Lecture 3

Conservation BiologyBIOL3620Lecture 3Biodiversity Continued… Primack - Chapters 2 and 3 2Ecosystem DiversityWithin communities species play different roles and differ in requirements for survivalFigure 2.9 In this illustration, each animal species lives at different depths and in association with certain structural features 3Ecosystem DiversityLimiting ResourcesThere may be an array of food sources available but if an organism feeds only on one rare food source, organism may not be able to survive and reproduceWhen a REQUIRED resource RESTRICTS population size of a species itbecomes a limitingresourceE.g. Roostingrequirements of bats 4Ecosystem DiversityResources may become limiting on an occasional basisE.g. Water not normally limiting resource in rainforestBut occasionally, periods of drought last for weeks or sometimes monthsWater then becomes a limiting resourceplants and animals requiring constant water supply will disappear“Amazon Rainforest Carbon Sink Threatened By Drought” (Science Daily required reading) 5Ecosystem DiversityEcological Succession – gradual process of change in species composition, community structure, soil chemistry and microclimate that follows natural and human-caused disturbances.E.g. Following hurricane or loggingEarly succession species ? sun-loving butterflies, annual plantsLess canopy, more sun, high temperatures, low day-time humidityMid to late succession species ? Shade tolerant, moisture requiring wildflowers, catepillars that feed on wildflowers, tree hole nesting birdsMore canopy, more shade, more moisture, more humidity, more dead trees. 6Ecosystem DiversitySuccessional processes may be natural, human induced or a combination of bothE.g. Natural succession in grassland and forest community:FOREST FIRE, NATURAL DROUGHT CYCLES, GRAZING BY ELKE.g. Human caused succession in grassland and forest community:HUMAN-CAUSED FOREST FIRES, CATTLE GRAZING, ROAD CONSTRUCTION. 7Ecosystem DiversitySpecies Interactions within Communities:Competition and predationPredators can reduce prey density and even eliminate prey species from certain areasPredators can also indirectly increase number of species in a community:Keep density of each species so low that no competition occursE.g. Pisaster (seastar) inmarine intertidal system; keeps the population in check and you have an increase in species diversity.CLASSIC 1966 STUDY: Feeds on 15 Species of Molluscs# of molluscs increased 8Ecosystem DiversityCompetition, predation and carrying capacityCarrying capacity – The number of species that the resources or an ecosystem can support.In many communities, predators keep certain species below the carrying capacityE.g. Wolveshttp://images.google.com/imgres?imgurl=http://www.man-in-a-hurry.com/images/wolf%2520kills%2520deer.jpg 9Community Organization (pp.41-44)Figure 2.11 Field ecosystem showing its trophic levels and simplified energy pathwaysTrophic Levels: Represent ways in which energy is obtained from the environment 10Community Organization:Food Chains and Food WebsFigure 2.12 A diagram of an actual food web studied in Gatun Lake, PanamaGuilds of competing species: Feeding at the same trophic level. 11Community Organization: Keystone SpeciesFigure 2.13 Keystone Species 12Community Organization: Keystone SpeciesKeystone species and guilds are a priority for conservation effortsLoss of keystone species leads to loss of many other speciesTop predators often considered keystone speciesCan significantly influence herbivore populationsE.g. Grey wolves and deer 13Community Organization:Keystone SpeciesImpact of some keystone species not as obvious as others2.14 Flying foxes are vital pollinators and seed dispersers in Old World tropical forest communities 14Community Organization:Keystone SpeciesEcosystem engineers are also keystone speciesExtensively modify physical environment via their activities:BEAVERSEARTHWORMSLEAF CUTTER ANTSDUNG BEETLESDISEASE CAUSING ORGANISMS AND PARASITES. 