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Lecture 5

American University - Washington D.C.
Uploaded: 7 years ago
Contributor: Eels
Category: Conservation Biology
Type: Lecture Notes
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Filename:   Lecture 5.pptx (2.23 MB)
Credit Cost: 3
Views: 259
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Transcript
1Conservation BiologyBIOL3620Lecture 5 Threats to Biodiversity - ExtinctionPrimack, Chapter 7 2Present geological time has more species than any otherBut current extinction rate is greater now than any time in the pastEcosystems/communities degraded and destroyedSpecies driven to extinctionGenetic variation in persisting species being lostPopulations becoming increasingly isolatedExtinction 3Presently, 40-55% of NPP (NET PRIMARY PRODUCTIVITITY: RATE AT WHICH CARBON IS INCORPORATED INTO PLANTS – TRANSLATES INTO PLANT GROWTH, SIGNIFICANT BECAUSE IT IS A MEASURE OF THE AMOUNT OF ORGANIC MATTER FROM BY AUTOTROPHS AVAILABLE TO HETEROTROPHS) of terrestrial environment (representing 25% of total global primary productivity) is used or wasted by humansGenetic variation even being lost in domestic speciesIn tropical countries, farmers are abandoning local plant/vegetable varieties for high-yield varietiesLoss of variability among food plants and animals ? serious implications for world agriculture 97 PERCENT OF THE VARIETIES ONCE CULTIVATED ARE NOW EXTINCTExtinction 4E.O. WilsonExtinction of species of greatest importanceBiological communities can be degraded, reduced in area, devalued to people ? as long as original species survive there is potential for recoverySame applies to genetic variationChance for recovery if genes persistOnce DNA gone, population cannot be restoredExtinction 5Definition can vary depending on contextTypes of extinctions:Global extinctionExtinctExtinct in the wildLocal extinction or extirpationRegional extinctionEcological extinctionAll types cause shifts in: COMMUNITY COMPOSITION ECOSYSTEM STRUCTURE AND FUNCTIONWhat is Extinction? 6Global extinctionExtinct means that no member of the species remains alive anywhere in the worldMost tragicUsually due to human activitiesEg. Bachman’s Warbler (Vermivora bachmanii)What is Extinction? 7What is Extinction?Bachman’s warbler – last seen in the 1960’sExtinctFigure 7.1 Bachman’s warbler became extinct as a result of tropical deforestation in its wintering grounds 8What is Extinction?Global extinction also includes extinct in the wildINDIVIDUALS OF THE SPECIES REMAIN ALIVE ONLY IN CAPTIVITY OR OTHER HUMAN-CONTROLLED CONDITIONI.E. FRANKLIN TREEEg. Franklin tree (Franklinia altamaha) 9Local extinction or extirpationLOSS OF SPECIES FROM ONE SITE OR REGION BUT STILL FOUND ELSEWHEREI.E. GREY WOLF (FOUND IN CANADA, US.)Eg. Grey Wolf (Canis lupus)What is Extinction? 10What is Extinction?Regional extinctionEXTINCT IN A COUNTRY OR REGION, BUT STILL PERSISTS IN ANOTHER PART OF ITS RANGESmall Blue Cupido minimus 11Ecological extinctionPOPULATION REDUCED DRASTICALLY SUCH THAT ITS EFFECTS ON OTHER SPECIES IN COMMUNITY ARE NEGLIBIBLEEg. Tigers (Panthera tigris)What is Extinction? 12Species diversity on Earth has been increasing since origin of lifeIncrease characterized by:Periods of high speciation rates followed by periods of minimal changeEpisodes of mass extinctionsPattern very evident in the fossil recordPast Mass Extinctions 13Past Mass Extinctions7.2 The number of families of marine organisms has been increasing over geological timeOccurrence rate of new families: one/million yrs 14Past Mass Extinctions7.3 During each of five episodes of natural mass extinction a large percentage of gradually increasing groups disappeared 15Anthropogenic extinctions have direct and indirect causes:Direct – OVEREXTRAPOLATIONIndirect – HABIBTAT TRANSFORMATIONSRestrict population size/species growthIntroduction of new speciesAnthropogenic Extinctions 16Earliest human-caused extinctions due to:OverexploitationLater – habitat modifications, invasive species introduction.Most recently – disease, pollution, anthro-pogenic global climate change.Future – synergistic effects with climate change.Anthropogenic Extinctions 17Difficult to monitor extinction events due to prehistoric humans - incomplete fossil records.One notable event:Pleistocene extinction of megafauna and other vertebrates (IMPORTANT).Megafauna = MAMMALS, BIRDS, REPTILES OVER 44 KG.72%-88% of large mammal genera went extinct in Australia, North America, Mesoamerica and South America with arrival of humans.Anthropogenic Extinctions 18Anthropogenic Extinctions 19Timeframe for this extinction:Australia (44,000 – 72,000 years ago).North and South America (10,000 – 15,000 years ago).Probable direct cause of extinctions: huntingProbable indirect causes: burning and clearing of grasslands and forests.Important to note that in some areas (Alaska and Northern Asia) rapid climate change and change in vegetation also took place. This probably played a greater role in these areas (low human population) than human influenceAnthropogenic Extinctions 20Extinction rates during the last 2000 years best known for terrestrial