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3. 3 – Studying Organisms in Ecosystems Organisms are not distributed evenly across Earth

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3.3 – Studying Organisms in Ecosystems
Organisms are not distributed evenly across Earth.

  • Climate is determined by temperature and precipitation, which, in turn, results from the unequal heating of Earth, and other factors, such as proximity to large bodies of water and local geography.

  • The unequal heating of Earth’s surface causes Earth’s major climate zones from the tropics near the equator, through the temperate zones, to the cold regions near the North and South Poles.

  • The pattern of precipitation influences the soil that forms in these different regions. Soil conditions, moisture levels, altitude, latitude and temperature determine the types and abundance of plants.

  • The plants determine the variety and population sizes of organisms that inhabit an area.

A biome is a large geographical region with a specific climate, and the plants and animals that are adapted to that climate.

  • Contain a dominant species such as prairie grasses in a grassland biome.

  • Biomes consist of many different habitats, each defined by the particular local biotic and abiotic factors.

  • A habitat is a place, or physical setting, in which an organism lives. Each species is found in the specific habitat that it’s physical, physiological, and behavioral adaptations equip it to survive and reproduce in.

  • The range of a species is the geographical area where the species is found.

The hoary marmot (Marmota caligata) Range of the hoary marmot

feeds on plants found in high altitude


Canada has 4 major Biomes as well as contact with fresh water & marine biomes.

Terrestrial Ecosystems – ecosystems found anywhere on Earth not covered by water.
Alberta: 2 major Biomes

  1. Taiga

  2. Grassland

Ecosystems of the Taiga Biome (Boreal Forest)

  • Found along the Rocky Mountains and throughout northern Alberta.

  • Dominated by conifers (needle trees)

    • Adapted to warm, moist summers and cold dry winters.

    • Thin needles = less water loss

    • Wax coats the needles further preventing water loss and protects against frost damage

    • Pyramid shape, small needles and flexible branches help shed heavy snowfall.

  • Different regions of the taiga forest can have different ecosystems.

    • The forest canopy is the upper layer of vegetation. It receives lots of sunlight. Mature conifer trees, such as spruces and pines, reach this area. Conifers are suitable as food for about 50 species of birds.

    • The forest floor receives very little light. Vegetation found here is shade loving such as shrubs, mosses, and ferns. Primary consumers include moose, voles, and white tailed deer. Predators include bears, weasels, owls, and wolverines.

Muskeg Ecosystems

  • Within the taiga biome, there is a range of climate conditions, and thus, a range of ecosystems.

  • In areas with warmer ground temperatures, there is rapid decomposition of organic matter = good soil.

  • The decomposition of needles produces acidic soil in which only certain plants can grow.

  • The northern regions are cold enough that a layer of permafrost is found beneath the soil that never melts.

  • Rain and melted snow cannot drain away, and the water soaks the decomposing plants and peat moss.

  • This forms muskeg, ground that is swampy or boggy in the summer.

  • Decomposition of plant and animal material is slow.

  • Plants adapted to this ecosystem grow close to the ground and have fibrous roots that anchor them into the shifting soil. Plants include lichen, mosses, tall grasses, small shrub.

Ecosystems of the Grassland Biome

  • Central and southern Alberta

  • Very fertile soil.

  • Short-lived grasses with deep roots provide a large biomass for decomposition.

  • Warm temperatures cause rapid decay and the formation of a rich layer of humus (decaying plant and animal matter).

  • Grass length is controlled by precipitation.

  • Grassland ecosystems have only one layer in which to support the biotic community, limiting the number and diversity of organisms.

  • Producers include rough fescue, wheat grass, and spear grass. Deer, squirrels, and rabbits graze on the grass.

Deciduous Forest Ecosystems

  • Found at the edges of the grassland biome, before it turns into taiga (central Alberta)

  • Increased sunlight and warmer temperatures compared to muskeg and taiga biomes

  • Deciduous trees and shrubs found here.

  • Warms temps, more precipitation, and large amounts of humus from the leaves create rich soils.

