Ecology PDF

Community composition & particular species found within a community Some species are naturally abundant and others are rare not imp....

Community composition & particular species found within a community Some species are naturally abundant and others are rare not imp. more Some communities are dominated by one or a few species common in Canada (temperate zone) but not in tropics Some communities are naturally species-rich while others are species-poor 6  Community composition Species richness: the number of species present in a community Evenness: the relative abundance of species in how many present is community Species diversity: an integrated measure of both richness and - evenness… and the focus of chapter 12 Tropical rainforests are - characterized by high richness, low evenness 7  Graph imp for Rank abundance looking at eveness More complete picture of community diversity when abundance is plotted against rank really ↓ common way more abundant than others Yukon grasslands Israel desert HIGH EVENESS > - slightly lower but almost LOW the same EVENESS ↓ Snewed species richness curve # of most abundant individuals organism rarest organism FIGURE 9.10 8  Community structure Many communities have dominant species for each trophic level A dominant species is the most conspicuous Dominant prairie plants: and abundant one in a grasses and forbs community highest biomass > - In many cases, the dominant species has the greatest influence on community structure Dominant herbivore: and function buffalo; carnivore: wolf 9  Keystone species OUTSIZED INFLUENCE Keystone species have disproportionately large effect on community structure Removal of a keystone species leads to change in community composition Stone at the top of the are that is carved to perfectly hold all stones in place 10  Keystone species Example: Starfish in rocky intertidal zones use sharp teeth to on muscles never very abundant graze if removed > - two Species of muscles took off most abundant returned - eat muscles all , Six species started being present in high levels FIGURE 9.34 11  Keystone species Example: Beavers in northern forest communities They influence habitat diversity as ecosystem engineers entire change landscape 12  Niche Niche: all environmental factors that limit a species’ distribution, growth, and reproduction Fundamental niche: total range of conditions under which a species can establish, grow, and reproduce Realized niche: actual range of conditions, influenced by competitors 13  Niche There are many definitions of “niche”: “The physical space occupied by an organism or species.” - Chapter 2 14  Niche There are many definitions of “niche”: “An animal’s place in the biotic environment, its relations to food and enemies… and the status of an organism in its communities” - Charles Elton 15  Niche G. Evelyn Hutchinson provided a formal definition of a niche: A multidimensional space of environmental factors that a species can tolerate, within which it lives, and to which it is well adapted G. Evelyn Hutchinson “father of American ecology” (1903-1991) 16  Niche G. Evelyn Hutchinson provided a formal definition of a niche: A multidimensional space of environmental factors that a species can tolerate (the - - fundamental niche), competiwithin tio which it lives (the realized niche), and to - G. Evelyn Hutchinson which it is well adapted - “father of American ecology” (1903-1991) 17  Niche Multidimensional space of environmental factors dimensional plant one niche axis of moisture single too dry can't survive - FIGURE 9.18 18  Niche Multidimensional space of environmental factors too cold -> can't survive too not - can't survive middle - perfect FIGURE 9.18 19  Niche Multidimensional space of environmental factors FIGURE 9.18 20  Niche overlap species a , b c , have completely diff niches Although species may overlap closely along certain niche axes, they are separated along others temperature Species C- low temp , low moisture Carctic tundra) Species Bo moisture moderate temp , high (temperate rainforest) tolerate Species A s interm. Moisture , high temp large highest (mediterranean) tolerate overlap in moisture levels lower moisture niches levels intermed. moisture FIGURE 9.19 levels moisture 21  Idea : have Species identical that niches Competitive exclusion cannot coexist Georgii Gause (1910- Yeast species 1: Saccharomyces 1986) found that one species outcompetes another in mixed populations lower cure Still achieve M He proposed the idea of competitive exclusion, Yeast species 2: Schizosaccharomyces that species with identical niches cannot coexist if let coexist for organisms long period of time of would seek one the species out competed and disappear from that if FIGURE 5.23 community 22 had identical niche  Competitive exclusion The competitive exclusion principle states