Lecture 6

1Conservation BiologyBIOL3620Lecture 6Estimating Extinction and Vulnerability to ExtinctionPrimack Chapters 7 and 8Please submit Assignment 1 2Estimating Extinction RatesThe Island Biogeography Model (MacArthur and Wilson, 1967)General rules on distribution of biodiversitySame model can be used to estimate future extinction ratesCentral observation that model explains: species-area relationship 3Estimating Extinction RatesFigure 7.8 The number of species on an island can be predicted from the area of an island 4Estimating Extinction RatesWhy do large island support more species?1. GREATER VARIETY OF LOCAL ENVIRONMENTS AND COMMUNITY TYPES2. ALLOW GREATER GEOGRAPHICAL ISOLATION3. SUPPORT LARGER NUMBER OF POPULATIONS/SPECIES4. SUPPORT LARGER SIZES OF INDIVIDUAL POPULATIONS5. INCREASED LIKELIHOOD OF SPECIATIONS6. DECREASED PROBABILITY OF LOCAL EXTINCTION OF NEWLY EVOLVED SPECIES AND RECENTLY ARRIVED SPECIES. Estimating Extinction RatesSpecies-area relationship can be described by:5S (# OF SPECIES ON ISLAND) = C(ONSTANT)A(REA OF ISLAND)Z (DETERMINES SLOPEZ values range from 0.15 – 0.35; typically around 0.25REPTILES, AMPHIBIANS WITH RESTRICTED RANGES: Z = 0.35WIDESPREAD MAINLAND SPECIES: Z=0.15C values:HIGH FOR GROUPS HIGH IS SPECIES NUMBERS (INSECTS)LOW FOR GROUPS LOW IN SPECIES NUMBERS (BIRDS) 6Estimating Extinction RatesModel validated and accepted by most biologists for most groups of plant and animalsExample: Anolis lizard speciesC = 0.25Z = 0.35Island and areaPredicted # speciesActual # speciesSt. Nevis – 93 km222Puerto Rico – 8959 km21210Cuba – 114,524 km23057 7Estimating Extinction RatesIsland biogeography hypothesis:1. Number of species on an island represents dynamic equilibrium between arrival of new species (also evolution of new species) and extinction rate of existing speciesOn unoccupied island, number of species will increase over time since more species are arriving (or evolving) than going extinctContinues until rates of extinction and immigration are balanced 8Estimating Extinction RatesIsland biogeography hypothesis:2. Immigration rates higher on large vs. small islandsLarge islands:LARGER TARGET FOR DISPERSING SPECIESMORE SUITABLE OPEN HABITAT FOR COLONIZATION3. Extinction rate lower on large islandsLarge islands:GREATER HABITAT DIVERSITYGREATER NUMBER OF POPULATIONS4. Immigration rates of new species higher for islands near mainland vs. those further from mainland 9Estimating Extinction RatesFigure 7.9 The island biogeography modelIMMIGRATION RATEEXTINCTION RATE 10Extinction Rates and Habitat LossUse of Species-area relationships:to predict number and percentage of species that would become extinct if habitats were destroyedAssumption:Given a certain number of species on an island, reducing the area of natural habitat results in island being able to support only a number of species corresponding to that on a smaller islandUseful model for national parks and nature reserves surrounded by degraded habitatReserves = “habitat islands” 11Extinction Rates and Habitat LossModel predictions:7.10 According to the island biogeography model, the number of species present in an area increases asymptotically to a maximum valueImportant note:Shape of curve is different for each region of world and each group of species, but model still useful as predictor of effect of habitat destruction on species extinctions 12Extinction Rates and Habitat LossExample:Singapore: 95% of originalforest cover lost over last 180 yearsModel estimates: 30% lossof forest speciesActual: 32% loss of nativebird species from 1923 – 1998Greater losses of large ground birds and insectivorous birds of forest canopy 13Extinction Rates and Habitat LossExtinction rate predictions based on habitat loss vary greatlyEach species-area relationship is uniqueBecause insects and plants in tropical forests account for large proportion of species in the world – often used for estimates of global extinction ratesConservative estimate:1% loss of world’s rainforest per yearEstimates 0.2-0.3% species lossIf use 5 million species worldwide = 10,000 – 15,000 species per year (34 species per day) 14Assumptions and Generalizations of Island Biogeography ModelAssumptions and generalizations of extinction rate predictions using model:Based on typical values for species-area curvesSpecies with broad geographical ranges (marine mammals, temperate tree species) have lower extinction rates Species with narrow ranges (island birds, freshwater fish) have higher extinction ratesModel assumes all endemic species eliminated from large, cleared areasPossible that species can survive in isolated patches or adapt to plantations and managed forests 15Assumptions and Generalizations of Island Biogeography ModelModel assumes areas of habitat are randomly eliminatedSpecies rich areas often targeted for conservation, so greater species may be protected than assumed by modelDegree of habitat fragmentation may affect extinction ratesVery small patches cannot maintain large populationsHunting, clearing for agriculture, introduced species in fragmented areas may lead to further losses 16Other MethodsExtinction rates can be estimated using information on:PROJECTED HABITAT DECLINESNUMBERS OF POPULATRIONSGEOGRAPHICAL RANGE WELL KNOWN SPECIESAdvantages:Uses empirical information for more accurate estimate of extinction rates for smaller number of speciesEstimates closely approximate those using island biogeography method applied to specific geographical area 17Other MethodsEstimates of when extinctions will occur:Cannot be done with island biogeography methodCan compare predictions with historical examples to give estimate of time frame of extinctionE.g. Bird species in forest fragments in Kenya½ OF BIRDS LOST 50 YEARS ? 