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Biology 2483A
Mark Moscicki

Ecology-Lecture 3 Sept 19 2013 Biosphere  Zone of life on earth  What the world is made up of biologically Biomes  There are many systems in the world and they relate to climate factors. This determines how organisms pattern out  Large biological communities that we can divide organisms up into based on the physical environment, climate in particular  Biomes are organized by dominant plant types (not taxonomy) such as the Tundra or Boreal forest Why Plants?  Plants make up a large majority of the worlds biomass. They are visible, and cecile. Since plants cannot move, they are forced to deal with the temperature conditions year round. It is difficult to describe a region based on animals because they can migrate when weather conditions change.  Terrestrial biomes are characterized by succulence (leaves holding water) and deciduousness (leaves falling off) Major Plant Growth Forms  Deciduous: These trees are common in North America. They Plant growth forms lose their leaves in the fall.  Conifers: These are needle leave trees. They are found further North.  Cacti: These plants have adapted to a very dry environment. They have succulent stems and leaves.  Grasses: Grasses are different from other plants because they are not woody and they grow from their base (no stem). Because they do not grow from a stem, they are not typically damaged by Plant growth forms animals grazing.  Evergreen: These trees are found in the rainforest. They have broad leaves like trees in N.A but they do not lose their leaves as the temperature never gets cold (wet and warm year round).  Forbs: We have many of these in N.A. They are non woody, broad leaved plants like the Dandelion (seasonally cool environment).  Sclerophyllous: These plants have leathery leaves. They are found in environments that get very dry seasonally (seasonally dry/moist, warm/cool). Why Different Plant Growth Forms?  Selection Pressures  Selection pressures include: aridity, extreme temperatures, intense solar radiation, grazing and crowding  Similar growth forms can be found on different continents, even though the plants are not genetically related. This is through convergence. Convergence is when strong selective pressures happening in different parts of the world cause unrelated organisms to converge on a certain type of body plan. This is why we can have desert plants on opposite sides of the world. They are both part of the desert biome, but the desert plants in one area are completely different from the desert plants in another. They just converged on similar adaptations. Factors Affecting Plant Growth  Temperature has a direct physiological effect on Biomes Vary with Mean Annual Temperature and Precipitation plant growth  Precipitation and temperature act together to * but does not account influence water availability and water loss by for seasonal variation plants  Water availability and soil temperature also determine the supply of nutrients in the soil  Biomes vary with mean annual temperature and precipitation. This graph shows the 9 biomes. However, it doesn't take seasonal variation into account so the grasslands seem less prevalent than they are! Global Distribution  Human activities have changed biome distribution, land use change in particular (logging, Global Biome Distributions agriculture, resource extraction, urban development)  The actual distributions we see right now are very different. For instance, in London we are considered to be in the temperate forest biome. However, we do not see a lot of forested areas in Southern Ontario because it has been converted to agriculture.  Therefore, biomes are based on the dominant plant forms without human intervention.  In this map showing human impact, we can see that the warmer the colour, the more of an impact we have had on the biomes. The areas barely affected are cold, dry and unbearable. Global Biome DistributionsAre Affected by Human Activities Nine Major Terrestrial Biomes  Climate diagrams show the characteristic seasonal patterns of temperature and precipitation at a representative location Tropical Rainforests  Wet and hot (as shown in climate diagram)  More than 2X the amount of rain that we get in London Ontario. This means that these areas will be teeming with life (a lot of biodiversity)  The rainforest has not much more than 10% of the earth's surface but over 50% of species. We have high biomass and high diversity  Light in rainforest is difficult to get at because of tree cover so plants must grow tall to beat their neighbours out for light or adjust to low light levels (under trees)  Because it is so wet, plants have interesting strategies. Emergents are trees that grow above the canopy. Lianas (woody vines) and epiphytes grow on the stems or trunks of other plants (support). This is how they are able to get moisture!  In the rainforest, understory trees grow in the shade of the canopy and shrubs/forbs grow on the forest floor  The rainforest is productive enough to see different layers of plant growth :)  The rainforests are at threat due to logging, pasture and crop conversion. Only half of them are still intact  You would think that rainforests have nutrient filled soil because they are teeming with life but the nutrients are in the plants! The soils are ancient (were never glaciated so have been sucked dry of their nutrients). When you get rid of the trees, you lose nutrients and it takes a very long time to get them back! Recovery is questionable  This image shows deforestation over a 25 year period. You get a fishbone pattern which is caused by logging and road formation. There is very extensive rainforest removal in a relatively short period of time! Tropical Seasonal Forests/Savannahs  Warm, wet for part of the year, then get very dry  Associated with movement of ITCZ  Compared to the rainforest, we see shorter trees. They use the strategy of deciduousness in which they lose their leaves in the dry season. In these biomes we also see a lot more grasses and shrubs (sparse vegetation).  These areas typically look more like savannahs. Fire and large herbivores (wildebeests, zebras, antelopes, elephants) roaming the land may be the reason for this. Fires favor savannahs because they are more tolerant and grow back faster. A study in Africa found that elephants were running around and uprooting small trees which may have led to its conversion from forest to savannah. Flooding may have also had an effect (Orinoco River Floodplain)  Less than half of these biomes remain due to human population growth and agricultural impact. Hot Deserts  High temps, low moisture  Cannot support a lot of biomass (sparse vegetation/animal life and restrained plant growth due to low water availability)  Occur in areas of subsidence where you have high pressure systems. Even though it is warm, there is very little precipitation.  When deserts get a little bit of rain, plants/animals have adapted to take advantage. Plants can take in the water and grow flowers very quickly while the moisture is still available.  Many plants are succulent with stems that store water like cacti. There is such strong selective pressures in deserts that we see convergence (why you see 2 unrelated desert plants on opposite sides o
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