3.2 Study Guide Flashcards
Define species richness and species evenness. Explain how two communities with the same richness can have different evenness.
Species richness refers to the total number of species in a community while species evenness refers to how the individuals of a community are proportionately spread between species. Two communities have the same richness but different evenness when they have the same number of species but different percentages of the total population of individuals making up each species (individuals are spread between species differently).
What does the Shannon-Wiener Index measure in a community? What kind of community would have a Shannon-Wiener Index value of 0?
The Shannon-Wiener Index measures the uncertainty of one randomly chosen individual in a community being a given species in that community. It is defined by both the richness and evenness of a community. A community with an index value of 0 would have only 1 species present - the minimum richness and maximum evenness.
An African savanna community is made up of 5 Buffalo, 8 Impalas, 7 Zebras, and 12 Dik-Diks. Determine the richness of the community, then determine the Pi value for each species. Using the Pi values and the richness, calculate the community’s Shannon-Wiener Index Value and then its evenness.
The community has a richness of 4, having 4 total species. The species Pi values are 0.15625 (5/32), 0.25 (8/32), 0.21875 (7/32), and 0.375 (12/32) for the Buffalo, Impalas, Zebras, and Dik-Diks respectively. Using these values to calculate, the community’s evenness is equal to (-((ln(0.15625) x (0.15625)) + (ln(0.25) x (0.25)) + (ln(0.21875) x (0.21875)) + (ln(0.375) x (0.375))). After calculating this equation, the community’s Shannon-Wiener Value equals out to ~1.3369. Now that the community’s richness and Shannon-Wiener Value are known, its evenness can be found using the equation E=~1.3369 / ln(4). After calculating this equation, the community’s evenness equals out to ~0.9644.
Define ecological succession. What are two of the three main differences between primary succession and secondary succession?
Ecological succession is the process by which an environment and the species within it naturally changes and grows over time.
Differences between primary and secondary:
1. Primary begins with barren land while secondary begins with a climax community.
2. Primary does not begin with any soil while secondary begins with soil present.
3. Primary typically takes around 100-200 years to reach a climax community while secondary typically takes only 50-100.
What kinds of organisms typically make up pioneer species? What is the role of pioneer species in primary succession.
Pioneer species generally consist of various kinds of bacteria, lichens, mosses, and sometimes ferns or other very low-lying plants. These species’ role is to grow over barren land and create a starting layer of soil with their decomposed biomass, which can then support larger plant life.
What happens to pioneer species and following seral-stage species once larger and larger plant species begin to grow throughout an ecosystem? Why is this?
As pioneer and seral-stage species make an ecosystem more fertile and habitable during ecological succession, the newer plants that the environment begins to be able to support are generally larger and taller than their predecessors. This size and height difference gives the newer species advantages for absorbing sunlight, moisture, and nutrients from the soil compared to “older”, smaller plants. The new plants’ advantages allow them to grow and propagate quickly, but they also inhibit the growth of older species and reduce their populations harshly.
What is a keystone species? What is an invasive species? How can the introduction of invasive species potentially wipe out an entire ecosystem?
A keystone species is a species whose existence and niche are integral to the existence of its entire ecosystem due to being the base of a chain of species relying on each other for food and/or survival. An invasive species is one that benefits its natural environment but is introduced into a different environment where it is not limited by another species and causes uncontrollable damage (it is only considered invasive in its non-native environment). The introduction of an invasive species into an ecosystem can be dangerous to both species that is preys upon and other species that prey upon those species. If a species put at risk by an invasive species is a keystone species, than it could potentially spell disaster for the entire ecosystem.
Define a climax community. What are three factors that can affect what types of plants grow in a climax community?
A climax community is the final stage of ecological succession. It is marked by the introduction and growth of larger, slow-growing plants and relatively high fertility supporting a wide variety of both plant and animal species.
Factors that can affect plants in climax communities: Sunlight, Humidity, Temperature, Water, Soil Nutrients, etc.
Give an example of a natural event that can spark primary succession, an example of a natural event that can spark secondary succession, and an example of a form of human activity that can spark secondary succession.
Natural events causing primary succession: Volcanic Eruptions; Glacier Movement; etc.
Natural events causing secondary succession:
Sustained Floods; Wildfires; Disease; etc.
Human activity causing secondary succession:
Logging/Deforestation; Pollution; Global Warming and Climate Change causing Extreme Weather; etc.
Define both genetic diversity and ecological diversity. How can one affect the other?
Genetic diversity is the variance in genetic combinations within a given population of organisms. Ecological diversity is the number and variance of different habitats found within a given ecosystem. Generally, more and more varied habitats support more and more niches that can be filled by different organisms, supporting genetic variance and adaptation. On the other end, low genetic variance typically causes evolutionary bottlenecks in which populations cannot very well adapt to their environments and grow, which can lead to unfilled niches and the collapse of habitats.
Two communities of birds live in different nearby ecosystems. Community 1 has 16 species with an evenness of ~0.76 and a Shannon-Wiener Index Value of ~2.11. Community 2 has 19 species with an evenness of ~0.71 and a Shannon-Wiener Index Value of ~2.09. Which community is more biodiverse and why?
While Community 2 does have higher richness than Community 1, which is usually a sign of higher biodiversity, its lower evenness and especially its lower Shannon-Wiener Value show that it isn’t quite as biodiverse as Community 1 despite having very similar values.
