Tropical And Seasonal The Climate Of The Malagasy West Coast

Organisms of the ecosystems of the dry forests along the Malagasy west coast show distinct adaptations to the marked seasonality of this region. All plants and animals occurring here need to cope with the long and relatively cold dry season during the austral winter, with virtually no precipitation and no open water available from April through October (Figure 1). The dry season alternates with the rainy season, which lasts from mid-November to mid-March, with most rain

Joanna Fietz • Department of Experimental Ecology, University of Ulm, Ulm, Germany K.H. Dausmann • Department of Ecology and Conservation, Biocenter Grindel, University Hamburg, Hamburg, Germany

1999 2000 2001

Figure 1. Climate of the Kirindy forest. Shown are data from March 1999 to August 2001, taken at a standard location in the field camp. Temperature is given as monthly mean ± standard deviation. For precipitation cumulative data per month are shown. (•) Daily maximum temperature; (o) daily minimum temperature. Data on daily minimum temperature are not available for April 2001. Note the interannual variation in climate, especially in the timing and amount of precipitation.

1999 2000 2001

Figure 1. Climate of the Kirindy forest. Shown are data from March 1999 to August 2001, taken at a standard location in the field camp. Temperature is given as monthly mean ± standard deviation. For precipitation cumulative data per month are shown. (•) Daily maximum temperature; (o) daily minimum temperature. Data on daily minimum temperature are not available for April 2001. Note the interannual variation in climate, especially in the timing and amount of precipitation.

falling during the hottest months between December and February. Mean annual precipitation is 800 mm (range 390 - 1511 mm; Ganzhorn and Sorg, 1996).

While average daily maximum temperature is comparable between dry and rainy season (around 32°C; Table 1), average daily minimum temperature differs dramatically between the two seasons, with ambient temperature dropping to about 13°C at night during the dry season, but only to about 23°C during the rainy season. The average amplitude of daily temperature fluctuations is therefore about twice as great during the dry season (about 19°C) than during the rainy season (about 10°C; Table 1). The coldest months are June and July, with ambient temperature dropping below 10°C at night (Figure 1).

Concomitant with these climatic changes, variations in the availability of food resources like fruits and insects occur. Even though fruits are produced throughout the year, the percentage of fleshy fruits decreases dramatically during the dry season (Bollen et al., 2005). Insect abundance is positively correlated with rainfall and leafing of the trees, and therefore insects are also less abundant during the dry season (Hladik et al., 1980).

The austral winter in the dry deciduous forest of western Madagascar thus represents a bottleneck of energy and water supply, combined with energetically disadvantageous low ambient temperature. However, the occurrence of this period of scarcity is very predictable, giving organisms inhabiting these ecosystems the opportunity to take measures to master these challenges.

Table 1. Climate of the Kirindy forest
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