Question

. We have discussed how abiotic and biotic factors influence the composition and persistence of organisms in different communities over time.   Depending upon the organisms involved, the dynamics can vary dramatically.

a) One example of community change over time occurs during primary succession. Explain how abiotic and biotic factors influence community composition and changes, using examples of your choice. Address relevant environmental characteristics, ecological interactions, and life-history strategies in your answer.

2. The make-up of a community might instead change dramatically in response to a biological invasion. Using an example of your choice, explain how abiotic and biotic factors influence community composition and changes in response to the invasive species. Once again, address relevant environmental characteristics, ecological interactions, and life-history strategies in your answer.

Answer 1

a)         Both abiotic and biotic factors determine both where an organism can live and how much a population in a community can grow. A limiting factor is a factor that restricts the size of a population from reaching its full potential. The amount of food & water in a habitat is an example of a limiting factor. Other factors include geographical space, predation, climate, competition (for prey, food, mates) etc. An example of a limiting factor is sunlight in the rainforest, where growth is limited to all plants in the understory unless more light becomes available. Or perhaps in a deciduous forest, there are not enough rabbits to support the growth of more foxes. All species within an ecosystem will experience some kind of limiting factors to prevent continuous and exponential growth. (Even humans) Environmental changes (i.e drought, famine, human destruction) results in decreased rates of physiological processes, lowering the potential for survival, growth, or reproduction. Species will undergo Acclimatization to adjust to the new limiting factors through changing their behavior or physiology.

Limiting Factors:

· Light (exposure to light can change climate & growth of plants)

· Heat (will determine the weather/climate of an ecosystem)

· Mechanical Support (any features (i.e waterfalls, valleys, hills) which can either facilitate or inhibit a species survival

· Organic Matter (this will determine soil nutrition and therefore plant growth)

· Nutrients (Oxygen, Nitrogen, Carbon, Phosphorous etc.) are essential stability of an ecosystem

· Water/ Air (Water and Air quality will play a drastic role in the survivable of a species; streams, rainfall etc.)

· Predation (Predators will limit the growth of the population as well as human pouching)

· Competition (Competition within the species and with other species for food, water, mates will limit further growth)

· Geographical Space (If the species can only survive within a given ecosystem, the size of that ecosystem will prevent further population increases)

            Abiotic factors, such as temperature, soil and light, can also influence an organism’s success in an area. The tolerance range of an organism are the abiotic condition on which an organism can survive. At both the high and low ends of the tolerance range an organism is stressed. For example, lichens, have a low tolerance range when it comes to air quality, plants have a low tolerance range when it comes to temperature. Animals that can maintain relatively constant internal temperatures (endotherms) can live in a wide range of external temperatures, whereas ectotherms, which rely on the external environment are more restricted to the temperature they can survive in.

            Even with a mild spring, many outdoor plants we have in our gardens can be killed by frost. Large trees have a low tolerance to water that is why you don’t find them in deserts. Soil nutrient, acidity and salinity will determine the biodiversity and type of plants will can grow year round. For example the rainforest lacks sufficient nutrients for many high energy plants (i.e Deciduous Forests) to grow; whereas the desert suffers from high soil salinity and only succulent plants (i.e cacti) thrive.

a.

            Invasive species can have a number of negative impacts on the areas that they invade. Perhaps the most significant of these is the widespread loss of habitat. The hemlock woolly adelgid is an invasive insect from Asia that rapidly kills infested hemlock trees. In some parts of the Eastern United States, it is estimated that up to 80% of hemlock trees have been killed. These forests represent important habitat for many animals and with crucial habitat gone, species that rely on them may face extinction. Similarly, the health of many forests is threatened by kudzu vines, introduced from Japan in the 19th century as an ornamental plant. This plant was widely distributed across the Southeastern United States as a means of erosion control and as a food source for grazing animals. The vine soon became invasive, however, and can completely overgrow entire forests. In the process, it prevents sunlight from reaching the trees, effectively killing the forest. Additionally, the weight of the thick mats of vines on trees can cause trees to break and fall over. Its ability to quickly overgrow and destroy forests has earned it the nickname “the vine that ate the South.”

Some invaders can physically alter the habitat in addition to destruction. 50 beavers from Canada were relocated to Tierra del Fuego, an archipelago at the southern tip of South America, in 1946 to be hunted for their pelts. Since then, they have multiplied and now number in the hundreds of thousands. The trees in the region are not adapted to beaver activity as they are in North America, and most do not grow back after being gnawed by beavers. Portions of the formerly pristine forests now look like a bulldozer has plowed through them. Additionally, beaver activity creates ponds that flood portions of the forest. These bodies of stagnant water alter the nutrient cycle in forests and invasive plants thrive in them. Beavers also build dams in drainage ditches of grasslands and livestock commonly fall into them, where they become stuck and die.

Other invasive species may not destroy habitat but can have an impact by killing large numbers of endemic species. Burmese pythons, for example, are top predators in the Everglades. As such, they have decimated local mammal and bird populations. Capable of consuming deer and even alligators, these creatures eat virtually any animal they encounter in the Everglades. A number of threatened and endangered bird species have also been found in the digestive tracts of pythons, prompting concern that they could drive some species toward extinction. Lampreys in the Great Lake parasitize native fish. Because the native species have not evolved defenses to lampreys, they often die outright from wounds, or wounds become infected and eventually cause mortality. Invasive species can also threaten native species by outcompeting them for resources. Asian carp introduced into the United States, outcompete native fish for both food and space, leading to large declines in native fish populations. Invasive species are the second largest cause of species extinctions in the United States.

Invasive species can also impact human health. Invasive zebra mussels accumulate toxins in their tissues like PCB's and PAH's. When other organisms prey on these mussels, the toxins are passed up the food chain and can also enter animals consumed by humans. Ballast water from ships also sometimes contains harmful bacteria like cholera. Invasive animals can also be vectors for disease.

In addition to these impacts, invasive species can also have enormous economic costs. Zebra mussels in the Great Lakes can rapidly cover submerged surfaces, clogging up water intakes at water treatment facilities and power plants. Removing this invasive species costs an estimated $500 million annually in the Great Lakes alone. Power companies spend an estimated $1.5 million each year to control kudzu vines growing on power lines. Lampreys in the Great Lakes have decimated many fishery stocks to the point that they are no longer profitable. In the United States, invasive species cost an estimated $120 billion annually in control methods and in loss of environmental resources.

Factors affecting Invasive species:

• Host specificity and host availability
• Competitors
• Climatic requirements
• Latent period
• Sporulation potential and spore size
• Ability to survive in absence of hosts
• Epidemiology
• Phenotypic plasticity