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University of Toronto St. George
Doug Thomson

LECTURE 8: Metapopulations, plant community compositions  Nature occurs in patches  Fender’s Blue butterfly depends on one particular plant → Kincaid’s Lupine – Only lays eggs on these plants where caterpillars grow up feeding on it – Only exists on prairie patches  Only exist on prairie patches or die without reproducing  Larger patches can support a population since when they disperse they’d still end up in the area within the patch  Smaller ones go extinct – migration out of patch to agriculture patches without the Kincaid’s Lupine  Small patches near larger ones can sustain due to migration  All depends on quality, size and proximity of patches as well as dispersal  Populations are not easily driven to extinction due to non-equilibrium conditions – Certain species can manage in a certain patch – Migration – Patterns of dispersal (R and K species)  R species – weedy plants good at dispersal with high reproduction rate → semelparous  K species - more investment in somatic growth, shade tolerant, slow growth → iteroperous  Metapopulation theory – if death rate = migration rate then the metapopulation will exist indefinitely  Andy Smith – distribution of Pika metapopulations – lives in patches (north, middle, south) – North: high, stable population due to large stable patches – Middle: ups and downs, can’t sustain very well – South: decline of Pikas  Source – disperses population to other places  Sink – population that depends on the import and migration of Pikas  Clement – species association where a particular pair of species occur in the same piece of vegetation and has a functional relationship with each other – biotic factors  Gleason – species are individualistic, does not depend on one another. They are found near each other because they have the same range of tolerance (abiotic conditions & dispersal) – abiotic factors  Gradient analysis – Curtis (indirect) & Whittaker (direct) – Davis – used pollen data to reconstruct post-glacial migrations of trees – did not move in clusters – Proved that each plant is an entity to itself – individualistic  Animal communities are less individualistic than plant communities Lecture 9: Spatial Ecology, Plant Communities, and Disturbance  Succession – change of plants through time in a predictable sequence  Soil development and shading is critical  Vegetation changes spontaneously, independent from humans  Classic view of succession: – Starts with pioneer species (R-species – weedy perennials) – Goes through temporary equilibrium stages – Ends at climax, stable equilibrium – no more changes (K- species – competitive, shade tolerant )  Primary succession – new habitat created with no prior vegetation due to large disturbances where all living individuals and nutrients in soil were removed (volcanic activity, sand dunes, retreating glaciers…)  Secondary succession – disturbance of pre-existing vegetation (abiotic disturbances, fire, agriculture…) – Can quickly re-colonize the areas of disturbance – Perennial weeds with seeds in the soil germinate when conditions are wet enough – Dispersal of plants colonize the area – slowly develop woody trees – species are replaced – Shading becomes a factor – taller plants out compete lower plants – Eventually reach a climax with K-species which are shade tolerant and replaces itself  Soil development becomes more complex and organic  Shading starts to occur when there’s many layers of foliage in developing forests  Clement – concept of climax communities – permanent stage of succession after any disturbances any ecosystem will return to its characteristic assemblage of species – Super organism concept – working together to maintain a stable composure  Not all vegetation will get to a climax stage – some will never achieve it – Boreal forest: spruce-fir does not replace itself due to too much shade, makes soil acidic, more combustible than tropics resulting in fires – Fire dominant communities have no stable climax and no shade tolerant species  Ground fires – not that harmful to trees with thick barks good for regrowth  Crown fire – more harmful – allows seeds in pine cones to disperse  Organisms adapt to a pattern of burning  Gleason – communities were individualistic, changes are not as predictable as Clement proposes – Species diversity increases with successional age – Early successional plants have higher rates of photosynthesis & respiration, resource up take and light compensation points  Habitats are in mosaic patches of different stage of regrowth after disturbance  ‘gap phase succession’ – when gaps are created for new pioneer species to develop – Occurs through fire (dry forests) or in tropics when large trees fall over to allow new pioneer species to inhabit the gaps – promotes more diversity  Facilitation succession – early successional species modify environment for later species to replace them  Tolerance succession – later successional species are more long lived and replace earlier species  Inhibition model – early colonists dominate until a disturbance removes them and longer lived species replace them  Change of ratio of resources overtime can shift community composition  Chronosequence of sand dunes – bare sand, beach, grasslands, mature forest Lecture 10: Trophic Relationship in Communities  Primary produces – plants, primary consumers – herbivores, secondary consumers – carnivores who eat herbivores, tertiary consumers – carnivores who eat secondary consumers, and those who eat organic matter  Insecticide treatment to plants that removes beetles lowers plant diversity  Trophic cascades – carnivores limit herbivores so they don’t limit plant growth – Indirect effect – one trophic level exerts on influence of second by affecting a third – Outcomes are not predictable – depends on interaction strength, less drastic in large populations  Keystone species – species with a large effect on its environment relative to its abundance  Carnivores –animal tissues easily convert to animal tissues  Herbivores – plant tissues are hard to convert to animal tissues – Many plant materials are indigestible (cellulose & lignin tough) – Developed enzymes to break down plant material – Plants have any defenses against herbivores – Vivid colouring on herbivores warn predators of its toxicity  Graminoids (grasses) contain crystals to grind molars of herbivores consuming it – mechanical defense  Mammalian herbivores have grazing teeth to adapt to the graminoids  Coevolution arms race – plants and herbivores become more and more better defended each other – promotes evolution and more biodiversity  Less seasonality in rainforests lead to higher diversity  Janzen Connel – rain of death – seedlings have a low chance of survival within the vicinity of the mother plant because bugs inhabiting the mother plant would consume it – Higher survivability rate further away from the mother plant  Pikas manipulate toxin levels of toxic plants by preserving the over winter and eats the when its less toxic Lecture 11: Species Interactions in Subalpine Meadows  Research on “Glacier Lilies” – grow best where surface soil is rocky – Iteroperous plant – flowers more than once during its life time – vegetative state for many years before flowering – Has a corm underground to keep resources during winter – Poor dispersal of seeds from the parent plant  Some plants have secondary dispersal by ants – they eat elaiosomes surrounding the seed leaving the seeds underground to grow (not for these plants)  Seedlings in deep soil areas are away from where the abundance of plants are (in rocky areas)  No correlation between flowers and seedlings  Gopher predation in moist organic soil so they would eat the seedlings before they reach flowering age – Rock refuge hypothesis – staying near the parent habitat is more beneficial than seeking moist organic soil so dispersal is disadvantageous – Reason why these plants don’t have elaiosomes  Gopher predation also occurs in roots of aspens – prevents aspens from spreading into the meadows – Rock refuge effect – aspens grow on rocky soil but it keeps the spatial patchiness – Allows Glacier Lilies to grow in meadows  Green house gases keeps the sun’s heat energy within the plant atmosphere  The more greenhouse gases the higher the temperature – As atmosphere warms, it contains more water – Changes circulation patterns of Hadley cells – descend dry air around 30 degrees however if greenhouse emissions continue, the large belts will shift beyond 30  Affect organism – they will move up higher latitudes and altitudes to a cooler climate  Those already at high latitudes (Pikas and polar bears) will have nowhere to go – Polar bears may migrate south and disappear through hybridizat
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