in physical structure and properties create transition zones between 2 ecosystems (ecotones) – Edge effect: area between forest and grasslands – Many animals and plants thrive “on the edge” – Many species can become stressed in the edge as well Species Diversity & Abundance • Most of the Earth’s diversity is in the rainforest, coral reefs, deep sea & large tropical lakes • Large amount of diversity = low number of organisms of a particular type (abundance) • Three major factors effect diversity – Latitude in terrestrial communities – Depth in aquatic zones – Pollution in aquatic communities Niche Structure • Niche is analogous to its job • Ecological niche represents the adaptations or adaptive traits through evolution • Fundamental niche: full potential range if there is no competition for resources • Realized niche: occupies only part of its fundamental niche – Generalist species have broad niches – Specialized species have narrow niches Types of Species • Native – normally live in an ecosystem • Non-native – (invasive or exotic) deliberately or accidentally introduced into an ecosystem • Indicator – serve as early warning signs for damage or pollution of an ecosystem • Keystone – play a critical ecological role by effecting the type and abundance of other species • Foundation – enhance a habitat to benefit other species Species Interaction • Interspecific competition– competition between species for food & resources – Resource partitioning – adapt to reduce competition (hawks & owls) • Predation – one species (predator/hunter) lives off of another species (prey/hunted) • Parasitism – one species (parasite) lives on another species (host) • Mutualism – two species live together to benefit both • Commensalism – one species benefits, but the other is not harmed Ecological Succession • All communities and ecosystems change constantly • Ecological succession – gradual change in species composition – Primary succession: biotic communities in an abiotic environment – Secondary succession: biotic communities in an biotic environment Primary Succession • See figure 6-9 on page 119. • Begins in a lifeless area where there is no soil or bottom sediment (bare rocks, parking lots, cooled lava, etc. • Lichens & mosses build up soils • Early successional plant species (herbs & grasses) grow fast & have short lives • Mid-successional plant species (shrubs & trees) • Late successional plant species (trees that can tolerate shade) becomes a complex forest community Secondary Succession • See figure 6-10 on page 120. • Begins in an area that has soil and was previously a community of organisms • New vegetation can grow due to winds carrying seeds, or animal droppings • Secondary succession includes – – – – Abandoned cropland Burned or cut forests Heavily polluted streams, ponds or lakes Land that has been dammed or flooded Disturbances • Changes in the environment that disrupts the ecosystem – Catastrophic or mild – Natural or caused by humans – Detrimental or beneficial • Intermediate disturbance hypothesis predicts that communities that experience frequent but moderate disturbances have the most species diversity The Balance of Nature? • Climax community: dominated by few long-lived plant species and is at equilibrium • Ever-changing mosaic vegetation patches at different stages of succession • We can not predict the course of succession toward an ideal climax community Population Change • Four variables – – – – Birth Death Immigration Emigration • Population change = (birth + immigration) – (deaths + emigration) Limits on Population Growth • Biotic potential – capacity for growth • Intrinsic rate of increase (r) – rate of growth if there were unlimited resources • Environmental resistance – all factors that act together to limit growth • Carrying capacity (K) – the result of biotic potential and environmental resistance • Minimum Viable Population (MVP) – certain minimum population required to sustain its growth Exponential vs Logistic • Exponential growth starts small increasing ever so rapidly (J shaped) • Logistic growth starts slow, increases for a time and then levels off (S shaped) – Overshoot – an initial spike followed by a decline in population (reproduction time log) – Carrying capacity – population becomes a constant (at equilibrium) Predation In Population Control • Top-down control: predator periodically reduces the population of prey, which then reduces the population of the predator, which in turn allows the prey population to increase again • Bottom-up control: periodic population crashes influence the food supply Reproduction & Survival • Asexual reproduction – clones of their parents • Sexual reproduction – requires genetic information from 2 parents – Provides greater genetic diversity – Allows the males to gather food & help raise the young Reproductive Patterns • K-selected species are competitors – Many offspring each time they reproduce – Early reproductive rate – High potential growth rate • R-selected species are opportunists – – – – Born live, mature slowly & cared for by parent Do well in competitive situations Low reproductive rates Thrive best in constant environments Human Impacts on Ecosystems • Reduced biodiversity by destroying, fragmenting, degrading & simplifying wildlife habitats • Used, wasted, and destroyed an increasing percentage of Earth’s net primary productivity • Strengthened some populations of pests and disease causing bacteria and viruses • Eliminated some predators • Deliberately or accidentally introduced non-native species into communities Human Impacts (cont.) • Used some renewable resources faster than we can replenish • Interfere with the normal chemical cycling and energy flows in ecosystems • Become increasingly dependent on nonrenewable energy sources – fossil fuels – which have a whole host of global impacts in the extraction, processing, consumption and disposal of waste product generated by the use of fossil fuels Ecosystem Stability • Stability is maintained by constant dynamic change – Inertia (persistence) is the ability for organisms to resist change – Consistency is a restriction to change due to limited resources – Resiliency is the ability for organisms to bounce back Sustainability • • • • • • Human aspects can be controlled Balance of resource usage Use less and waste less Alternatives must be utilized “Going Green” Strive for sustainable communities Sustainability • Lifestyles – we need to change • Connections – we need to be aware of our interdependency with everything else • Intrusion – we need to ask ourselves what happens when we alter nature • Can not continue to deplete & degrade – we need to become more sustainable in all aspects of our lives The Precautionary Principle • It is important to take precaution in activities or behavior that may be harmful to the health of species or the environment. • See figure 6-18 on page 126.