15Community Organization:Keystone SpeciesFigure 2.15 Dung beetles are important keystone species in many communities 16Community Organization:Keystone SpeciesImplications for conservation biology:Loss of keystone species precipitates losses of other speciesSeries of linked extinction events = EXTINCTION CASCADERESULTS: DEGRADED ECOSYSTEM WITH LOW BIODIVERSITY AT ALL TROPHIC LEVELSIf can identify keystone species in an environment designated for human activity, can protect these but allow harvest of other species whose reduced abundance will have less impact 17Community Organization: Keystone ResourcesOften nature reserves are compared and valued based on sizeGenerally larger reserves ? more species and habitatsMust take into account keystone resourcesSMALL PHYSICAL OR STRUCTURAL COMPONENT OF A HABITAT THAT IS CRUCIAL TO SPECIES/COMMUNITY SURVIVAL. 18Community Organization: Keystone ResourcesSalt licks and mineral poolsDISTRIBUTION OF SALT LICKS CAN DETERMINE ABUNDANCE AND DISTRUBTION OF VERTEBRATES IN AN AREADeep pools in streams and springsPROVIDE REFUGIA FOR FISH AND INVERTEBRATES SPECIES DURING DROUGHTHollow tree trunksNEEDED AS BREEDING SITES FOR MANY BIRDSSUITABLE TREE TRUNKS ARE LIMITING RESOURCES FOR MANY VERTEBRATES SPECIESRotting woodIMPORTANT IN BOTH TERRESTRIAL AND AQUATIC HABITATSBREEDING AREA AND REFUGIA FOR FISH 19Where is the World’s Biodiversity Found?Current Patterns of Species RichnessThe distribution of organisms across the earth’s surface is not uniform.There are important general patterns.Distribution patterns are best known for the temperate regions (most taxonomists and ecologist live/work here).The most species-rich environments appear to be tropical rainforests, deciduous forests, coral reefs, possibly deep sea. 20Where is the World’s Biodiversity Found?Tropical forests:Much of diversity attributed to great abundance of insectsThere are also many bird, mammal and plant speciesCoral Reefs and Deep SeaDiversity spread over broader range of phyla and classesOf 33 animal phyla that exist, 28 found in marine systems13 of these phyla exclusively marine 21Where is the World’s Biodiversity Found?Diversity in ocean may be due to:GREAT AGEVAST AREADEGREE OF ISOLATION OF CERTAIN SEAS BY INTERVENING LAND MASSESSTABILITY OF ENVIRONMENTSPECIALIZATION ON PARTICULAR SEDIMENT TYPES. 22Where is the World’s Biodiversity Found?Large Tropical Lakes: diversity accounted for by fast evolutionary radiation of fishes and other speciesHabitat is isolated and highly productiveTemperate Communities:High level of plant diversity in:Australia, Cape region of South Africa, California, Central Chile, Mediterranean basinMoist winters and hot, dry summers contribute to high plant diversity 23Where is the World’s Biodiversity Found?Why high diversity of shrub and plant communities in temperate regions?May also be due to:Geographical ageComplexity of site conditionsSevere environmental conditionsFrequency of fire – may favour rapid speciation 24Patterns of DiversityPatterns of species richness affected by:Local variation in climateEnvironmentTopographyGeological age 25Patterns of DiversityVariations in Climate and Environment:Terrestrial communities:Richness increases with:decreasing elevationIncreasing solar radiationIncreasing precipitationThese factors act in combinationDeserts are species poor – low precipitation even though have high solar radiationIn some areas, greatest species abundance occurs at mid-elevations 26Patterns of DiversityVariations in Topography, Geological Age and Habitat Size:Species richness greater where have complex topography and great geological ageProvides more environmental variation allowing more genetic isolation, local adaptation and