General Ecology: Lecture 1



General Ecology: Lecture 1

Introduction; Abiotic Factors (begin)

I. My background and interests in ecology

II. Course Policies and Schedule

A. Course overview and policies handout

B. Role of lecture and textbook in learning the material.

C. Writing intensive aspects of course

D. Math background: Math 111 or equivalent is highly recommended.

E. Brief review of schedule

III. What is Ecology?

A. Definition (one of many):

1. “Ecology works at characterizing the patterns seen in nature, studying the complex interactions among organisms and their environments, and understanding the mechanisms involved in biological diversity.”

B. Clarify each part of that definition (stream ecology examples…):

1. Characterizing the patterns seen in nature. This is descriptive work requiring careful observation.

a) Example 1: Spatial patterns (i.e. The River Continuum)

← Many differences are seen between the upstream and downstream stretches of a river (examples…)

b) Example 2: Temporal patterns (i.e. Life Histories)

← Aquatic insect example

2. Studying the complex interactions among organisms and their environments. This goes beyond basic descriptions, and attempts to understand cause-effect relationships currently in operation. Detailed observations, experimentation and models.

a) Example: What causes the differences seen between upstream

b) How does introduction of non-native trout to a stream impact stream macroinvertebrates?

3. Understanding the mechanisms involved in biodiversity. This not only deals with the current interactions, but also an understanding of underlying evolutionary mechanisms.

a) Why do some reaches of a river tend to have greater diversity than others? Why do some rivers have greater diversity than others?

b) Why do tropical rain forests and coral reefs have relatively high species diversities compared to other ecosystems?

4. NOTE: While we will not conduct experiments that allow us to verify cause-effect relationships or mechanisms of biodiversity in the stream ecology study, you will have the chance to read about these types of relationships and speculate upon them in the Introduction and Discussion sections of your papers.

C. Ecology is an interdisciplinary science with conceptual and methodological contributions from many fields.

IV. Importance of abiotic factors to the distribution of species

A. Overview:

1. The absolute geographical boundaries of a species are set by abiotic factors.

a) Global scale

b) Local scale

2. Within those limits set by abiotic factors, biological interactions further shape the presence/absence/abundance of species.

a) NOTE OF CAUTION: A species may not exist in a region where it could physically tolerate conditions because it simply hasn’t immigrated there yet.

← Polar bear example

B. Shelford’s law of tolerance (pp. 81-83): It is the limits of an organism’s physiology that determine where its potential physical boundaries are [Fig. 5.1]

1. Look carefully at axes and their meaning.

a) x-axis: “environmental conditions” usually is meant to represent the continuum of a particular abiotic factor

← Examples…

b) y-axis: “response of species” is generally synonymous with an individual’s fitness in the absence of competitors, predators, etc...

← How would you measure this?

2. Examine the different regions within the range of tolerance.

a) Know these different regions!

3. Different life stages may have different tolerances.

a) Blue crab example

4. Seasonal shifts in tolerances [Fig. 5.2]

a) Acclimatization: Rapid, relatively short-term shift in tolerance range in response to changing environmental conditions

← Example: Increase in RBCs with increased altitude.

5. This is a simplified view. You have a graph like this for each important physical characteristic.

a) However, there may be one clearly important physical characteristic that determines range. Example: winter distribution of the eastern Phoebe (from Krebs, Fig. 7.6)

C. Role of natural selection in shaping these boundaries: These boundaries are not fixed over time; natural selection can create shifts in tolerances of species to particular environments.

1. For what time scales (relative to a species’ life history) would this matter?

D. Global climate change and its impacts on species distribution

1. Example: Mosquito species carrying the malarial parasite Plasmodium spp. are shifting both to higher altitudes on mountains and to higher latitudes due to increases in global temperatures.

Study questions:

1. For the definition of Ecology given in today’s lecture, provide some examples of questions related to each “key phrase” of the definition.

2. In general, which type of factors set the absolute geographic boundaries of a species? Provide examples.

3. You discover an area that appears to be suitable for a particular species based on its abiotic requirements. However, you do not find that species present anywhere within its boundaries. Provide two distinct, alternate explanations for its absence.

4. The x-axis of the Shelford’s Tolerance graph is labeled with some type of “Environmental Condition.” (Know this!) Provide some specific examples of abiotic conditions that could be important in determining a species’ geographic range.

5. The y-axis of the Shelford’s Tolerance graph is labeled as “Response of Species”. Provide at least one appropriate way you could measure this,

6. Put it all together: Explain Shelford’s Law of tolerance with words and diagrams (including properly labeled axes). Be sure you explain the difference between the differently shaded areas of the diagram.

7. What is meant by “seasonal or geographic shifts” in tolerance? Be sure you understand the diagram used to explain this concept. (Fig. 5.2 in text.)

8. If you were drawing a Shelford’s Law diagram for the Eastern phoebe, what would -4ºC correspond to on the diagram?

9. Explain why mosquitoes have expanded their range both north and south of the equator in the past decade, and also occur at higher latitudes than in previous decades. Include a Shelford’s tolerance graph with appropriately labeled axes as part of your explanation.

10. Define “acclimatization.” Define “natural selection.” What effects do acclimatization and natural selection have on tolerance limits? Compare the time-scale of acclimatization to that of natural selection.

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