BIO 103

Biology 103

Ecology Activity Worksheet for

Some Animals Are More Equal than Others:

Trophic Cascades and Keystone Species

Video Link for Activity

PROCEDURE: After watching the video, use the information to answer the following questions in the space provided.

*Then upload the completed work to the appropriate assignment box by the assignment due date.

1. Are all members of a food web equal in abundance and in their relative effects on one another? Why or why not?

2. Explain the reasoning or evidence you used to answer Question 1.

3. Is every member of a food web the prey of another member of the food web?

4. Explain the reasoning and include evidence you used to answer Question 3.

5. When Robert Paine removed the starfish from an outcrop in Mukkaw Bay, what did he find happened to the number of different species that were also present on the rocky outcrop over time? (Did they increase or decrease?)

a. What species population increased significantly in number on the rocky outcrop, and why?

6. Before the 1960s, most ecologists thought that the number of producers in an ecosystem was the only variable that limits the number of herbivores. The idea was that every level was regulated by the amount of food from the trophic level below it.

a. How did the green world hypothesis differ from this “bottom-up” view?

b. Imagine a simple food chain: Grass -> Grasshoppers -> Mice. If snakes that eat mice are added to the ecosystem, how would you redraw the food chain to represent this change? Using names and arrows is acceptable.

c. After the snakes are added, would you expect the amount of grass to increase or decrease? Explain your reasoning.

7. Since 1972, Dr. Jim Estes had been studying a food chain of kelp -> urchins -> sea otters. In the early 1990s, sea otter numbers started decreasing due to a new apex predator eating the sea otters. What was the new apex predator and what circumstances caused it to depend on sea otters as a food source?

BIO 103 Chapter 2

Overview

Chapter 2 introduces ecology will which then be applicable to the various animal groups covered later in the semester. Ecology is the scientific study of organisms and their interactions with the biotic (living) and abiotic (nonliving) factors in their environments. There are levels of ecological organization. The most narrow ecological level is physiological ecology (also includes behavioral ecology). Note that behaviors may be learned or innate. The following ecological levels become progressively more broad: population ecology, community ecology, ecosystem ecology,…(levels exist that are not addressed in the textbook), and concluding with the study of the biosphere (the larges complex of ecosystems on earth).

Many biotic and abiotic factors affect organisms. Predation, competition, and symbioses are examples of biotic factors. Symbioses include parasitism, commensalism, and mutualism. Abiotic factors, such as temperature, in the environment also impact organisms. Environmental resources include both biotic and abiotic factors such as plants as “food” sources and space availability, respectively. A niche is composed of all aspects of how a species makes its “living”. The dimensions of the niche can vary among individuals within the species ,and the species’ niche may change over generations. Also, distinctions are made between the fundamental and realized niches of species.

Population ecologists examine a variety of factors that affect populations (or demes) and metapopulations. Demographics can incorporate age structures, sex ratios, and growth rates. The demographic characters of different species can vary dramatically. Survivorship curves model survival and mortality among individuals in a population. Age structures can suggest if a population is likely to increase or decrease over time. Populations have intrinsic growth rates and population growth can be exponential or logistical. Logistical growth includes environmental limitations on population growth potentially resulting in population size reaching (or hovering/ oscillating around) carrying capacity (K). Density-dependent and density-independent factors can affect populations and population growth.

Community ecology involves examining more than one population in a particular area. There are many examples of coevolution with respect to species’ evolution in communities. Symbiotic relationships are a component of community ecology. Note that parasites can be endoparasites or ectoparasites. Predation and competition between species, as well as herbivory are community level ecological factors. Predators and prey evolve “new” adaptations as do herbivores and the plants they consume. Competitive selective forces often drive evolution to reduce niche overlap between species. The Galápagos finches exemplify ecological character displacement, in addition to adaptive radiation. Communities often have keystone species, a species whose influence on other species is so dramatic that its presence affects the dynamics of the entire community. Keystone species are often predators, but they do not have to be.

Ecosystem ecology examines communities and the abiotic factors that affect those communities. For example, trophic structures examine the flow of energy through a food web. Primary producers, such as plants and algae, are the photoautotrophic organisms in the ecosystem. The primary consumers are herbivores (or omnivores) that feed upon the producers. Secondary, tertiary, etc… consumers are the omnivores and carnivores that feed upon the consecutive consumers in the level below. Decomposers are important consumers because they help to recycle nutrients back into the ecosystem. Due to the Laws of Thermodynamics, especially the Second Law of Thermodynamics, ecosystems have a limit to the number of trophic levels. Unlike nutrients, energy is not recycled through the ecosystem. (Note the major nutrient or biogeochemical cycles of carbon, nitrogen, and phosphorous.) Ecological pyramids depict the food web with respect to biomass. Unlike biomass pyramids, energy pyramids are never inverted due to energy lost as heat during each energy transfer of the trophic structure.

Ecological biodiversity is often defined as an ecological measure of species richness (number of species) and the relative abundance of each species. Biodiversity results from the average rates of extinction being lower than the average rates of speciation over time. Scientists suggest that about 99% of all species that have existed are currently extinct. (Remember, scientists recognize at least five major mass extinctions throughout earth’s history.) Biodiversity and conservation are major ecological topics today. Many factors impact biodiversity, and there are conservation efforts to address some biodiversity questions, for many species including animals. Of what examples or approaches for animal conservation are you aware?

Reference: Hickman, C.P. Jr., et al., Animal Diversity

Chapter 2

Animal Ecology

Talkeetna Mountain Range, Alaska
©Cleveland P. Hickman, Jr.