| Summary: | 碩士 === 中國文化大學 === 景觀學系 === 102 === Human activities and habitat change have caused dramatic changes to global biodiversity. Biological introductions and invasions aggravated by human activities is one of the most important factors affecting biodiversity globally, and is widely researched and discussed. Taiwan's geographical environment and climate nurtures a rich diversity of birds. However, with the international trade and convenient transportation system in recent years, the introduction of exotic species has caused serious environmental problems. Of the exotic birds in Taiwan, starlings, especially white-vented myna (Acridotheres javanicus) and common myna (Acridotheres tristis) were found to be the most abundant and widely distributed. The native crested myna (Acridotheres cristatellus) of Taiwan has been negatively affected by exotic mynas. The purpose of this thesis was to study the long term trends of the native myna and the two exotic mynas in Taiwan, and through analyzing the relationship between trend variation of the three mynas and land use change data, understand if there were similarities and differences in their habitat requirements, and how land use change affected their communities.
We used the avian survey data (from 1986 to 2010) of 102 study sites in Taiwan from the bird record database managed by the Chinese Wild Bird Federation (CWBF). We used two types of compilations of the bird data: The first data set was the presence/absence of the three mynas in each survey, and the second data set was the frequency of occurrence (%) at each study site. Landscape was analyzed at two scales: a 1km*1km ecological and environmental GIS database, and a 1/5000 land use survey data. The land use survey data included two periods, once during 1992-1995, and once during 2006-2008. To match the land survey data, the bird data was also selected for two five-year periods 1991-1995 and 2006-2010 during habitat analysis. First we used principal component analysis to help downsize the data set, and finally chose 25 variables. Chi-square test, T-test, ANOVA analysis, Classification regression tree, Logit generalized linear model, Generalized linear model and Linear regression models were used to test 11 proposed hypotheses of myna habitat preferences. Trends across the twenty five years showed that the frequency in which the native crested myna was observed decreased while the other two exotic mynas (white-vented myna and common myna) increased. White-vented myna, in particular, increased faster than the common myna. The results of hypothesis testing found: 1) The three mynas all preferred urban environment. 2) The three mynas all preferred lowlands. White-vented myna and common myna were distributed primarily below elevation 250M; native crested myna was distributed primarily below elevation 125M. These two results confirmed that the three mynas preferred urban environments in lowlands. 3) The three mynas preferred green space, but showed less preference for wetlands, barren land, and agricultural lands. 4) The three mynas also showed preferences for specific types of green spaces. Crested mynas showed a stronger preference for more natural green spaces; white-vented myna showed slight preference for natural green spaces; and the common myna showed preference for artificial green spaces. 5) The best habitat models for the three mynas changed during the two periods in ways that suggested that habitat selection may be affected by population size: the myna with the largest population were more strongly associated with their favorite microhabitats; the mynas with smaller populations relaxed their habitat choices to include less favorable microhabitats within preferred macrohabitats. 6) Changes in myna frequency were analyzed using changes in land use to form transition models to see if changes in myna populations were affected by land use changes. Results suggested that riparian land converted to other uses such as parks will increase the frequency of exotic species (common myna), and the reduction in natural grassland will decrease the frequency of native crested myna. 7) Further analysis of landscape composition suggested that landscapes with more than 2% natural grasslands were found to have higher crested myna frequency.
Habitat models, transition models and hypotheses testing results all suggested that relatively natural grasslands was the most important microhabitat affecting native crested myna. Green space planning should allocate at least 2% of the overall landscape to relatively natural grassland to improve native myna habitats. Also, locations currently with higher native crested myna populations should be maintained with higher natural grass cover, and measures taken to reduce the exotic mynas populations in these locations to assure dominance of the native mynas in these areas. Areas of importance identified by this thesis includes: Guandu Nature Reserve (Taipei), Hua jiang bridge (Taipei), Puli Kung Tin ditch (Nantou), Shezi (Taipei), Shimen Laomei (Taipei), Huazhong Bridge (Taipei), Danda mountain(Taipei), Tianliaoyang(Taipei), Budai (Chiayi), Jinshan(Taipei). Through such measures, native crested myna populations may have a higher chance of survival.
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