Biophysical Field Methods

In this course, we want to dive into topics you might think you understand well: heat, temperature, water, and humidity. If you are an ecologist or biologist who measures or reports temperature or humidity, you need this course.

Temperature and heat. After viewing this lecture you should know the difference between temperature and heat and how they are related.

The three fundamental laws of thermodynamics made simple

Temperature scales, Fahrenheit, Celsius and thermodynamic (absolute). How temperature scale endpoints came about.

How to explicitly associate temperature to heat through knowledge of the specific heat of a material and thermal capacitance of an object.

Latent heat of vaporization and what happens when water changes from liquid to gas and vice versa.

The field course will involve gathering data and readying it for presentation as a poster. The capstone of the course will be a poster presentation to the Gobabeb community.

Creating an effective poster is an art. You want to convey your message, and you don't want to drive away people by forcing them to work too hard to understand your message.

Look at the three posters included as resources. These are from the 2019 offering of the field course. Imagine yourself looking at these posters in a crowded poster session. Ask yourselves these questions.

1. Which posters effectively communicate their messages?

2. Which posters do not?

3. How would you improve the posters to make them more effective?

4. What is the purpose of a poster, and how does it differ from a scientific paper?

Energy lifestyles --Here you will learn about ectothermic animals as energy misers and endothermic animals as energy wastrels andhow the body temperatures and energy budgets of the two groups differ because of their different lifestyles. The effects of body size on energy use are also discussed.

Definition of the operative temperature and how it relates to the first law of thermodynamics. Also, the mechanisms of heat transfer between animals and their physical environment and the energy balance equation.

In this section, modes of heat exchange are discussed and by its end you will have learned about heat exchange through radiation, convection and conduction.

The concept of the operative temperature is foundational to understanding the biophysics of adaptation. It is a thermodynamic temperature that is equivalent to the effective temperature felt by an animal or plant in a particular environment. It is the equilibrium energy balance, expressed as a temperature.

We will now go the next step and in this lesson you will learn to measure the operative temperature on "animals" of different sizes and colors. You will learn how the operative temperature is affected by radiation and convection and why small animals are coupled to convection, whereas large ones are radiation-coupled.

In this section we'll will teach you about the effects of body size, shape and color on the operative temperature. You will learn a simple way for estimating surface area of animals and then learn to write an energy balance equation, taking into account convection and solving for radiation. The result will be an equation for the operative temperature T_e.You will learn in some depth about the relationships and importance of volume and surface area and the terms radiation- and convection coupled.

In this section you will learn the effects of a shape closer to that of a real animal on its operative temperature. Obviously, the operative temperature of a sphere will be the same whichever side of it faces the sun. Not so for a flat leaf or a cylindrically shaped form. You will learn that a leaf's or a cylinder's operative temperature depends very much on which side of it faces the sun and that the area of the portion facing the sun can be viewed, and, if you like, measured as the object's silhouette.

This lesson will take you from models of animals studied und quite controlled conditions to learning how to measure operative temperatures under field conditions, where there are a wide variety of microclimates that an animal can occupy in a given habitat. You will also learn the utility of measuring the operative temperature of an animal (or plant). But before you can go out and measure these variables, you will learn how to calibrate your measuring devices. You will see three demonstrations of how microclimates can be used by animals and plants to their own ends.

In this video, we look more deeply into the boundary layer, and demonstrate the use of the hot-wire anemometer to measure the boundary layer more accurately. We then show how an understanding of the boundary layer can illuminate the building of large sand hummocks by a plant indigenous to the Namib: the !nara, Acanthosicyos horridus.

Here you will learn how to explain the daily pattern of behavior of an ectothermic animal by following its operative temperature.

Water has what are called colligative properties. These, the reduction of freezing point, the elevation of boiling point, the reduction of vapor pressure, and osmotic pressure, all depend on the concentration of solute molecules (or dissociated ions) in solution. In this section you will learn about these properties and their relationships with the environments in which animals and plants live.

This section will introduce you to water vapor in the air and its relations with water in the liquid phase. You will learn how to correctly describe water in these two phases and the basic physical principles of evaporation and condensation.

Here you will learn about the relationship between temperature and relative humidity and how relative humidity is a misleading measure. You will also learn about the use of a specialized iButton data logger called a Hygrochron to follow absolute and relative humidity over a 24 hour period.

This section deals with water potential in soils. You will learn how water actually moves through soils as a function of the interactions between the different forms of water potential.

In this part you will learn about the association between water potential and relative humidity and that water potential is the capacity to do work. Finally, you will learn about the water potential of air, what the measure of relative humidity is good for, and how water moves up in tall trees.

You will learn a simple method for measuring the water potential of the interior of a leaf, using a device known as a Scholander bomb, or a pressure bomb. The Scholander bomb uses an externally applied pressure to balance the water potential forces drawing water into a leaf.

In this section you will first review what you have learned about relative humidity then how to make molds of animals whose evaporative water loss you wish to study. That will lead you to the next section where you will learn to use the molds evaluate evaporation in several microhabitats.

Biophysical ecology often deals with periodic data, in which the values oscillate at some period, commonly 24 hours, or daily. Here, we learn some analytical techniques to help glean information from these data sets, and so to impart more meaning to the data. This video looks at a technique known as a phase plot, or a Lissajous plot

Another way to analyze periodic data is Fourier analysis. Here, we show how temperature distribution around leaves of Welwitschia mirabilis can be analyzed to clarify what the periodic drivers of leaf temperature are.

Here you will learn to measure water potential in the soil around a termite mound with a gypsum sensor and how to analyze these data using those from a previous project.

Based on the method learned in section 7.3., you will learn to analyze soil water potentials around a termite mound using data collected a few years ago when these mounds were being extensively studied. You will also learn what termite mounds are all about.

Nature is an unsteady place. A core concept like the operative temperature, in contrast, is a steady state condition. This, and the following lectures in this series, outline what the transient state is, its characteristics, and how to recognize it.

We measure the specific heat again, this time using methods to conserve heat, and provide a better estimate of the relationship between temperature and heat.

In the transient state, thermal capacity confers damping of fluctuating temperature driven by periodic forcing, as in the strong driver of daily insolation. We demonstrate this using the melon of the !nara, an indigenous cucurbit to the Amib desert. The melon is essentially a high thermal capacity package containing the seeds. What protection does damping of daily temperatures provide?

The time constant is a measure of the rate of equilibration. It is calculated from transient state data. It is the key to the quantitative analysis of the transient state

The time constant is a fundamental metric of the transient state. It is also the entry point for a number to tools for analyzing the transient state. Here we explore what the time constant can tell us about the interplay of resistance and capacitance for heat flow, underscoring what the proper role is for the operative temperature.

The time constant also lets one predict how a body temperature will follow a changing environmental (operative) temperature. This is possible through calculating two important quantities describing transient temperatures: the gain ratio and phase.

When animals move through habitats, they move through complex fields of operative temperature, owing to microclimatic variation of convection, radiation and conduction. How does an animal's thermal capacity respond? This video explores this issue and how to analyze it.

In the previous lessons, we explored the basics of the transient state for variation of body temperature driven by a variable operative temperature. We laid the theoretical groundwork on the question: What will happen to a beetle's body temperature as it traverses a ground that varies in temperature One item missing from that analysis was how fast beetles actually run? Here we outline a inexpensive method for measuring running speed from videos of beetles running.