vertebrates (especially birds and mammals)More conspicuousWell studiedEven for these groups, extinction rates are uncertainSome species thought to be extinct have been rediscoveredAnthropogenic Extinctions 21Australian night parrotLAST SEEN 1912REDISCOVERED 1979North American Ivory BilledWoodpeckerPRESUMED EXTINCT FOR DECADESREDISCOVERED IN 2005Also keep in mind that manyspecies presumed extant, may be extinctAnthropogenic Extinctions 22 23Extinctions since the year 1600:77 species of mammals (1.6% of all mammal species)129 species of birds (1.3% of all bird species)Doesn’t seem so badKeep in mind, the trend continuesMost extinctions have occurred in the last 150 yearsAnthropogenic Extinctions 24Recent Anthropogenic Extinctions7.4 Rate of extinctions of birds during 25 year intervals since 1500 25Recent Anthropogenic ExtinctionsA species is technically not extinct even if there are only a few isolated individuals remaining in the wildAs long as they exist, even if population is no longer reproductively viable – considered not extinctBut existence is limited to lifespans of the individuals remainingRelaxation = LOSS OF SPECIES OVER TIME IN HABITAT FRAGMENTSExtinction debt = PREDICTED EVENTUAL LOSS OF SPECIES AFTER HABIBTIAT DESTRUCTION/FRAGMENTATION 26Recent Anthropogenic ExtinctionsFigure 7.5 The critically endangered cactus Melocactus actinacanthus 27 28Is Extinction Really an Issue?Extinction estimated to remain high into the next decadeIn past geological time, extinction balanced or exceeded by evolution of new speciesPresently extinction rate exceeds known evolutionary rateRecent known examples of faster than average evolutionary rate, do not produce new families or ordersHundreds of thousands or millions of years needed for evolution of new families, orders 29Background Extinction RatesNatural background extinction rates predicted from fossil record:Individual species lasts 1-10 million years before extinction or evolution into new speciesIf estimate 10 million species on Earth today, based on background extinction rate, natural extinction = 0.0001 – 0.00001% per yearCurrent rate of extinction of birds and mammals = 1% per century (0.01% per year)100 to 1000x greater than predicted natural rates 30Background Extinction RatesFor example:100 species of birds/mammals went extinct between 1850 and 1950Predicted natural rate of extinction during this time period would have been 1 species99 species extinctions can be attributed to other factors (i.e. human activity)Valid??Using even more conservative methods for calculation still comes up with extinction rate 36-78 times the background rate 31Extinction Rates on IslandsHighest rates of extinctions historically occur on islands.Polynesian colonization of the Pacific islands (1000 – 3000 years ago):over 2000 species and 8000 populations of birds driven to extinction.In some cases extinction occurred within the first 100 years after the island had been colonized. 32Why High Extinction Rates on Islands?Islands have:LIMITED AREASMALL POPULATION SIZESSMALL NUMBER OF POPULATIONSMORE ENDEMIC SPECIESIsland species usually evolve with:LIMITED COMPETITORSLIMITED PREDITORSLIMITED DISEASES 33Why High Extinction Rates on Islands?When predators introduced from mainland or if habitat degraded/destroyed, island species cannot copeHave not evolved appropriate defenses orAre eliminated by human activity extinction rates peak after humans occupy and island and then decline after elimination of most vulnerable species 34Why High Extinction Rates on Islands? 35Extinction Rates in WaterNot much research on this compared to terrestrial systemsTwelve marine species have gone extinct in past few thousand years:3 marine mammals5 marine birds4 mollusksDoesn’t seem significant but must consider their nicheE.g. many marine mammals are top predators 36Cascade Effects and ExtinctionsWhenever species depend on interactions with other species, extinction can have ripple effects.Often see secondary extinctions.Most often occur when species rely on a single or a few species as prey or as critical mutualists.Depletion of top predators may cause ecological release of prey which in turn drives down prey populations. 37Cascade Effects and ExtinctionsHelpful to determine which species are most critical – not so easy in practice.Dominant species:Very commonHave strong effects on other members of the community.Eg. Reef building corals, forest trees, large herbivores (deer). 38Cascade Effects and ExtinctionsEcosystem engineers – absence/presence will greatly effect communities.Eg. Beavers, elephantsEcosystem engineers are also considered keystone species. 39Cascade Effects and ExtinctionsKeystone species – have greater impact than would expect considering overall numbers or biomass.If a particular organism fills a niche that no other can, then it is considered a keystone species.Dominant species often easy to identify – not so for keystone species.Very often keystone species are not recognized until their numbers have been reduced and the impacts they have on other species becomes obvious.

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