eventually speciationE.g. mountain peaksLarge drainage systemsSoil conditions 27Patterns of DiversityLarger areas can provide greater range of habitats in which species can evolveFigure 3.4 Global distribution of the coral reef biome 28Patterns of EndemismA species that is found in a particular region but nowhere else is endemic to that region.Regions with many endemic species are the result of one or more major events caused geographic isolation.Causes of geographic isolation:CONTINENTAL DRIFTFORMATION OF MOUNTAINSCLIMATE CHANGE [geological time, over many years]CHANGES IN SEA LEVEL [geological time, over many years] 29Patterns of Endemism 30Patterns of EndemismContinental drift has been very important in generating high levels of endemism in Madagascar, Australia, New Guinea, New Caledonia.Islands also have high levels of endemism because they are isolated but often species richness is low.Coral reefs however have both a high level of endemism and high species richness. 31Patterns of EndemismPatterns of endemism also vary among taxa.There are many endemic plants but few endemic mammals or birds.Polyploidy is common in plants and allows them to speciate in smaller areas.Polyploidy is rare in vertebrates. 32Why So Many Species in the Tropics?In both marine and terrestrial habitats, lower latitudes support more species than higher latitudes.Figure 3.5 In North America numbers of bird, tree, and mammal species increase toward the Tropics 33Why So Many Species in the Tropics?This pattern in terrestrial systems also mirrored in marine systemsE.g. Great Barrier Reef (Australia)Northern end (approaching the tropics) has 50 genera of reef-building coralSouthern end (farthest from tropics) has only 10 genera of reef-building coral 34Why So Many Species in the Tropics?Many plausible theories to explain this:Tropical regions receive more solar energy over the year than temperate regionsRESULTS IN HIGHER RATE OF PRODUCTIVITYTHEREFORE HIGHER RESOURECES BASE THAT CAN SUPPORT WIDER RANGE OF SPECIESLarger geographical areaLARGE AREA MAY COOUNT FOR GREATER SPECIATION RATES AND LOWER EXTINCTION RATES 35Why So Many Species in the Tropics?Tropical communities have had longer periods of stability than temperate communitiesTEMPERATE AREAS HAVE HAD TO DISPERSE IN RESPONSE TO GLACATION (SCOURING COLD CLIMATE)GREATER STABILITY IN TROPICS ALLOWS EVOLUTION AND SPECIATION TO OCCUR UNINTEREUPTEDGREATER DEGREE OF SPECIALIZATION AND LOCATION ADAPTIONWarm temperature and high humidityIN TROPICS THEESE CONDITION FAVOUR GROWTH AND SURVIVAL OF MANY SPECIESENTIRE COMMUNATIONS CAN ALSO DEVELOP IN TREE CANOPIES 36Why So Many Species in the Tropics?Intense species interactionsDUE TO PREDICTABLE TROPICAL ENVIRONMENT, HAVE GREATER COMPETIION AND EVENTUALLY NICHE SPECIALIZATIONALSO GREATER PRESSURE FROM PARASITES AND DISEASE (NO FREEZING TEMPERATURES TO KEEP THESE IN CHECK) PREVENTS ANY ONE TROPICAL SPECIES FROM DOMINATIONG IN A COMMUNITYRESULTS ? MANY SPECIES COEXIST AT LOW DENSITY. 37Exceptions:There are a few organisms that don’t adhere to the latitudinal gradient pattern.Seaweeds show no consistent pattern with latitude.Parasites, parasitoid wasps and aquatic plants also seem to be exceptions.Marine birds and mammals have greater species richness at high latitudes.The reason for this is not clear. 38Recently Discovered CommunitiesEntire communities continue to be discovered, often in very remote/inaccessible areas:Tropical tree canopies 39Recently Discovered CommunitiesBACTERIA AND ANIMALS IN GEOTHERMAL VENTS (BOX 3.1 – REQUIRED READING)Box 3.1 Part of a hydrothermal vent community 40Recently Discovered CommunitiesFungi living in healthy tropical tree leavesSample of 83 leaves ? 340 distinct species of fungiFungi help plant to exclude harmful bacteria and fungiGood fungi get a place to live and some carbohydrates in return