Exercise+2_Climate+and+Microhabitat

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Apr 3, 2024

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Exercise 2: Climate and Microhabitat ( Adapted and edited from Brewer & McCann 1982; Brower, Zar, & von Ende 1998) This Killdeer was observed on a ‘nest’ it made in the parking area between the Science II building and Barstow Ave. Why would it choose this odd ‘microhabitat’ for such an important life-history activity? Introduction As we discussed in lecture and as is covered in SimUText, climate, season, and weather affect the distribution and activity of both terrestrial and aquatic organisms. Climate refers to the general prevailing atmospheric conditions over the years in a given region. Climates are usually characterized by seasonal temperature, humidity, and precipitation. Weather refers to the momentary conditions of the atmosphere. Four major physical factors compose the atmospheric component of a habitat such as air moisture, temperature, wind, and solar radiation. Extremes, rather than averages, of these variables usually affect the distribution and abundance of organisms. In this lab exercise, we will focus on variation in simple climatic factors across small scales of space and time (microclimate). Climatic variables largely determine the type of biotic community in an area and the distribution of individual species. We will pay similar attention to the analysis of weather conditions that largely affect the daily and seasonal behavior and abundance of species. Background: Climate Climates are often broadly categorized by latitude as polar (or arctic), cold temperature (or boreal), temperate, and tropical, with terms such as subtropical or subarctic

denoting intermediate climates. Temperature and precipitation are characteristic variables. Recall that biomes distinguish both climate and predominant vegetation in large geographical areas. For a more detailed picture of the climate for a given region, ecologists use two types of climate diagrams (aka climatographs). In Figure 2B.1, the mean monthly temperature and the mean monthly precipitation are plotted for each month of the year, and the plotted points are connected sequentially to form an irregular polygon. Data for this type of graph are available from local weather stations or from government documents prepared by the National Oceanic and Atmospheric Administration (NOAA), Washington, DC (http://www.ncdc.noaa.gov); and regional climate centers (http://met.www.cit.cornell.edu/other_rcc.html). A second method of presenting the climate of a given region is to graph the mean monthly precipitation and mean monthly evapotranspiration as functions of time of year. Figure 2B.2 is an alternative presentation that helps to diagram water availability based on readily obtained temperature and precipitation data. As evapotranspiration is directly related to temperature, a plot of seasonal changes in temperature will be similar to a plot of evapotranspiration. A temperature of 10 ° C is considered roughly equivalent to 20 mm of monthly precipitation in terms of evapotranspiration (Walter, 1985). Consequently, points on Figure 2B.2 where temperature and precipitation curves intersect represent a condition where the amount of water lost through evapotranspiration is about equal to the amount gained through precipitation. Thus, in Figure 2B.2, July and August would have a water deficit in the Pacific Northwest but would experience a water surplus for the mid-Atlantic coast of the United States. Microclimate Variation in the local climate due to such factors as elevation, slope, vegetation, and shade can result in temperatures, humidities, and light intensities quite different from those of surrounding areas. For example, the atmospheric conditions in a forest on a north-facing slope are quite different from those on a south-facing slope ( Is this statement true in both the North

and South hemisphers?) . Microclimate can also vary due to the influence of and variation in the heat-absorbing properties of ground cover such as rock, soil, vegetation, or water. We will focus on horizontal profiles of these variables where zonation or patchiness occurs within the habitat. Our microhabitat study will include analysis of light , humidity , wind speed , and temperature in specific locations, including: 1) an open gravel area, 2) in a mini ‘greenhouse’, 3) in a stand of trees, 4) the edge of a pond, 5) over a pond . For this lab exercise we will meet in our usual lab location (S 322) but conduct our measurements in the areas just south of the greenhouse near the planetarium. Specific Measurements 1. Atmospheric Conditions Record the atmospheric conditions at the time of sampling (e.g. sunny, cloudy, etc). 2. Light Intensity The intensity and duration of solar radiation affects other atmospheric variables (such as temperature, relative humidity, and wind) and the amount of energy available for primary production, and the timing of seasonal cycles of plants and animals. Luminous intensity (measured in a variety of units including watts/area, candlepower, or lux). For example, the amount of light received 1 m from a standard candle is a lux; that received at a distance of 1 ft is a footcandle . Use the meter to measure light intensity in lux at each location. Your instructor will show you how to work the instruments. 3. Humidity Atmospheric humidity is the amount of water vapor in the air. It has important biological effects on plant respiration, on rates of transpiration and evaporation, and on the amount of cooling surfaces from which evaporation takes place. The amount of water vapor in air may be expressed as vapor pressure , the partial pressure of water vapor in the air. It can be stated as millibars (mb) or as an equivalent height of a mercury column, as in a barometer: 1 mm Hg = 1.333 mb; 1 mb = 0.7501 mm Hg (Metric) 1 in. Hg = 33.86 mb; 1 mb = 0.02953 in. Hg (English units) The maximum amount of water vapor that the air can hold when in equilibrium over liquid water is called saturation vapor pressure and is directly related to temperature. The vapor pressure deficit is the difference between the saturation vapor pressure and the actual vapor pressure. The most common measure of atmospheric water vapor content is relative humidity , the actual vapor pressure expressed as a percentage of the saturation vapor pressure. It is

important to note that rates of evaporation are not directly related to relative humidity, but are a function of the vapor pressure deficit and the air temperature. 4. Wind Speed Wind speed can affect the distribution of heat and the removal of moisture from a habitat, affecting the relative humidity of the surrounding air. 5. Temperature a) Air temperature : Measure air temperature approximately 0.5m above aground (~ knee high). Take care to shield the temperature measurement device from direct sunlight. You can use either the onboard temperature measurement or the thermocouple probes to measure air temperature. b) Surface temperature : Touch the tip of the thermocouple probe to the ground surface, or place just below the water surface of the pond. Again, take care to shield the measurement device from direct sunlight. c) Instantaneous temperature : Temperature measured at a specific point in time. d) Diel (24hr temperature) temperature : Temperature measured across the 24-h day cycle. Would we expect the same amount of temperature variation across microhabitats over a day, regardless of their instantaneous temperatures at a specific time? Part of this lab will be to propose a simple measurement experiment using very small temperature probes to take temperature readings in various microhabitats every 15 minutes over a 24 hr period. Propose a study that will examine what variables affect the stability (or variation) of temperature over a given 24-hour period. Sources: Brewer, R., and M.T. McCann. 1982. Laboratory and field manual of ecology. Saunders College Publishing, Philadelphia. Brower, J.E., J.H. Zar, and C.N. von Ende. 1998. Field and laboratory methods for general ecology, 4 th Ed. WCB/McGraw-Hill, Boston. __________________________________________________________________________

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