Review Ecosystems Key Information Types of Symbiosis Species

Review Ecosystems Key Information

Types of Symbiosis Species A Species B Mutualism + + Commensalism + 0 Parasitism + -

Roles in Ecosystem ROLES Producer Consumer Decomposer

Competition • Populations compete for limited resources such as water, energy, living space, and mates. Competition within a species may result in the better-adapted individual (better able to get food, water, territory, mates, etc. ) eliminating the less fit competitor. • Interspecific (between species) competition negatively effects both competing populations. Both populations will be reduced in number due to competition for limiting resources.

Competition

Succession • Minor changes occur as one species slowly replaces another in response to such factors as climate changes, human impact, or introduction of foreign species. • In land environments, succession is driven by the plants. • There are two main types of succession, primary and secondary.

Primary Succession • Primary succession occurs when no soil is present. Therefore, the organisms that migrate into the area must contribute to soil formation before other, larger plants can move in. Weathering begins breaking down the bare rock into smaller particles, and then pioneer species can move in. Lichens are a good example of a pioneer species. Lichens attach themselves to rocks with root-like rhizoids. They secrete acids onto the rock surface, dissolving the rocks. This begins the formation of soil.

Primary Succession

Secondary Succession • Secondary succession that takes place when soil is already present, usually following a catastrophic event that partially or completely removes the existing vegetation. Secondary succession occurs much faster than primary succession because soil already exists, a healthy seed bank in the soil may be present, or rootstocks of previous plants may still be viable. Secondary succession usually begins with fast growing herbaceous ground cover that stabilizes the soil.

Interactions of Biotic and Abiotic Factors within an Ecosystem

SOIL – Has both biotic and abiotic components

Changes in Ecosystems • Humans have impacted practically every ecosystem on Earth. • Humans have over-fished the oceans, polluted water sources, caused deforestation, eradicated entire species, or introduced new invasive species. Most human activities cause changes to the ecosystem in one way or another. • Natural forces are also factors that cause ecosystems to change. They can be large scale natural changes such as fire or they can be slow changes such as erosion.

Biodiversity • Biodiversity describes the variation of organisms found in an ecosystem. • Biodiversity is the foundation to a healthy ecosystem and may be impacted by pressures that cause environmental change such as habitat loss, the introduction of invasive species, climate change, fire and resource management. • The development of roads, pipelines, and power lines causes natural habitats to become fragmented into islands and negatively impacts the natural flora and fauna of the area.

Invasive species • Invasive species are also a threat to biodiversity and impose enormous costs to agriculture, forestry and fisheries. • The introduction of the alien species may be accidental or intentional. • The introduction of non-native animals, plants or microbes can result in serious problems. • For example, if the non-native species does not have natural predators in their new environment, then they may potentially rapidly reproduce, out-compete the native species in the area and alter natural habitats. The spread of invasive species is a serious problem and may cause extensive damage to ecosystems.

Climate Change • Climate change is another factor that impacts ecosystems. • The effects of climate change are already evident in some ecosystems. • According to the EPA, “As the climate continues to warm, major changes may occur in ecosystem structure and function, species’ ecological interactions, and species’ geographic ranges, with predominantly negative consequences for biodiversity. In addition, climate changes such as increased floods and droughts are predicted to increase the risk of extinction for some plant and animal species, many of which are already at-risk due to other non-climate related factors. ”

FIRE • Fire is another important natural occurrence that causes drastic changes to ecosystems. • While many mistakenly believe that fire only causes danger, this is far from the truth. • Fire helps maintain such ecosystems as grasslands from turning into forests or scrublands. • Fire also helps to promote new growth in forest by clearing debris from the forest floor and allowing the germination of seeds. In fact, some trees like the redwoods and giant sequoias need their seeds “heat treated” by fire to germinate.

Humans • There are trade-offs associated with resource management and protecting the environment. Overall, the impact that humans have on the environment is negative. • However, humans have taken action to improve the ecosystems that were damaged or destroyed by human activities. Examples of humans changing the environment to make a positive impact are natural/wildlife preserves and national parks. These areas of land that are protected, managed, and conserved for the benefit of the environment. Many cities participate in recycling programs, which limit the amount of trash that enters the landfills and decreases the demand for non-renewable resources. New fuels and improved engines reduce pollutants into the atmosphere.

Ecology • Ecology is the study of interactions between living organisms in a given area and their surroundings. • Organisms are impacted by their environment and in turn, impact their environment. • The living part of this world is referred to as the biotic community.

Biomes of the World • Biomes are recognized as the broadest area of interactions in ecology. • These areas such as deserts, rainforests or grasslands are defined by two major climatic factors: precipitation and temperature.

