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Lecture 16

BIOC63Fall2013 Lecture 16.docx

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Biological Sciences
Karen Williams

BIOC63Fall2013 Lecture 16 Populations and how they behave Metapopulation vs. source-sink dynamics  Longevity of habitats  Source-Sink = long lived  MetaPop: often short lived  MP: several distinct populaions along with areas of suitable, but unoccupied habitats  Populations eventually go extinct, and are then repopulated  In both models, migration is key!   High quality habitats produce extra amounts of individuals that can be supported in the lower quality habitats  Sinks are supported by sources  Species move around in space and time  Some of the good pathces remain undiscovered Example of metapopulation dynamics  Insect feeds on decaying tree  some decaying trees are not discovered = some good habitats are not discovered Metapopulation dynamics and diversity  Finland  plantations of aspen wood for paper production  NE Russia  this portion of Russia is underdeveloped so it looks more natural (young, old and ‘broken’ trees)  Presence of rare insects  rarity classes of insects with reference to Finland  V = vulnerable, R = rare, E = endangered, Ex = extirpated  In habitat where there are very few logs (Finland) it is harder for insect to find suitable habitat, but they can find natural habitat in Russia  more rare species of insects found in NE Russia than in Finland 1  General metapopulation dynamics in forests  mosaic of different age (and therefore light) classes Spring ephemerals and light  they need a lot of light because they create their seeds in the spring   1 = colonization (seed)  2 = growth and persistence  3 = fitness decline  4 = local extirpation  as light levels decrease, the population will start to decrease which can lead to extirpation Metapopulation dynamics in cowslip 2   Pop growth rate of 1 means no change in population  The more open the canopy, the greater the population growth rate of cowslip  Where the sun is = just after gap creation few adults (because gap creation just ocurred), lot sof seedlings  As they move forward in time, light levels sink  The maturity of the population increases  seedlings become adults that produe their own seedlings  Become old established adults  too dark for the younger generations to produce more seedlings, so the population starts moving towards extirpation Metapopulation dynamics and conservation  Landscapes are naturally dynamic  For conservation, keep/reinstall dynamics  Protect more habitat than just the space where populations are currently located (because they move) Human fire suppression  Many (semi)-open habitats are disappearing: black-oak savannahs(ON) and alvars (ON)  Oak savanna  in the pst in ON places contained these black oak savannas  but because we are supressing fire, these landscapes are overgrown  Alvars = nutrient poor, so high diversity  fire cycle here is much much shorter, so they are kept open because fire removes this  But when we supress this, the alvars now grow to a closed ecosystem which leads to extirpation of many species  Flood suppression  many semi open habitats are disappearing = floodplain forests and mud plains 3   Rivers look like this today because they are kept in the river beds by dams so they do not flood  Which allows for growth of forest = appearing as dark green Population persistence assessments Minimum viable population (MVP)  Def: smallest possible size at whch a populationcan exist without facing extinction from various factors (chance events)  MVP needs to be large enough to be able to buffer small and greater catastrophies  Chance events affecting small populations:  Density independent catastrophies, resource fluctuations  DD factors: pests, herbivory  DD factors: genetic drift and inbreeding  DD factors: demographic stochasticity: sex ratio and age structure MVP size  102 vertebrate species distributed worldwide  mean MVP: appro
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