Community. Biological communities. A biological community refers to all the species that occur together at any particular locality.

Transcription

1 Biosphere Population Community Ecology Chapter 54 Ecosystem Organism Community 1 2 Community A biological community refers to all the species that occur together at any particular locality. Biological communities 3 4 Gleason & Clements Individualistic Holistic Individualistic Holistic 5 6 1

2 Individual species in a community respond independently to changing environmental conditions. A synchronous change of species in communities exist only when sharp changes of environmental conditions occur. Number of stems per hectare 4 2 Wet Moisture gradient Dry Black oak Poison oak Iris Douglas fir Hawkweed California fescue Snakeroot Normal soil Canyon live oak Collomia Ragwort Yarrow Buck brush Small fescue Fireweed Knotweed Ecotone Serpentine soil 7 8 Attributes of ecological communities Biodiversity: number & evenness Biodiversity The number and evenness of species. kingfisher merganser great blue heron otter The niche concept The role of interspecific interactions Food web structure The feeding relationships among species. steelhead roach water scavenger beetle larva tuft midge frog tadpole stickleback garter snake snail newt crayfish dipper caddis fly larva Succession The change of communities through time. 9 diatoms green algae blue-green algae 1 Biodiversity measures the number of species and their evenness Most species in a community are rare Species richness may be equal, but relative abundance may be different

3 Biodiversity: community 1 > 2 Exercise: What factors determine the occurrence of a species in a community? kingfisher merganser great blue heron garter snake otter dipper steelhead roach stickleback newt caddis fly larva frog tadpole water scavenger beetle larva tuft midge snail crayfish 13 diatoms green algae blue-green algae 14 First, a species needs to be able to tolerate the local physical-chemical environment. Second, the environment must provide required resources, such as food. + required resources ~ the fundamental niche A niche + required resources

4 Joseph Grinnell (UC Berkeley) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The distribution patterns of Chthamalus & Semibalanus High tide Chthamalus Low tide Semibalanus 19 2 Joseph H. Connell (UC Santa Barbara) Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Exercise: Is this range the fundamental niche of Chthamalus? How do you know? High tide Chthamalus Low tide Semibalanus High tide Low tide Let s do a removal experiment [1] removing Chthamalus Chthamalus Results: What does the removal experiment tell you? High tide Low tide Chthamalus After removing Chthamalus Semibalanus [2] removing Semibalanus Semibalanus After removing Semibalanus

5 Realized Niches Actual niche utilized by an organism is influenced by competition, predation, parasitism, mutualism, etc.. Biological interactions change niche space, thus contribute to the structure of a community. Fundamental vs Realized Niches High tide Chthamalus Low tide Semibalanus 25 Fundamental niches Realized niches 26 Predation often reduces niche space ~ the realized niche Biotic interactions limiting + required resources Ghost of competition past Ghost of predation past Exercise: What d happen if 2 species had overlap niches, e.g. steelhead & roach? The fundamental niche of a species may shift due to consistent biological interactions over evolutionary time scale. Thus, the effects of competition or predation are no longer exist in the present day. kingfisher steelhead merganser great blue heron roach stickleback garter snake newt otter dipper caddis fly larva Species as we see them today are products of biological interactions over evolutionary times. 29 frog tadpole water scavenger beetle larva tuft midge snail crayfish diatoms blue-green algae green algae 3 5

6 Outcomes of interspecific competition If niche overlap extensively, then, to coexist, the shared resources must not be limiting. Otherwise,.. One species may be driven to extinction (competitive exclusion). Principle of Competitive Exclusion When resources are limiting, no two species utilizing the same niche can coexist indefinitely. one will eventually eliminate the other Or, one or both species has to shift their niches by changing their behavior (resource partitioning). Sometimes, morphology change as well (character displacement) to enhance resource partitioning Georgyi F. Gause (Moscow Univ.) Competitive Exclusion Among Paramecium Alone Population density P. aurelia P. caudatum Days Days 2 P. caudatum P. aurelia 33 Together Population density Days 34 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. If competitive exclusion did not occur, Alone Together resource partitioning must exist P. caudatum P. bursaria Days Days Population density P. caudatum P. bursaria 8 12 Days 16 2 Eat bacteria Eat yeasts 35 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Either way, competition reduce population sizes, thus, change relative abundance and community structure. 36 6

