Transcript community
Ch. 47 – Community Ecology 1 Community Ecology Concept of Community A community is an assemblage of populations interacting with one another within the same environment Composition is a thorough listing of various species in the community Species Diversity includes: 1. Species Richness – total number of different species in the community 2. Relative Abundance – proportion of the total population represented by each species 2 The various animals and plants surrounding this watering hole are all members of a savanna community in southern Africa Figure 53.1 Community Structure Coniferous Forest 4 Rain Forest 5 Two different communities can have the same species richness, but a different relative abundance A B A community with an even species abundance is more diverse than one in which one or two species are abundant and the remainder rare C D Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 Figure 53.11 A: 80% B: 5% C: 5% D: 10% Community Ecology Structure of the Community Competition When two species compete, the abundance of both species is negatively impacted Predation (Herbivory – plant predation) ● One organism, the predator, eats another called the prey. Parasitism One organism, the parasite, feeds ON another called the host. These tend to increase the abundance of the predator (or parasite) and reduce the abundance of the prey (or host) ● 6 7 Community Ecology Habitat and Ecological Niche Habitat The area an organism lives and reproduces in Ecological niche The role a species plays in its community - Includes its habitat, and - Its interactions with other organisms Fundamental niche - All conditions under which the organism can survive & reproduce Realized niche – part of the fundamental niche that the species actually occupies 8 Feeding niches for Wading Birds 9 Community Ecology 10 Competition Between Populations Interspecific competition When members of different species try to use a resource that is in limited supply (food, light, etc.) Competitive Exclusion Principle No two species can indefinitely occupy the same niche at the same time Resource Partitioning decreases competition Can lead to character displacement. This is the tendency of a characteristic to become more divergent when species are together. 11 Competition between two laboratory populations of Paramecium Both grow fine separately but only P. aurelia survives when they are grown together 12 Character Displacement in Finches on the Galápagos Islands 13 Niche Specialization Among Five Species of Coexisting Warblers Competition Between Two Species of Barnacles Connell removed the larger Balanus individuals. The smaller Chthamalus barnacles moved down & survived equally well in both places 14 Competition Between Two Species of Barnacles EXPERIMENT 15 RESULTS Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland. When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area. High tide High tide Chthamalus Balanus Chthamalus realized niche Chthamalus fundamental niche Balanus realized niche Ocean Ocean Low tide Low tide In nature, Balanus fails to survive high on the rocks because it is unable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata. CONCLUSION The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realized niche of Chthamalus much smaller than its fundamental niche. Community Ecology Predator-Prey Interactions Predation One living organism, the predator, feeds on another, the prey -Predator is frequently larger -Predator population is usually smaller than the prey population -Predator has lower reproductive rate -Prey is usually consumed in its entirety Presence of predators can decrease prey densities, and vice-versa 16 Predators 17 18 Predator-prey Interaction Between Paramecium caudatum and Didinium nasutum Paramecium & Didinium placed in same culture. Didinium ate all the Paramecium and then died of starvation 19 Predator-prey Interaction Between a Lynx and a Snowshoe Hare When hares have adequate food & there are no predators, the cycling stops. Hares given adequate food but with predators; they still cycle Predators excluded but no food was given to hares; cycling stopped Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors. 20 Predator populations may be influenced by availability of prey - as more prey is available, they reproduce more and their population increases. When the predator population gets too high and they eat all the prey, their population falls. Prey populations may be influenced by 1.Predation 2. Fluctuations in the availability of the plants they feed on 21 Prey may not be regulated by predators. Their population may increase until they run out of resources, then their population crashes. As a result the predator population soon declines because of lack of food availability. Feeding adaptations of predators include: claws, teeth, fangs, stingers, and poison 22 Some predator-prey interactions lead to coevolution: a series of reciprocal adaptations in two species Predator Adaptations 23 Community Ecology 24 Prey Defenses Mechanisms that thwart the possibility of being eaten by a predator. Some examples: - Spines - Tough Epidermis - Poisonous Chemicals - Camouflage – ability to blend into the background. Have cryptic coloration. - Bright Coloration - Flocking Behavior 25 Spines as protection for plants against herbivory Chemical Defenses in Plants Poison Oak and its rash 26 Camouflage in the Anglerfish 27 Cryptic Coloration 28 Cryptic Coloration 29 Cryptic Coloration 30 Anti-predator Defenses Poisonous skin + Warning coloration Large false head 31 False eyespots Aposematic (warning) coloration All these snakes are poisonous 32 Community Ecology 33 Mimicry One species (mimic) resembles another species (model) that possesses an overt anti-predator defense. Two main types: 1. Batesian Mimicry - Mimic lacks defense of the organism it resembles 2. Müllerian Mimicry - Mimic shares same protective defense as its model Mimicry Among Insects with Yellow and Black Stripes a, b, & c are examples of Batesian mimicry because they do not have the capability to sting. Fly Moth Bumblebee Beetle Yellow jacket d & e are Mullerian mimics since they both use stinging as a defense 34 In Batesian mimicry 35 A palatable or harmless species mimics an unpalatable or harmful model re 53.7a, b (b) Green parrot snake (a) Hawkmoth larva Batesian Mimicry (flies, beetles & ants mimic 36 wasp) Wasp Batesian Mimicry Poisonous models on left Harmless mimics on right 37 In Müllerian mimicry Two or more unpalatable species resemble each other (a) Cuckoo bee Figure 53.8a, b (b) Yellow jacket 38 Community Ecology 39 Symbiotic Relationships Interactions in which there is a close relationship between members of two species. Frequently one species lives in or on another. Three main types of symbiosis are: - Parasitism - Commensalism - Mutualism Community Ecology 40 Symbiotic Relationships Parasitism - Parasite derives nourishment from a host, and may use host as habitat and mode of transmission - Endoparasites - live inside host - Ectoparasites - live on outside of host Natural selection favors parasites that infect but don’t kill their hosts. Parasites Leech41 Flea Mosquito Ringworm The Life Cycle of a Deer Tick Human may end up with Lyme Disease 42 Community Ecology 43 Mutualism A symbiotic relationship in which both members of the association benefit Need not be equally beneficial to both species - Cleaning Symbiosis - one animal cleans another - E. coli in human intestines - Protozoans in termite intestines - Mycorrhizae between roots & fungi - Ants & bullhorn acacia trees Often help each other obtain food or avoid predation Cleaning Symbiosis 44 45 More Cleaning Symbiosis 3.9 Mutualism Between the Bullhorn Acacia Tree and Ants 46 47 Pollination of Plants by Animals is an example of Mutualism Community Ecology Commensalism A symbiotic relationship in which one species benefits and the other is neither benefited or harmed - Remoras attach to sharks & get a free ride - Clownfish living inside of sea anemone’s tentacles - Epiphytes, like Spanish moss, live on trees Many supposed examples may turn out to be mutualism or parasitism - Inferred amount of harm or benefit that 2 species do to one another is subject to investigator bias 48 49 Whales & Barnacles Spanish Moss Remoras & Sharks Clownfish Among Sea Anemone’s Tentacles 50 Community Ecology 51 Community Development Ecological Succession A predictable pattern of change in species replacements following a disturbance - Primary Succession occurs in areas where there is no soil formation •After a volcanic eruption or glacial retreat - Secondary Succession begins in areas where soil and life are already present •Like when a cultivated field returns to nature Pioneer Species - first species to colonize an area (frequently lichens & moss) Primary Succession occurs after glaciers retreat 52 Canada Grand Pacific Gl. 1940 Alaska 0 1912 1948 Miles 1941 1 899 1907 5 1931 1879 1911 1948 1900 1879 1935 1879 1892 1913 1949 1860 Reid Gl. 1879 Johns Hopkins Gl. Glacier Bay 1830 1780 1760 Pleasant Is. 10 Primary & Secondary Succession at Glacier Bay, Alaska (a) Pioneer stage, with fireweed dominant (b) Dryas stage 60 50 Soil nitrogen (g/m2) 40 30 20 10 0 Pioneer Dryas Alder Successional stage (d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content. Spruce (c) Spruce stage 53 Primary Succession 54 55 Primary Succession Primary Succession 56 Secondary Succession in a Field 57 Secondary Succession in a Forest 58 Secondary Succession in a Forest 59 Community Ecology 60 Community Stability Community stability can be recognized in three ways: Persistence through time – when a community remains just about the same year after year Resistance to change – when trees are able to regrow leaves after insect infestation Recovery once a disturbance has occurred – when a community, like chaparral, quickly returns to its normal state after a fire Community Ecology 61 Community Stability Decades ago, most ecologists favored the traditional view that communities are in a state of equilibrium. However, recent emphasis on change has led to a nonequilibrium model. This describes communities as constantly changing after being buffeted by disturbances. Disturbances affect all communities - Floods, fire, glaciers, volcanic eruptions can change communities greatly 62 Fire is Often Necessary to an ecosystem (a) Before a controlled burn. A prairie that has not burned for several years has a high proportion of detritus (dead grass). (b) During the burn. The detritus serves as fuel for fires. (c) After the burn. Approximately one month after th controlled burn, virtually all of the biomass in this prairie is living. Yellowstone Fire of 1988 (a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance. 63 ( b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground. Predation, Competition, and Biodiversity Community Ecology 64 Keystone species are organisms that play a great role in maintaining function & diversity of an ecosystem. They are not necessarily abundant, but exert strong control on a community by their ecological roles Keystone predator may help to maintain diversity by reducing the numbers of the strongest competitor in a community -This helps to prevent exclusion of weaker competitors, and prevents strongest competitor from becoming too dominant Effect of a Keystone Species Pisaster seastars were removed from experimental tidepools but were left in control areas. Diversity decreased in experimental areas 65 66 Effect of Sea Otters on Ocean Communitie Without sea otters there might not be any kelp beds Figure 53.17 Food chain before killer whale involvement in chain Otter number (% max. count) 100 80 60 40 20 0 (a) Sea otter abundance Grams per 0.25 m2 400 300 200 100 0 (b) Sea urchin biomass 10 Number per 0.25 m2 Observation of sea otter populations and their predation shows the effect the otters have on ocean communities. 8 6 4 2 0 1972 1985 1989 1993 1997 Year (c) Total kelp density Food chain after killer whales started preying on otters Predation, Competition, and Biodiversity Community Ecology 67 Exotic species Introduction of exotic (alien) species into new areas Can provide many examples of competition Can lead to a reduction in biodiversity & even extinction of organisms 68 Exotic species – Africanized honey bee They are replacing the less aggressive honey bees used in agriculture Exotic species – Brown tree snake69 Spread of Brown tree snake on Guam Snake eats native birds causing extinction Exotic species - Kudzu It grows on top of trees & objects. Can kill trees. 70