Lecture 11 - 2/17/2011 Announcements Introduction to...

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Unformatted text preview: 2/17/2011 Announcements Introduction to Ecosystems No classes next week – Reading Week Midterms will be returned in tutorial #3 Final Exam: Tuesday April 26, 2-5pm 2 A-Sc: EX200 EX200 Se – Z: EX100 ENV200H1S – February 17 2011 1 An overview on ecosystems: 2 Ecosystems What are they? What are their important characteristics? How are they organized? Keystone species Interaction of many organisms functioning together through physical and chemical environments We can generally recognize when we have moved across the boundary separating one ecosystem from another (lake-beach or forest-meadow), but (lakeforestthere there will be a larger or smaller intermediate zone between between two systems – the ecotone. ecotone. We can group ecosystems from a particular region into landscapes (or biomes) – a concept that works biomes) somewhat better for terrestrial than for aquatic systems Natural ecosystems persist without external subsidies of energy, water or nutrients (self(selfsustaining). sustaining). 3 Basic Characteristics of Ecosystems Structure non living: physical-chemical, e.g. local physicalatmosphere, water, soil Living: ecological community – set of species interacting within ecosystem Process Cycling of chemical elements Flow of energy 5 Change - Succession 4 Non-living/Abiotic Non-living/Abiotic Factors The The degree to which abiotic factors are present or absent/high or low affects the ability of organisms to survive. Since Since each individual in a population/species may have may have a slightly different (genetically determined) determined) response to a particular factor, populations will differ in their responses to the abiotic environment, reflecting the sum of individual variation The The nature of a particular ecosystem will be a result of this underlying variation in both abiotic factors and populations’ responses 6 1 2/17/2011 Different individuals thriving under different environmental regimes For every environmental factor and every population . . . The optimum represents the conditions favoured by the majority of organisms in the population. At higher or lower levels, individuals are under stress with only some capable of persisting. Beyond the limit of tolerance no individuals can of tolerance, no individuals can survive, hence the species will not be found in these kinds of environments # There is an environmental optimum (the level at which the majority of organisms do best) where we see the largest population sizes. At higher or lower levels of a factor, organisms do less well (they are under stress). At further extremes (the limit of tolerance), they do not survive. 8 15 7 For For any particular population, numbers (or density) will be highest where all relevant environmental conditions are optimal. Some Some organisms have generally wide ranges of tolerance (generalists). Other have (generalists). narrower ranges (specialists). (specialists). Those Those with wide tolerance ranges (generalists who have broad niches) can live niches) in a variety of habitats. Those with narrower ranges (specialists with narrow (specialists niches) niches) have more restricted distributions. 9 The small % of the world’s species that have actually recovered from endangered status suggests we’re not very good at it! 10 Feeding relationships: food webs Ecological Community Interacting Species Restricting Restricting any one of the many different environmental factors that influence an organism will limit the population e.g. plants e.g. plants need water, light, nutrients and proper temperatures temperatures for growth growth Even Even if water, nutrients and light are optimum, the plants cannot survive and prosper if temperatures are above or below their limit of tolerance Ecologists Ecologists expend considerable effort trying to quantify species niches and the population’s most likely limiting factor(s) Pelagic Food chains – energy, chemical elements and components transferred from creature to creature Food webs – more complex cases Keystone species 11 Note that feeding relationships include both herbivory (eating plants) and predation (eating animals) Terrestrial Detrital 12 2 2/17/2011 In spite of the variety and apparent complexity of foodwebs, foodwebs, they all have the same underlying trophic pattern Secondary (2o) consumers or carnivores (also heterotrophs) heterotrophs) Primary Primary (1o ) consumers, grazers grazers or or herbivores (heterotrophs) (heterotrophs) Producers, usually plants or autotrophs autotrophs (make own food) decomposers Decomposers (“tertiary” consumers) are also heterotrophs The relationship between producers and consumers is one we have seen before as the carbon cycle Autotrophs (selfAutotrophs (self-feeders) ‘feed’ themselves through photosynthesis (the process of turning inorganic carbon into organic carbon and capturing energy) CO2 + H2O <=> C6H12O6 + O2 Heterotrophs Heterotrophs (other feeding) ‘feed’ themselves by consuming organic carbon already fixed by autotrophs and extracting its energy via respiration – that energy is then available for growth reproduction, etc. (though they have to get rid of the CO2) C6H12O6 + O2 <=> CO2 + H2O <=> 13 14 14 Energy also helps us understand the limits of food webs Energy flow in ecosystems: Though we have been talking about ‘consumption’ (as in who eats whom) what’s really moving among species is energy (which cannot be ‘consumed’) The The 2nd law of thermodynamics tells us that there will be an inevitable loss of “useful” energy (or an increase in entropy) with the progressive movement to higher th progr mo and and higher trophic levels. Eventually Eventually there will not be sufficient energy to support an additional trophic level. Most Most ecosystems are characterized by 3 (terrestrial) or 4 (aquatic) trophic levels. 