7 Consequences of long-term competition The fundamental niche of a species may shift under long-term interspecific competition through 2 processes: Resource Partitioning Species living in the same area (sympatric species), over time, evolve behavioral mechanisms that partition available resources to avoid direct competition. Resource partitioning Character displacement Resource Partitioning the sympatric species have subdivided the niche Robert MacArthur (Princeton Univ.) RESOURCE PARTITIONING OF INSECT-EATING WARBLERS Cape May warbler Bay-breasted warbler Myrtle warbler 39 4 Resource partitioning of insect-eating lizards Character displacement Sympatric species tend to exhibit greater differences in morphology than allopatric species (species that live apart from each other) to avoid direct competition

8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Character Displacement Does the diversification of Darwin s finches involve resource partitioning & character displacement? Individuals in each size class (%) Los Hermanos Islets Daphne Major Island San Cristobal and Floveana Islands Finch beak depth (mm) G. fuliginosa Alone G. fortis Alone G. fuliginosa and G. fortis Sympatric Exercise: Use an analogy to describe niche to your friend. kingfisher merganser great blue heron garter snake otter dipper Mode of interspecific competition Exploitative competition e.g. Paramecium compete for food the 2 species consume shared resources The 2 species don t need to see each other steelhead roach water scavenger beetle larva tuft midge frog tadpole stickleback snail newt crayfish caddis fly larva Interference competition e.g. barnacles compete for space the 2 species fight over resources (space) there are face-to-face confrontations diatoms green algae blue-green algae Exploitative competition Hey, don t drink too fast! Interference competition Hey, you pinch my straw!

9 Kangaroo rats and other desert rodents Removal experiments are the strongest tests of the existence of interspecific competition Number of other rodents Kangaroo rats removed Kangaroo rats present Detecting Interspecific Competition Negative effects of one species on another do not automatically indicate competition. Presence of one species may attract a predator that consumes both, causing one species to have a lower population size than the other. (apparent competition) Exercise: So, how does competition affect community structure? kingfisher steelhead merganser great blue heron roach frog tadpole water scavenger beetle larva stickleback garter snake snail newt otter crayfish dipper caddis fly larva tuft midge 51 diatoms green algae blue-green algae 52 Predation also affects community structure. Exercise: What d happen to the community when heron reduce roach? kingfisher merganser great blue heron garter snake otter dipper kingfisher merganser great blue heron otter garter snake dipper steelhead roach frog tadpole water scavenger beetle larva tuft midge stickleback snail newt crayfish caddis fly larva steelhead roach frog tadpole water scavenger beetle larva tuft midge stickleback snail newt crayfish caddis fly larva diatoms green algae blue-green algae 53 diatoms green algae blue-green algae 54 9

10 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Predators reduce the population size of prey, and often induce top-down trophic cascades. Number of individuals Paramecium Didinium Trophic cascades are a key feature in community dynamics. We will talk about it in ecosystem ecology Days Coevolution The interdependent evolution of two or more species. Particularly, arms races between predators and prey drive evolutionary changes and remarkable adaptations in both predator and prey species, and promote species diversity. Plant defenses against herbivores -- Morphological defenses Plant defenses against herbivores -- secondary compounds Some herbivores can breakdown secondary compounds Mustard oils cabbages cabbage butterfly

11 Herbivores make use of secondary compounds Herbivores make use of secondary compounds Cardiac glycoside milkweed Monarch butterfly Prey defenses against predators Chemical defenses Chemical defenses Morphological defenses Cryptic (camouflage) coloration. Warning (aposematic) coloration. Mimicry Camouflage! Can you see them? Warning! Dare you eat them!

