Origin and Distribution of Communities

29.1 Ecological Succession A series of changes in which different species appear, only to be replaced later by others. Biotic and Abiotic factors change over time. Some communities are more stable than others.

Succession and its Causes Succession can occur where no life previously existed or where an established community exists. Succession is caused by the effect a particular set of organisms has on the environment. These changes make life more or less suitable to other organisms.

Succession and its Causes Examples: Soil erosion and runoff into a pond Volcanic eruption Clearing of land by humans Changes in climate and precipitation. In any succession, the resulting plant life will determine what new species will inhabit the area.

Succession and its Causes Different stages of succession will be defined by different sets of dominant plant species. Mosses and grasses tend to appear first. Trees appear and become dominant much later.

Primary Succession This is succession that begins in an area where there is no life. Begins with very hardy organisms – pioneers – that can grow under adverse conditions – pioneer stage. Example: New England Forest Lichens produce acid that breaks down rock into soil. As lichens die, bacteria breaks them down, adding nutrients. Mosses may grow, then grasses, shrubs, larger plants, then finally trees.

Primary Succession

While the changes are occurring in the plant species, there is an impact on the animal species as well. The more plant life appears, the more microenvironments will develop. Example, shady area of the forest vs. sunny area in clearing. The appearance of forest doesn’t end succession. Pine trees give way to deciduous trees. Climax community – the final, stable (be careful here) stage of a community.

Climax Community Are more stable for the most part, but changes in climate, disease, natural disaster, or human interference can change community temporarily or permanently. Human intervention may be so severe succession may start over again, though not from the pioneer stage.

From Pond to Forest Ponds can be relatively stable, but are not climax communities. Life span depends on its size and conditions of the environment. Consider pond surrounded by forest:

Secondary Succession Occurs more rapidly than primary succession, mainly because soil is already in place. Succession does not always lead to the same climax community. Old abandoned farm places are an example.

Trends in Succession As it occurs, small plants with shorter life cycles are replaced with larger plants with longer life cycles. With more producers, the amount of energy trapped by photosynthesis increases. Diversity increases as it continues. Food chains start simple and become more complex. More complex food webs means less energy wasted. Recycling of materials also becomes more efficient.

29.2 Biomes Different biomes determined by environmental factors: Temperature Humidity Precipitation Factors determined by: altitude, latitude, wind patterns, and topography (surface characteristics).

World’s Biome Distribution

Biomes Precip cm/year Tundra – 12 cm Taiga – cm Temperate Forest – 100 cm Tropical Rain Forest - >200 cm Grassland – cm Desert - <10 cm

Ocean Surface of the Earth more than 2/3 water. The kind and number of organisms living in the oceans far exceeds those on land. Abiotic Factors: Light – intensity decreases with depth (generally does not get further than 200 meters) Producers live only where there is accessible light.

Abiotic Factors continued Temperature – it is important, but it does not vary as much as it does on land. Why? Example: Mid-Atlantic Ocean, temperatures vary only about 10 degrees Celsius from the top to the bottom.

Organisms Ecologists classify aquatic organisms into 3 main groups: Plankton – organisms that float in the water and are carried by currents algae, protists, small multicellular animals Nekton – animals that move freely through the water under their own power fish, whales, shrimp, squid Benthos – Organisms that live attached to or crawl on the bottom. barnacles, starfish, sponges, clams – most found at shoreline or close to it in shallow waters

Zones Neritic Zone – area above the continental shelf Oceanic Zone – region of deeper waters of the ocean basin Littoral Zone – portion of the neritic zone closest to shore – most likely to change Influenced by tides, temperature changes, runoff, salinity changes

Zones

Circulation of Water In cold climates, surface water becomes colder. Cold water is more dense than warm, so it sinks. Warmer water below rises. Also, wind pushes surface water in a direction, and water from below fills in. Important because nutrient from decomposed matter are returned to the surface to promote plant growth.

Circulation of Water

Unique Ocean Communities Deep-sea vents – areas where the bottom water is warmed by vents from the magma below. Animals like 3 foot long tube worms, clams, octopus, unusual fish live here

The Biosphere Important to point out that all land and sea biomes interact with each other, just as micro communities interact within an ecosystem. What happens in one region may impact another. Great example is El Nino effects.