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To what extent does plasticity of dipterocarp seedlings affect growth and survival in the tropical rainforest environment?

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Introduction

To what extent does plasticity of dipterocarp seedlings affect growth and survival in the tropical rainforest environment? 050139246 The Journal of Ecology (September 2007) To what extent does plasticity of dipterocarp seedlings affect growth and survival in the tropical rainforest environment? Abstract This study focused on survival and growth of three dipterocarp seedlings in exposed areas compared with shaded areas of the tropical rainforest, in order to determine the role plasticity plays in this. All species of dipterocarp seedlings showed some degree of morphological plasticity in response to the different environments. Each of the three dipterocarp species showed equal plasticity in terms morphological traits when subjected to different light conditions. Chlorophyll content was found to be a genetic trait rather than a trait of plasticity. Herbivory was also found to be determined by species rather than environment. Damage by herbivores was found to play a larger role in plant growth and survival than anticipated, perhaps more so than plasticity. Further study is required to determine the extent herbivory affects the growth and survival of these seedlings. Introduction The importance of tropical rainforests and their role in supporting much of the world's biodiversity is widely acknowledged, yet there is worldwide concern over the consequences of human activities on these ecosystems. (Myers et al, 2000) The lowland forests of Sabah, Borneo are dominated by trees of Dipterocarpacae; a family which is both ecologically and economically important. ...read more.

Middle

There were highly significant differences between the heights of the three dipterocarp seedlings in response to the different light environments (ANOVA: F=17, df=1,11, p<0.005) with seedlings being taller in the gaps than the shade. However, there were no significant interspecific differences (ANOVA: F=0.4, df=2,11, p=0.68)(Figure 2). There were no significant effects of gap and shade environments on the shape of the three dipterocarp seedlings (ANOVA: F=0.1, df=1,25, p=0.955), nor were there any significant interspecific differences (ANOVA: F=1.63, df=2,25, p=0.215) (Figure 3). There was a highly significant effect of gap and shade environments on the SLA for each dipterocarp species (ANOVA: F=31.3, df=1,11, p<0.001) with seedlings having a greater SLA in the shade then the gaps. However there were no significant interspecific differences (ANOVA: F=2.74, df=2,11, p=0.108)(Figure 4). There was no significant difference in chlorophyll content of the three dipterocarp seedlings in response to the different light environments (ANOVA: F=0.35, df=1,11, p=0.565). However, there was a significant difference between the species (ANOVA: F=8.98, df=1,11, p=0.005) with S.macroptera having a significantly greater chlorophyll content then D.lanceolata, (Tukey multiple comparison test p<0.05). H.sangal was not significantly different from either of the other two species (Tukey multiple comparison test p>0.05)(Figure 5). There were no significant effects of gap and non gap environment on the average herbivory percentage damage of the dipterocarp seedlings (ANOVA: F=2.3, df=1,11, p=0.158). However there were highly significant interspecific differences (ANOVA: F= 21, df=2,11, p<0.001), with S.macroptera having a significantly greater average herbivory percentage damage than the other two species (Tukey multiple comparison test p<0.05)(Figure 6). ...read more.

Conclusion

Furthermore, some of the S.macroptera had not survived in the shaded plots, which additionally reduced the sample size. However, averaging the data will have reduced any bias caused by the limited sample size. Secondly there were diverse variances of the three dipterocarp species for each of the traits. For example those seedlings in the gaps had particularly large variances. This is explained by gap heterogeneity. Different gaps have differing light intensities and even across the same gap the light can vary (Brown 1983). Nevertheless, the two-way ANOVA analysis method was appropriate since it is robust enough to deal with the unequal variances between the treatments. Another criticism is that since this study was conducted in the field it was difficult to control all conditions that have affected the results. Further research using an artificially controlled environment would be useful to compare results and widen understanding of this area. In conclusion, all species of dipterocarp seedlings showed some degree of morphological plasticity in response to the different light environments. Each of the three dipterocarp species showed equal plasticity in terms morphological traits when subjected to different light conditions. Chlorophyll content was found to be a genetic trait rather than a trait of plasticity. Herbivory was also found to be determined by species rather than environment. Damage by herbivores was found to play a larger role in plant growth and survival than anticipated, perhaps more so than plasticity. It has a negative effect on plant fitness by repressing growth and reducing competitive ability. Further study is required to determine the extent herbivory affects the growth and survival of these seedlings. ...read more.

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