12 Batesian mimicry is where a harmless species mimics a harmful one. Müllerian mimicry is where two or more unpalatable species resemble each other. Danaus plexippus Limenitis archippus Müllerian mimicry & Batesian mimicry In addition to competition, predation & herbivory, there are other types of species interactions 69 7 Cannibalism Commensalism Epiphytes Barnacles on whales

13 Mutualism Parasitism -- ectoparasites Parasitism -- endoparasites Insect Parasitoid Parasites with complex life cycles often manipulate host behavior Mutualism turns parasitism

14 Interactions Among Ecological Processes Predation may reduce competition Parasitism may alter competition Indirect effects Presence of one species may affect a second species through interactions with a third species. Rodents What d happen to ants if you removed rodents? Ants Large seeds Small seeds 8 Number of ant colonies Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig (TE Art) Rodents removed Rodents not removed Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig (TE Complex Art) indirect interaction Ants Rodents + + Oct 74 May 75 Sep 75 May 76 Aug 76 Jul 77 Sampling periods Large seeds Small seeds Keystone species A species whose absence would bring about a significant change in the community. Top predators in a community are often keystone species (e.g. sea stars affect the diversity of tidal pool communities). A tidal pool community

15 After sea star removal Before After Sea stars as a keystone species Exercise: Who do you think is the keystone species in this community? kingfisher merganser great blue heron otter garter snake dipper steelhead roach stickleback newt caddis fly larva frog tadpole water scavenger beetle larva tuft midge snail crayfish 87 diatoms green algae blue-green algae 88 Ecosystem engineering Some keystone species modify their habitats to produce a particularly strong effect on community structure, e.g. beavers. Succession Biological communities change with time, usually, but not necessarily, from a simple to a more complex structure. primary succession secondary succession

16 Primary succession - occurs on bare substrates Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Soil nutrients change as succession progress Year 1 Glacial retreat 3 25 Year 1 Year 2 Nitrogen (g/m 2 ) a b c Nitrogen in forest floor Nitrogen in mineral soil Year 1 Year 1 Year 2 91 Pioneer mosses Invading alders Alder thickets Spruce forest 92 Primary succession - occurs on bare substrates Secondary succession occurs where an existing community has been cleared, but the soil is left intact Why succession occurs? Pioneer species are able to tolerate harsh conditions during early succession. Why succession occurs? Seed dispersers also aid the succession process Settled species alter the habitat which facilitate the invasion of subsequent colonizers. The habitat may be further altered that inhibit the growth of original colonizers

17 Most communities are in a state of nonequilibrium owing to frequent disturbances Marine and island communities are subject to disturbance by tropical storms We often think that disturbances have a negative impact on communities, but some communities are maintained by disturbance. Exercise: Do disturbances increase or decrease species diversity in a community? How? Species number? 99 Disturbance 1 Intermediate disturbance theory Communities experiencing moderate levels of disturbance will have greater species richness than communities experiencing either smaller or larger levels of disturbance. simultaneous successional stages dominant competitors kept at bay Exercise: What factors influence the biodiversity of this community? kingfisher steelhead merganser great blue heron roach stickleback water scavenger frog tadpole beetle larva tuft midge garter snake snail newt otter crayfish dipper caddis fly larva 11 diatoms green algae blue-green algae 12 17

18 Causes of biodiversity, so far Physical-chemical environment Biological interaction Disturbance Others? Biosphere Ecosystem Population Organism Community Dynamics of Ecosystems Chapter 55 Ecosystem ecology An ecosystem includes all the organisms living in a particular place, and the abiotic environment in which they interact. Chapter 55 Ecosystem ecology is about Biogeochemical cycles of chemical elements through ecosystems. Energy flows through ecosystems (a one-way process) Eugene Odum (Univ. of Georgia) Biogeochemical Cycles The water cycle The carbon cycle The nitrogen cycle The phosphorus cycle

19 Physical processes move elements around Biological processes move elements around Feeding Photosynthesis Decomposition Biogeochemical Cycles The water cycle The water cycle The carbon cycle The nitrogen cycle The phosphorus cycle Organisms Ice The Water Cycle By area, oceans receive ¾ and lands ¼ of precipitation. Both lands and oceans evaporate much of water back to the atmosphere. Reservoirs of water Atmosphere Ice On lands, transpiration from plants account for 9% of water back to the atmosphere. Organisms