Biomes • Other local factors such as topography, wind patterns and ocean currents will have modifying effects on regions. • In addition to particular climate factors, each biome is defined by its major vegetation type, which influences the types of animals and other organisms living in that biome. • Biomes can be subdivided into smaller units called ecosystems.

Growth of Populations • An organism’s maximum ability to increase its population size is referred to as its biotic potential. • This occurs under optimal conditions such as no limits to food, water, living space, diseases and predation. • This type of growth pattern is called exponential growth and is illustrated with a J-shaped curve.

Growth of Populations

Environmental Resistance • While populations may experience this type of growth, it is often only for brief periods. • Seldom do all of these optimal conditions exist at any one time. • More often, an organism’s growth meets environmental resistance, which results in decreases in birth rates or increases in death rates. • These decreases or increases are related to environmental conditions such as availability of food or predation. • In this case, the growth of the population is represented by an Sshaped curve.

S-shaped curve showing a population has reached its carrying capacity.

Abiotic and Biotic Factors Affecting Population Growth • The carrying capacity is the size of the population or community that can be supported by the surrounding environment. • In determining the carrying capacity of any environment, biologists identify limiting factors to population growth. • These either promote or hinder growth and can be divided into abiotic or biotic factors.

Abiotic Factors Affecting Population Growth • Temperature • Precipitation • Soil p. H • Soil nutrients • Space availability • Length of growing season • Light availability • Water availability

Wind Effect on Tree Growth

Biotic Factors Affecting Population Growth • Disease • Competition • Predation • Behaviors of living organisms

Once a population reaches its carrying capacity, the size of a population might fluctuate due to interplay of the limiting factors within the environment.

An environmental carrying capacity is subject to change • Environments may degrade resulting in the shrinking of the carrying capacity. • In this case, the environment is no longer able to support a population of organisms that formerly have lived in an ecosystem on a sustainable basis. • No population can live beyond the environment's carrying capacity for very long. • Over grazing by herbivores or the introduction of a new disease or predator may reduce the carrying capacity. This may lead to a drop in the number of organisms in the ecosystem. After this drop in the population, a new carrying capacity may be established.

Change in the carrying capacity over time

Both abiotic and biotic factors can be limiting • Since ecology focuses on the interaction of organisms with their environment and to other living organisms, these factors (abiotic and biotic) cannot be viewed in isolation. • Both types are also referred to as limiting factors, since they determine the types and number of organisms in the environment. • For example, plant growth is restricted in the tundra due to the short, cool summers, coupled with harsh winters and permafrost in the soil. Trees cannot survive under these conditions. However, the plants that are present grow low to the ground and tend to be annuals.

The actions of living organisms will have similar effects - Predation • In certain environments, keystone predators are important in restricting the population sizes of some organisms and preventing the disappearance of other populations. • This can be seen in the kelp forests along the Pacific coastline in California. Young kelps are grazed by sea urchins. If left unchecked, the sea urchins can overgraze the kelp beds leading to their reduction in size. This normally does not happen because in this situation, the sea otter acts as a keystone predator and preys upon the sea urchins keeping their populations in check. This allows a kelp forest to maintain itself and provide a habitat for many other organisms.

Predation can also lead to fluctuations in population size of both predator and prey • The Canadian lynx and snowshoe hare is a classic example of how populations of predators and prey can fluctuate. The population peaks for these two organisms is offset. The rise in the lynx population occurs only after the hare population has begun to rise. Then as the lynx population increases, predation upon the hare reduces its population. • Other limiting factor like climate or disease could also affect the numbers of both organisms.

Canadian lynx and snowshoe hare

Plants and animals in each biome have developed specific adaptations for survival • To survive the harmful effects of fire, grasses have their growing regions located below the surface of the soil. Therefore, the growing regions are protected from the fires that periodically burn across the grasslands. • In another example, deciduous trees drop their leaves in the fall to avoid damage to during the cold winters. Also, cold winters reduce or stop the ability of deciduous tree to carryout photosynthesis. In a sense, these trees “hibernate” to overcome their ability to function normally during winter conditions. • In addition, some organisms may migrate or hibernate to avoid harsh winter conditions.

Adaptive Strategies of Desert Plants Succulence Drought Tolerance Drought Avoidance Absorb large amounts Grow annually, grow Shed leaves during dry of water in a short and die quickly. Shed periods period of time seeds for next season Have extensive system horizontal, shallow roots Larger, deeper roots Have a thick waxy cuticle Develop mechanism to absorb moisture from dry soils Stomata open at night rather than the day Germinate when soil moisture conditions are optimal Not all seeds germinate, even under optimal conditions