1000 KM½ OF BIRDS LOST 100 YEARS -> 10,000 KM 18“Local Extinctions”- ExtirpationsExtirpations are also a primary focus of conservation biologyMany species experiencing extirpations due to habitat degradation, destructionFormerly widespread species reduced to small pockets of former habitatE.g. Nicrophorus americanus (American burying beetle 19Local Extinctions7.11 The American burying beetle is now found only in four isolated populations 20Vulnerability to ExtinctionNot all species have equal chance of going extinctSome species more vulnerable to extinction than others, for example:Rare speciesEndemic species 21Vulnerability to Extinction –Rare SpeciesRare SpeciesCriteria for rarity:1. NARROW GEOGRAPHICAL RANGES2. SPECIFIC HABITAT REQUIREMENTS3. SMALL POPULATION SIZES1. Narrow Geographical RangeVenus’s-flytrap – rare because occurs only in certain areas but,Rare species may be locally abundant within limited geographical range 22Vulnerability to Extinction –Rare SpeciesSpecies can also be geographical rare in only part of their rangeE.g. Sweet Bay MagnoliaFOUND IN THE USRARE IN NEW ENGLANDRare species may havealways had a narrowgeographical range orMay have been more widespread and become restricted due to human activities = artificially rare 23Vulnerability to Extinction –Rare Species2. Specific habitat requirements:Species considered rare if occupies one or a few specialized habitatsE.g. Salt marsh cord grassONLY FOUND IN SALT MARSHESHOWEVER, IT IS QUITE COMMON IN THIS HABITAT 24Vulnerability to Extinction –Rare Species3. Small populationsSpecies considered rare found only in small populations although the populations are found over a wide areaRare because populations are small and isolatedE.g. Mediterranean monk seals 25Vulnerability to Extinction –Rare SpeciesThe criteria of rarity can be applied:To entire range of species, orTo distribution and abundance of species in a particular placeUsed to highlight priorities for conservationSpecies that fit all three criteria require immediate habitat protection and possibly management to maintain existing populationsSpecies with narrow geographical distribution but broad habitat specificity, may benefit from translocation 26Vulnerability to Extinction - EndemicsEndemic Species and ExtinctionEndemic species = naturally found in a single geographical area and nowhere else in the worldA species may be endemic to a large area and very abundant in that areaCompare to rare species - only found in a limited areaEndemic species very important in species’ risk of extinctionOnce extinct in one area it is globally extinct 27Vulnerability to Extinction - EndemicsEndemic Species and ExtinctionSome species occupy small area because have recently evolved from closely related species = neoendemicsE.g. Hundreds of species ofcichlid fish in Lake Victoria, E. AfricaPaleoendemics are ancient species whose close relatives have all gone extinctE.g. Giant pandas, coelacanths 28Vulnerability to ExtinctionWhere are Endemic Species Found?Isolated geographical units:Remote islandsOld lakesSolitary mountain peaksGeologically old continental areas with Mediterranean climatesSouth AfricaCaliforniaHawaii 29Species Most Vulnerable to ExtinctionFive categories of species most vulnerable to extinction:Species with very narrow geographical rangeIf entire range is affected by human activity, species may become extinctBIRDS ON OCEANIC ISLAND HAVE RESTRICTED RANGESFISH SPECIES CONFINED TO A SINGLE LAKE OR WATERSHED (I.E. DESERT PUPFISH)SPECIES WITH LIMITED RANGES AND VULNERABLE TO GLOBAL CLIMATE CHANGESpecies with one or a few populationsExtinction may occur due to chance (earthquake, flood, fire, disease or human activity)Also linked to abovestyle.visibility 30Species Most Vulnerable to ExtinctionFive categories of species most vulnerable to extinction:Species with small population sizes“small population paradigm”SMALL POPULATIONS MORE LIKELY TO GO LOCALLY EXTINCT BECAUSE MORE VULNERABLE TO:DEMOGRAPHIC AND ENVIRONMENT VARIATIONLOSS OF GENETIC VARIABILITYSpecies with declining population sizesUSUALLY POPULATION IN DECLINE CONTINUE UNLESS CAUSE OF DECLINE INDENTIFICED AND CORRECTED 31Species Most Vulnerable to ExtinctionFive categories of species most vulnerable to extinction:Species that are hunted or harvested by peopleIF THE SPECIES IS OVERHARVESTED, THIS MAY CAUSE EXTINCTIONHUNTING AND HARVESTING MUST BE REGULATED. 