  • In the spring, most of the sunlight reaches the forest floor and the understory (below the canopy layer; shrubs and smaller trees).

  • In the summer, only 6% of the sunlight reaches the ground.

  • Supports a great diversity of animals.

    • Thick layer of leaf litter supports many insects.

    • Insects support a variety of insect eating birds and mammals.

    • Rich vegetation and understory support large browsers such as deer and moose.

Aquatic Ecosystems

  • Water covers 2/3 of our planet

  • Ponds, rivers, lakes, and oceans

  • 97% saltwater

  • Oceans provide a constant supply of freshwater through evaporation

  • In Alberta, the major aquatic ecosystems are freshwater

  • Zones in a lake have different physical properties, such as differing temperatures and amounts of light. This results in a variety of habitats within an ecosystem

  • Littoral zone – the area from the shore of a lake or pond to the point where no ore plants grow in the lake bottom

    • Bulrushes and water lilies

  • Limnetic zone – the area of a lake or pond in which there is open water and sufficient light for photosynthesis to occur.

    • The word plankton is used to describe both the autotrophic (tiny plants and algae) and heterotrophic (invertebrate animals) microorganism found in this zone.

    • Plankton are the food for consumers at the higher trophic levels, such as fish, tadpoles, and birds

  • Profundal zone – the region of a lake beneath the limnetic zone, in which there is insufficient light for photosynthesis to occur.

    • Not found in ponds

    • The source of nutrients in this zone is the rain of dead plants and animals that falls from the limnetic zone.

    • Detritus is slowly broken down by bacteria or consumed by other bottom-dwelling invertebrates and fish, called detritus feeders.

    • Bacteria use O2 to decompose detritus = ↓O2 for other organisms which means only those that can live with ↓O2 can be found in this area.

    • Benthic zone = bottom of the lake.

Ecological Niche

  • Ecological niche – an organism role in the ecosystem.

  • Its place in the food web, its habitat, its breeding area, and the time of day it’s most active, etc.

  • The variety of niches and habitats within an ecosystem allow it to support a diversity of organisms.

    • For example, even though the red-tailed hawk and the great grey owl eat some of the same food, they are not in competition because they have a different ecological niche.

Factors Limiting Growth in Ecosystems

  • A limiting factor is any biotic or abiotic element that controls the number of individuals in a population.

  • Abiotic factors include: soil, water, sunlight, air, or minerals

Limiting factors prevent these bacteria from reproducing infinitely.

    • Interspecific competition – competition between two or more populations for limited resources, such as nutrients, light, or living space.

    • Intraspecific competition – competition for limited resources among members of the same species.

Sea Anemones compete for the territory in tide pools


    • Predation – interaction that involves the consumption of one organism by another.

    • Parasitism – one organism (the parasite) derives its nourishment from another organism (the host).
Density-dependent factor: a biotic factor that limits a habitat’s carrying capacity (max pop. size that an environment can sustain), the impact increases with the density of the population (e.g., parasites, disease)
Density-independent factor: an abiotic factor that limits a habitat’s carrying capacity (e.g. fire, flood); the impact is not affected by the density of the population
Biotic potential – highest growth rate for a population given unlimited resources and ideal living conditions.

    • Under these conditions population growth is exponential and we expect to see a J curve on a graph.

    • Only exists in theory, in practice there are always limiting factors. So true population growth creates an S curve as populations encounter environmental resistance (limiting factors.)

Sampling Populations in Ecosystems

  • Organisms can be sampled using transects or quadrats situated randomly in a sample area. From these samples, the density of a population can be estimated.

A 5m × 100m transect

A quadrat is a square (of either metal, wood, or plastic) used in ecology to isolate a sample, usually about 1m2 or 0.25m2. The quadrat is suitable for sampling plants, slow-moving animals (such as millipedes and insects), and some aquatic organisms.

Assignment: p. 108 #’s 1-5

Review p. 110

1→4, 6, 7, 8, 9, 11, 13, 14, 15, 16, 18

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