20 Water cycling processes Groundwater Organisms Ice Groundwater (stored in aquifer) is the largest reservoir of water on lands. It is recharged via percolation of rainfall and water seeps down from lakes and streams through soil, very slowly. The flow is also very slow Mining and pollution of groundwater Human mine groundwater, thus many underground aquifers have much higher withdraw rates than recharge rates. Agriculture will be in trouble. Deforestation breaks the local water cycle In forest ecosystems, plants take up much moisture and transpire it back into the atmosphere, forming clouds. When forests are cut down, water drains from the local area instead of forming clouds. Pesticides, herbicides, and fertilizers accumulate in groundwater are virtually impossible to be removed (b/c slow turnover rate). Yet, groundwater supplies about 5% of drinking water (in U.S.). 117 The lack of rains further prevents reforestation, and may create semi arid desert (positive feedback). 118 Deforestation also causes erosions Biogeochemical Cycles The water cycle The carbon cycle The nitrogen cycle The phosphorus cycle

21 The carbon cycle Carbon Cycle Carbon cycle is based on CO 2 which makes up.3% of the atmosphere, dissolved in water, and those C locked up in organic compounds (live or dead organisms) and sediment (carbonates). 121 Most organic compounds formed as a result of CO 2 fixation (photosynthesis). About 7% of CO 2 in the atmosphere is fixed by photosynthesis annually. 122 Reservoirs of Carbon Carbon Cycle Carbon in the ecosystems cycles through photosynthesis and respiration processes. Most organic compounds are ultimately broken down, and C is released back into the atmosphere. Under natural condition, photosynthesis and respiration are proximately balanced. But we have been tipping the balance Carbon cycling processes Tipping the balance Increasing fuel consumption, and deforestation by burning are liberating carbon at an increasing rate

22 Green house effects CO 2 and global warming Biogeochemical Cycles The nitrogen cycle The water cycle The carbon cycle The nitrogen cycle The phosphorus cycle The Nitrogen Cycle I Only a few kind of prokaryotes can fix atmospheric nitrogen into forms that can be used for biological processes. Only symbiotic bacteria fix enough nitrogen to be of major significance Nitrogen fixation: N 2 + 3H 2 2NH 3 Nitrogen-fixing symbionts Nitrogen fixation: N 2 + 3H 2 2NH 3 Nitrogen-fixing bacteria form symbiotic relationship mainly with the roots of legumes (the pea family)

23 Reservoirs of nitrogen The Nitrogen Cycle II Organisms 133 After organisms die, nitrogen in organisms become soil nitrates through 2 processes carried out by decomposers. Ammonification NH 4+ (ammonium) are released during the metabolic processes of decomposers. Nitrification -- NH 4+ are converted by bacteria into NO 2- (nitrite) and NO 3- (nitrate) which can be taken up by regular plants. 134 The Nitrogen Cycle III Nitrogen fixed in soil (NO 3-, nitrate) may return to atmosphere through Denitrification, carried out by bacteria under anaerobic condition. Nitrogen cycling processes Feeding Denitrification: Bacteria get O 2 from NO 3- and release N 2 or N 2 O back to the atmosphere Tipping the balance Eutrophication The use of fertilizers, thus large amount of nitrogen, in agriculture alter the natural cycles of nitrogen

24 Biogeochemical Cycles Phosphorus Cycle The water cycle The carbon cycle The nitrogen cycle The phosphorus cycle The Phosphorus Cycle The largest reservoir of phosphates exist in rocks. Phosphates weather from rocks and soils into water. They may enter plants and animals, or are transported to oceans and accumulate in sediments. Reservoirs of phosphate Organisms Sediments & up-welling Guano deposits The nitrates and phosphates locked up in sediments, particularly those in the deep ocean floor, can be brought back only by up-welling

25 Tipping the balance Eutrophication Three times more phosphates than crops required are added to agricultural lands each year Exercise: What would happen to nutrient cycles after deforestation? When the watershed is intact The amounts of nutrient inputs from rains and snows are about equal to the amounts that flow out. When the forest is cut down Hubbard Brook Experimental Forest The nutrient inputs from rains drain from the local area Consequences of deforestation Nutrients cycle, but energy doesn t Concentration of nitrate (mg/l ) Deforestation