32Species Most Vulnerable to ExtinctionOther categories that may lead to decline in certain cases:Species requiring large home rangesAnimals with large body sizeHAVE LARGE INDIVIDUAL RANGES, LOW REPRODUCTIVE RATES, MORE EXTENSIVE FOOD REQUIREMENTS, MORE OFTEN HUNTED BY HUMANSLONGER LIFE SPANS OF THESE ANIMALS SOMETIMES HELP TO COUNTER EFFECTSSpecies that are poor dispersersCANNOT EVADE CHANGING ENVIRONMENTS 33Species Most Vulnerable to ExtinctionOther categories that may lead to decline in certain cases:Seasonal migrantsDEPEND ON TWO OR MORE DISTINCT HABITAT TYPESSpecies with little genetic variabilitySpecies with specialized niche requirementsONCE A HABITAT IS ALTERED, THE NEW CONDITIONS WILL NOT BE SUITABLE FOR THOSE SPECIES HIGHLY SPECIALIZED TO A SPECIFIC NICHESpecies found in stable, pristine environmentsMINIMAL DISTURBANCE IN THESE ENVIRONEMNTS, CHANGES NOT TOLERATED 34Species Most Vulnerable to ExtinctionOther categories that may lead to decline in certain cases:Species forming temporary or permanent aggregationsCAN BE EASILY HARVESTEDAllee effect – if population falls below certain number cannot forage, find mates, defend themselves (e.g. social insects)Species with no prior contact with humansSpecies with closely related species that are recently extinct or are threatened with extinction. 35Conservation CategoriesConservation biologists must identify those species most vulnerable to extinctionInternational Union for the Conservation of Nature (IUCN) has established nine conservation categoriesWithin the nine categories there are three primary categories:CR – CRITICALLY ENDANGEREDEN – ENDANGEREDVU – VULNERABLEThese three categories are all considered threatened with extinction 36Conservation CategoriesThe categories are also important at national and international levelsUsed for publication of Red Data Books and Red Lists of threatened speciesAlso useful for identifying species of special concern and identifying threatened species for protection through international agreements such as CITES – (Convention on International Trade in Endangered Species) 37Conservation CategoriesFigure 8.4 The IUCN categories of conservation statusOn national and regional level also have:Regionally extinct (RE)Not Applicable (NA) – refers to introducedspecies or rare migrants 38Conservation CategoriesThe categories:Extinct (EX) – no longer exitstsExtinct in Wild (EW) – exists only in cultivation, in captivity or as naturalized population outside of rangeCritically Endangered (CR) – extremely high risk of going extinct in wild according to IUCN Red List criteriaEndangered (EN) – very high risk of extinction in wild according to IUCN Red List criteria 39Conservation CategoriesThe categories:Vulnerable (VU) – high risk of extinction in wild according to IUCN Red List criteriaNear Threatened (NT) – close to qualifying for threatened category but not yet considered threatenedLeast Concern (LC) – Widespread and abundantData Deficient (DD)Not Evaluated (NE) 40Conservation CategoriesHow are the categories assigned?Must have at least one of the following types of informationMust be able to compare that data to threshold values given by IUCN Red List CriteriaA. OBSERABLE REDUCTION IN NUMBERS OF INDIVIDUALSB. TOTAL GEOGRAPHICAL AREA OCCUPIED BY SPECIESC. PREDICTED DECLINE IN NUMBER OF INDIVIDUALSD. NUMBER OF MATURE INDIVIDUALS CURRENTLY ALIVEE. PROBABILITY OF SPECIES GOING EXTINCT IN CERTAIN NUMBER OF YEARS OR DECADES. 41Conservation CategoriesHow are the categories assigned?Assignment of categories based on population viability analysisPopulation trendsHabitat conditionUseful for those species for which there is little biological informationCan be listed based on their habitat being destroyed 42Conservation CategoriesExample:A critically endangered species has at least one of the following characteristics:80% population decline in last 10 years or 3 generations – Criteria ASpecies has restricted range – 100 km2 or less at single location – Criteria BCan be observed or predicted habitat lossTotal population less than 250 mature, breeding individuals and expected to decline by 25% within 3 years or 1 generation – Criteria CPopulation size less than 50 mature individuals – Criteria DOverall extinction probability > 50% in 10 years or 3 generations – Criteria E 43Conservation CategoriesAdvantages of this method:PROVIDES STANDRD, QUANTITATIVE METHOD OF CLASSIFICATION USING AVAILBLE DATACAN BE REVIEWED AND EVALUATED BY OTHER SCIENTISTS AND CRITIQUEDDisadvantages:ASSIGNMENT CAN BECOME QRBITRARY IF THERE IS INSUFFICIENT DATAGATHERING DATA EXPENSIVE AND TIME-CONSUMINGESPECIALLY FOR DEVELOPING COUNTRIES 44Conservation CategoriesIUCN system used to highlight conservation prioritiesApplied to specific geographical areas and groups 45Conservation Categories 46Conservation Categories 47Conservation CategoriesIUNC Red ListLiving Planet Index 48Natural Heritage Data CentresNatureServe networkNatureServe Canada