15 Thermodynamics also helps us understand the ecological consequences of ever increasing meat consumption by humans • The graph tells us that it takes up to 16 kg of grains to produce 1 kg of beef and 3 to 6 kg to produce 1 kg of pork, turkey, chicken or eggs (40% of the world’s grain is fed to livestock) livestock) • 78 calories of fossil fuel produces 1 calorie of beef; 35 calories produce 1 calorie of pork; 22 calories produce 1 calorie of poultry; 1 calorie of fossil fuel produces 1 calorie of soybeans • It takes 3 to 15 times as much water to produce animal protein as it does plant protein Leitzmann, C. (2003). American Journal of Clinical Nutrition, 78:657S-659S. 17 16 16 Terrestrial vs aquatic ecosystems The The predominant biomass in forests is in trees (the bottom of the food web) Yet Yet the predominant biomass in aquatic systems is in fish/mammals (oceans) at the top of the food chain Something Something significantly different is going on on in these different systems! Furthermore, Furthermore, in between these two extremes are grassland/savannah systems where the predominant constituent of biomass are the herbivores (grazers like buffalo, antelope, etc.), the “middle” of the etc foodweb How How do we understand these differences? 18 18 3 Numbers of species Numbers of species 2/17/2011 In terrestrial ecotones we often find many species common to both adjacent systems In contrast, aquatic ecotones often contain highly specialized species found in neither of the adjacent systems 19 In spite of boundaries . . . and differences All All ecosystems remain interconnected and interdependent Terrestrial biomes are connected by rivers Sediments/nutrients from land wash into aquatic ecosystems All share a common hydrologic cycle and a common atmosphere All All species on Earth (along with their environments) could be considered one vast ecosystem (landscape): the biosphere But But inherently impractical as a unit of study 20 If everything is connected to everything else, . . . How How many ecosystems can be degraded or destroyed before we see effects on the entire biosphere? To To what extent can basic global elements be be altered (e.g. the atmosphere and its the temperature, the ocean and its chemical composition) before all ecosystems are affected? affected? What What are the implications for the longlongterm persistence of humans? 21 22 22 The sea otter as a keystone species: an observational observational experiment Keystone species 1. As the keystone is essential to the physical integrity of a stone arch (even though it is only one stone), a keystone species has a critical role in maintaining the overall relationships within an ecosystem ecosystem (even though is though is not a numerically dominant species). 2. A strongly interacting species whose top-down effect on species diversity and competition is large relative to its biomass. Sea otter feeding on urchins urchins kelp 23 4 2/17/2011 Kelp forests With the loss of sea otters Kelp forests are unique, diverse habitats utilized by numerous species. Sea otters do not affect kelp directly. They help maintain the integrity of kelp forest ecosystems by controlling sea urchins who do eat kelp. 25 Shemya/Amchitka Shemya/Amchitka Island comparision Urchin numbers grow exponentially As you might predict, they quickly drive their food resource (kelp) to extinction A number of other species are then lost with the loss of kelp In addition, large mammals lose protected habitat during storms. 26 In the sad next chapter . . . Sea otters were extirpated on much of the west coast. Concomitantly, kelp forests declined as did populations of economically valuable clams, mussels, crabs and some fish species. Puffins and other fish eating birds were also affected. Kelp forests also provide a variety of ecosystem services, protecting shorelines from wave erosion and providing a storm refuge for numerous species including whales, seals, sea lions. 27 While sea otter numbers have rebounded in lower BC and the US west coast, otter numbers – particularly in Alaska - are in decline Killer whales – which normally would eat sea lions seem – seem to have switched to preying preying on otters because sea lion/seal populations have crashed (down to 10% of former numbers)! The most likely explanation is food web alterations associated with changes in sea temperatures Rolf Hicker 28 (www.whale-images.com/steller-sea-lion.htm (A) Changes in sea otters over time at several Aleutian islands (B) sea urchin biomass (C) grazing intensity (D) kelp density The cartoon on the left shows how the kelp forest ecosystem was organized before the sea otter's decline and the one on the right shows how this ecosystem right shows how this ecosystem changed with the addition of killer whales as an predator (Heavy arrows represent strong trophic interactions; light arrows represent weak interactions) Estes et al. (1998) Science 29 29 5 ...
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