26 Energy flows through ecosystems Different types of producers Photo-autotrophs CO 2 + H 2 O C 6 H 12 O 6 (Energy provided by solar energy) Chemo-autotrophs CO 2 or CH 4 C(H 2 O) n (Energy provided by H 2 S+ O 2 Energy) Different types of consumers Trophic level refers to the feeding level of an organism Primary consumers herbivores, grainivores, frugivores, Higher consumers carnivores, insectivores, parasites, Detritivores -- break down dead organic material Scavengers Vultures and crabs Decomposers Bacteria and fungi Primary Productivity Green plants capture about 1% of the solar energy that falls on their leaves. In a given area during a given period of time Gross primary productivity (GPP) is the total organic matter produced by producers. Net primary productivity (NPP) is the amount of organic matter produced that is available to consumers. Biomass is the total mass of all Primary productivity of various ecosystems. organisms

27 Primary productivity of various ecosystems. Exercise: Why do they have different NPP? Low High We did not talk about the material covered in the following 2 slides. But they will show up in the final examine. Primary Productivity The productivity in a given area is ultimately determined by the amount of energy it receives. Thus, NPP often increases as the growing season lengthens. In aquatic ecosystems, light and nutrients limit primary production. In terrestrial ecosystems, temperature, moisture, and nutrients limit primary production On a local scale, nutrients in the soil can play key roles in limiting primary production. Not all NPP is consumed NPP not consumed will eventually become available to decomposers. And, not 1% of the NPP consumed by herbivores is assimilated Herbivores assimilate about 2% of consumed biomass; carnivores 5%. On average, 1% of consumed biomass is assimilate by consumers

28 The assimilation by consumers is only ~1% ~1% assimilation from one level to the next 17% Growth = assimilation 33% Cellular respiration = heat loss 5% Feces Exercise: Why most food chains contain less than 4 trophic levels? Diminishing energy due to heat loss Primary producer Primary consumer Secondary consumer Tertiary consumer Primary producer Primary consumer Secondary consumer Tertiary consumer One-way energy flow Diminishing energy due to heat loss Energy availability (NPP) affects the length of a food chain. Fig

29 Ecological Pyramids Exercise: Why are top predators rarer than lower consumers? Moving up a food chain, you generally find fewer individuals, lower total biomass, and lower total energy at each successive trophic level Pyramid of numbers Pyramid of biomass 1 11 Carnivore Herbivore Decomposer (5 g/m 2 ) Second-level carnivore (1.5 g/m 2 ) First-level carnivore (11 g/m 2 ) 4,,, Photosynthetic plankton Herbivore (37 g/m 2 ) Photosynthetic plankton (87 g/m 2 ) Pyramid of energy Here is a good reason to be a vegetarian Decomposer (389 kcal/m 2 /yr) First-level carnivore (48 kcal/m 2 /yr) Herbivore (596 kcal/m 2 /yr) Photosynthetic plankton (36,38 kcal/m 2 /yr)

30 Trophic cascade The effect of one trophic level flows up or down to other levels. Top-down effects Bottom-up effects Three-level top-down cascade Trout Invertebrate -- Algae 175 No Trout No Trout 176 Four-level top-down cascade Predatory fish Damselfly nymph Algae-eating insect Algae Damselflies (number/m 2 ) Chironomids (number/g algae) Algae (g/m 2 ) Fish added No fish added before after fish addition 177 Exercise: In a imaginary state, people love to hunt deer hunting. They hate the wolves that take their deer. Wolves are bad. So they do everything to get rid of wolves. What would happen if wolves disappeared? 178 Sand County Almanac By Aldo Leopold I have lived to see state after state extirpate its wolves. I have watched the face of many wolfless mountain, and seen the south-facing slopes wrinkle with a maze of new deer trails. I have seen every desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddle horn. 179 Bottom-up effects Three levels Increase the amount of light, increase predator biomass Predator biomass Herbivore biomass Vegetation biomass Amount of light 18 3

31 Bottom-up effects Four levels Increase productivity, increase food-chain length Exercise: Why are there portions of the curves where vegetation biomass does not increase as productivity increases? Productivity 181 Productivity