that in a stable environment, no two species can occupy the Galium saxatile same niche—one will be dominates at acidic sites eliminated Example: two species of Galium bedstraw in Britain Galium sylvestre dominates at basic sites ↳ would in dominate 23 basic Sites (Outcompete)  Competition in communities Competitive release: a species can spread out, and occupy a broader niche when a competitor is eliminated Meadow voles thrive in habitats close to water Example: If meadow voles are removed from an area, mountain voles experience competitive release, and expand to their wetter habitats Montane voles thrive in dry habitats 24  Fundamental vs realized niche Competitive Principle : Exclusion is the blue species competitively excluding orange species /close to surface) Fundamental niche is full No competition (fundamental) range of environmental Biomass tolerances Realized niche is the range after restriction by competitors With competition (realized) blue remove Example: fundamental would orange Biomass experience comp release niche of two cattail and move to occupy at / above species extends to dry surface habitats land; realized niche restricted by competitor FIGURE 9.23 25 small size body and beaks eat insects Cape May Warbler (Dendroica tigrina) 27  Bay-breasted Warbler Blackburnian Warbler (Dendroica castanea) (Dendroica fusca) Black-throated Green Warbler Yellow-rumped Warbler (Dendroica virens) (Dendroica coronata) 28  Resource use by warblers in same niche ?? see warblers living Do wood warblers defy the competitive exclusion principle? see where of a type warbler is foraging Robert MacArthur Canadian-born ecologist (1930-1972) 29  tree ! of ; separate diff the niches all found in parts Resource use by warblers FIGURE 9.25 30  Resource use by warblers > - insects Resource partitioning they need allows warblers to - coexist diff species are of foraging the tree on diff rise to parts diff realized giving niches between them d& support for COMPETITIVE EXCLUSION Robert MacArthur Canadian-born ecologist (1930-1972) 31 Bicoloured antbird Ocellated antbird Example of NICHE PARTITIONING : rise to diff realized giving niches organisms among Spotted antbird32 even Fundamental that have overlapping niches.  Facilitation & one organism's presence enhances the for oppurtunity other organisms to exist there Outside of competition, organisms may also interact in positive ways, called facilitation: don't well in Soil grow very Hemlock uses fallen logs > - to regenerate in moss- rich forests bygrowth facilitated that organism came before. it Simultaneous flowering increases pollinator attraction all flower at the same pollinators time attract Spruce survive the harsh Nitrogen-fixing species environment of the promote growth of other tundra under birch shrubs species plants other nitrogen the crave for their better than in the open production 33 34  Intermediate disturbance hypothesis Species richness is the highest at intermediate levels of disturbance At high levels of disturbance, many species fail to establish At low levels of disturbance, competitively superior species suppress others FIGURE 9.30 35  Intermediate disturbance hypothesis Example: algal community in the intertidal zone rock is substrate for to algae grow Three species of algae on boulders of Number of plants different size intermediate levels of disturbance that rise to the most give individuals Small Medium Large Small Medium Large lots of disturbance Boulder size 36 low disturb. small rocks -> turned FIGURE 9.31 big rocks over all and the scraped time  Intermediate disturbance hypothesis Example: plant species diversity in plots that experience different degrees of browsing by rabbits in a sand-dune community to water of plants send roots out highest measures species intermediate richness at the > - stabilize dunes levels of disturbance low high FIGURE 9.32 high levels of biodiversity - intermediate levels of disturbance 37  Top-down vs bottom-up Top carnivore Herbivore + + FIGURE 9.46 autotrophs 38  Top-down vs bottom-up Top-down hypothesis (Wolf) (consumer control): abundance of a species is limited by consumers Decrease in carnivores leads to increase in herbivores Bottom-up hypothesis (resource control): consumer abundance (herbivore or carnivore) determined by food limitation Mast years of acorns leads to increase in rodents 39  Trophic cascades Serial changes in species abundances and distributions at lower trophic levels, occurring in response to changes at a higher level 40  Summary Richness, evenness, and diversity are measures of community composition Dominant species are most conspicuous or abundant; keystone species have disproportionately large effects Multi-dimensional understanding of niches is critical for understanding communities Regulation can be understood as a top- down or bottom-up process 41