| Introduction to Biogeography | |||||
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| Climate and range | |||||
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| Premise: Climatic factors act as primary controls on the distribution of many organisms. You are provided with data on significant climatic characteristics at stations within the geographic range of Thuja plicata (western red cedar) and T. occidentalis (eastern cedar). Use these data to compare and contrast the climatic environments presently occupied by the two species. We will assume throughout this exercise that Thuja plicata consists of two independent populations: one restricted to the coast, the other in the continental interior. We can divide the main climatic controls on species distributions into two broad categories; temperature and moisture. Because temperature regimes commonly control the length of the growing season for temperate and arctic plant species, the critical aspects of the temperature regime are therefore: a) the relative length of the seasons of growth ("summer") and dormancy ("winter"); b) the relative warmth of summer; c) the relative severity of winter TASKS Length of the growth and dormancy seasons 1. If we assume that at least some plant growth can be sustained on any day when the maximum temperature exceeds 0°C, how long is the potential growing season in the areas inhabited by Thuja plicata (coastal and interior populations should be treated separately) and T. occidentalis? Use the data in Tables 1 and 2a and 2b to plot the relative lengths of the growing seasons on the graph paper provided. [2] 2. If the plants are frost-sensitive during their growth period, how might this restrict the length of the potential growing season? Plot the length of the frost-free period in areas occupied by T. plicata (coastal and interior) and T. occidentalis. [2] 3. What do you conclude about the distribution of the species populations with respect to growing season length? [4] Thermal characteristics of the growing season 4. Plot the range of mid-summer temperatures (mean July and extreme maximum temperatures) over the species ranges. [2] 5. Plot the accumulated warmth of the growing season (degree-days: base temperature 5°C). [2] 6. What do you conclude about the distribution of the species populations with respect to growing season warmth?. [4] Thermal characteristics of the dormant season 7. Plot the range of mid-winter temperatures (mean January and extreme minimum temperatures) over the species ranges. [2] 8. Gardeners commonly use minimum temperature data to determine whether a plant species that they wish to plant will survive in their local area. They generally rely on data represented in maps of plant hardiness zones. What is the zonal range of Thuja in North America? [3] T. plicata (coastal): zone___ to zone ___ (warmest to coldest) T. plicata (interior): zone____ to zone ___ (warmest to coldest) T. occidentalis: zone_____ to zone _____ (warmest to coldest) 9. What do you conclude about the distribution of the species populations with respect to dormant season conditions? [4] Moisture Availability Insufficient moisture may restrict the range of drought-sensitive plant species. How do the North American Thujas compare in terms of the moisture availability in their range? 10. Plot the distribution of the threeThuja populations in terms of the mean annual precipitation in their range. [2] 11. Plot their distributions in terms of the annual moisture index. [2] 12. What do you conclude about the distribution of the species populations with respect to moisture availability? [4] 13. Do the coastal and interior populations of Thuja plicata occupy areas of distinctly different climates, and are their climate regimes different from that of T. occidentalis? Summarize the main differences in point form. [3] |
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