Relationships between stream habitat and breeding territory length of the Brown Dipper (Cinclus pallasii) in Taiwan |
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Authors: | Chao-Chieh Chen and Ying Wang |
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Institution: | (1) Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung, 80742, Taiwan;(2) Department of Life Science, National Taiwan Normal University, 88 Ting-Chow Rd, Sec 4, Taipei, 11650, Taiwan |
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Abstract: | Dippers from the genus Cinclus are highly specialised predators on aquatic invertebrates, and occupy linear territories along rivers where measurements
of variations in quality are relatively straightforward. For these reasons, they are ideal model species in which to examine
factors affecting territory size. In this paper, we investigated the influence of stream habitats on the territory length
of the Brown Dipper (Cinclus pallasii) in Taiwan. The biomass of aquatic insects and other stream habitat variables were analyzed to determine their relationships
with the territory length of Brown Dippers from November 1988 to May 1989. Compared with slow-moving waters, riffle areas
contained significantly greater insect biomass (paired t test, t
11 = 3.49, P < 0.01), of which trichopteran larvae contributed about 70%. Dippers spent more time foraging in riffles than in slow-moving
waters. In addition, dippers preferred foraging in shallow riffles, but avoided deep, slow-moving waters (G = 62.53, df = 3, P < 0.001). Territory length (1,045 ± 165 m SE], n = 14) was negatively related to proportion of riffles (r
2 = 0.5715, P < 0.01), total aquatic insect biomass (r
2 = 0.5840, P < 0.01), and altitude (r
2 = 0.7176, P < 0.001). In factor analysis, four factors were extracted from the 14 stream variables. However, only factor 1 was significantly
related to territory length (r
2 = 0.5207, P < 0.01). Factor 1 explained 42.8% of the total variance and collectively revealed the importance of high food abundance.
In other words, Brown Dipper territories were the shortest along high-altitude streams with abundant riffles, fewer pools
and abundant aquatic insects. These results indicate that abundant supply of accessible invertebrate prey is the most important
factor affecting the territory length of Brown Dippers. This is consistent with Cinclus species elsewhere, and reveals the importance of clean, productive river ecosystems. |
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