CHAPTER 8.docx

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Western University
Environmental Science
Environmental Science 1021F/G
Geoff Stewart

CHAPTER 8: COMMUNITY ECOLOGY -5% of the Acadian forest remains in its natural state ALL THE PIECES OF THE ECOLOGICAL COMMUNITY PUZZLE ARE CONNECTED -50% of Maritimes land was covered in Acadian forest -ECOSYSTEMS: all of the organisms in a given area plus the physical environment in which, and with which they interact -HABITAT: the physical environment in which, and with which, individuals of a particular species can be found -COMMUNITY ECOLOGY: the study of all the populations (plants, animals, and other species) living and interacting in an area -boreal forest covers more than half of the country -boreal forests are dominated by coniferous trees -INDICATOR SPECIES: the species that are particularly vulnerable to ecosystem perturbations, and that, when we monitor them, can give us advance warning of a problem (example: lichens) -if indicator species begin to disappear, this lets us know that there is a problem and gives us time to act before other species become affected MATTER AND ENERGY MOVE THROUGH A COMMUNITY VIA THE FOOD WEB -FOOD CHAIN: a simple, linear path starting with a plant (or other photosynthetic organism) that identifies what each organisms in the path eats -food chains linked together makes the food web -FOOD WEB: a linkage of all the food chains together that shows the many connections in the community -CONSUMER: an organism that eats other organisms to gain energy and nutrients; includes animals, fungi, and most bacteria -consumers eat producers -PRODUCER: a photosynthetic organism that captures solar energy directly and uses it to produce its own food (sugar) -PRIMARY CONSUMERS EAT PRODUCERS -SECONDARY CONSUMERS EAT PRIMARY CONSUMERS -TERTIARY CONSUMESR EAT SECONDARY CONSUMERS -at the top of the food chain is the APEX PREDATORS, they are in the last trophic level -TROPHIC LEVELS: feeding levels in a food chain -when any of these organisms die, they are eaten by a consumer called a detritivore and decomposers -DETRITIVORES: consumers (including worms, insects, crabs, etc) who eat dear organic material -DECOMPOSERS: organisms such as bacteria and fungi that break organic matter all the way down to constituent atoms or molecules in a form that plants can take back up -as one moves up the food chain, energy and biomass (all the organisms at that level) decrease, creating a trophic pyramid -an organism only passes 10% of the energy onto the predator consuming it -a pyramid’s ultimate size is determined by the size of its first trophic level, which is the one made up of photosynthesizing producers (usually plants) -productivity – the amount of energy trapped by producers ad converted into organic molecules like sugar – is limited by sunlight and nutrient availability -GROSS PRIMARY PRODUCTIVITY: a measure of the total amount of energy captured via photosynthesis and transferred to organic molecules in an ecosystem -plants only use 50% of the energy they produce to fuel their daily needs -NET PRIMARY PRODUCTIVITY (NPP): a measure of the amount of energy captured via photosynthesis and stored in photosynthetic organisms -the net is a measure of energy available to higher trophic levels -anything that alters NPP can potentially affect organisms at every other level of the trophic pyramid THE ACADIAM FORECT IS SHAPED BY BIOTIC AND ABIOTIC FORCES -the connections among species, and between species and their environment, give rise to ecosystem complexity -ECOSYSTEM COMPLEXITY: a measure of the number of species at each trophic level, as well as the total number of trophic levels and available niches -each species occupy a specific niche -NICHE: the role of a species plays in its community, including how it gets its energy and nutrients, what habitat requirements it has, and what other species and parts of the ecosystem it interacts with -greater ecosystem complexity means more niches and thus more ways for matter and energy to be accessed and exchanged -RESILIENCE: the ability of an ecosystem to recover when it is damaged or perturbed -SPECIES DIVERSITY, which refers to the variety of species in an area, is measured in two different ways: species richness and species evenness -SPECIES RICHNESS: the total number of different species in a community -SPECIES EVENNESS: the relative abundance of each species in a community -populations of organisms at a higher trophic level will have fewer members than those at a lower trophic level – but populations of organisms within the same trophic level often have similar numbers – if they do then the community is said to have high species evenness – if they don’t and one species dominates at a given trophic level then that community is said to have low species evenness -higher species richness and evenness make for a more complex community and a more intricate food web – which enables more matter and energy to be brought into the system and also makes the community less likely to collapse in the face of calamity -ECOTONES: regions of distinctly different physical areas that serve as boundaries beyween different communities -EDGE EFFECTS: the different physical make up of the ecotone that creates different conditions that either attract or repel certain species (for instance, it is drier, warmer and more open at the edge of a forest and field that it is further in the fore
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