Research Paper on Trends and Dynamics of Bird Species Extinctions in Amazon Rainforest Fragments 1979-2001

Introduction

By reading the title and the abstract of the article, it is seen that the article seeks to investigate trends and dynamics due to landscape for bird species extinctions in the Amazonian rain forest fragments between the years 1979 to 2001. Further, it enquires whether these incidents of extinctions were documented during the period of isolation and after it. In itself, the abstract section provided adequate information to properly summarize what the paper is all about since it clearly states what the study objectives are. The research confirms that the extinctions occurred during the stated periods with about 37 bird species going extinct. Additionally, it affirms the fact that factors like fragment sizes and landscape effects have great effects on bird populations in the neotropical sites during the period.

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Analysis of the Introduction

From the introduction section, the article explains the required understanding of the types and numbers of bird species that can be supported on a given fragment area as this is useful for conservational planning purposes. Isolation predicts that the fragment area constrains the species population in a given area and the degree of isolation exhibited by the species. Matrix dynamics play a crucial role in determining the structure of such communities of birds. Alternatively, the developed second-growth framework provides for increasing domination of new fragments by other species. However, different species exhibit different kinds of responses.

Most studies in the past have adopted frameworks that cannot determine the changes in the species population due to non-periodic surveys. An exceptionally long history of bird species extinction has been reported from the Neotropical site of Panama (BCI) where there have been reports of the interior species getting lost through the 1960s (Naka, Strong, and Philip 89). The areas of La Selva in Costa Rica and other areas of the lowland peninsula have also been experiencing a reduction in the number of some bird species (Naka et al. 89). The article further brings up Brazil-based Biological Dynamics of Forest Fragments Project (BDFFP) that applied the mist netting program to collect data on birds' loss of species from the fragments for about 12 years beginning from the year 1979. The four methods applied by Ferraz et al. (2003) focused on the estimation of the time taken to lose half of the originally present species (t50) in a given fragment have also been elaborated on. The methods include minimum, Bayesian decay, runs test, and jackknife. While the first three methods modeled the species disappearance from a fragment only once without factoring in the effects of recolonization. The last method used the calculations of the species population based on the previous years' numbers, and this factored in the effect of recolonization of fragments by the various bird species.

The article's key objectives aimed at answering some pertinent research questions related to the bird species extinction in the rain forest fragments. To begin with, the question 'Can variation in extinctions among fragments be explained by variation in the matrix structure or other landscape effects?', Seeks to address the aim of the experiment of examining fragment size and landscape effects on the extinction of bird species. Secondly, the question 'Which species detected in 1991-92 were not detected in 2000-01?' Seeks to address the extinctions that had been reported in the rain forest isolated fragments between 1992 and 2001. Works from the authors like Ferraz et al. (2003), Robison (1999), Ewers & Didham (2006), and Renjifo (2001) among others greatly support the ideas presented in the introduction section of the article. In the reference section, the article Avian Community Dynamics in a Fragmented Tropical Landscape. Ecological Applications by Borgella, R & Gavin, T.A. (2005) provides more closely related information to the topic. The article explains the fragmentation of bird species in the tropical landscapes with their application to ecological planning, just in line with the topic of discussion (Naka et al. 90).

Analysis of the Results

Figure 2 is most helpful because from it, the extinction rate of the bird species between the years 1992 and 2001 just at a glance. It provides mean, maximum, and minimum portions of the bird species that were captured in 1992 but not in 2001 for n=4 1-ha fragment, n=4 10-ha, and n=2 100-ha fragments. For the table, Table 1 is most helpful since, from it, the species that went extinct can easily be spotted. It gives the comparison tally of each bird species in given fragment sizes between the years 1992 and 2001 (Naka et al. 91). Additional information that can be got from the text portion is that there was an increase in species or fragments in 2001 as compared to 1992, but all the fragments considered lost close to 37 species.

Analysis of the Methodology

The methodology for the research involved the use of the mist net from the lines of 8 or 16 nets samples put up within the fragments and netted between 0600 and 1400 h for a day at a time, for 2000-01 sampling was done six for eight times while for 1991-92, it was done for eight times with a 1 to the 2-month interval between each sample. At this point, the explanation of the method applied is clear and short and, therefore, can warrant a repeat by another researcher. Further, four models were used to explain variables like distance to forest, border age, and matrix age as linear predictors, each considered for a given fragment at a time. Afterward, the obtained data from the application of each sample was applied to calculate the maximum-likelihood sum of squares and Akaike Information Criterion for small samples (AICc) such as weights and evidence ratios (Naka et al. 91). Before the application of the statistical methods, the researchers applied capture data collected in the earlier years of 1979-1990 by regular sampling. This enabled maximum projection of the bird species to be targeted in the sampling procedure by mist net sampling.

Analysis of the Discussion

The model that best described the data was jackknife estimates. It produced the best matching data since it did not assume the yearly decay in the number of species like the other three model; hence, the effect of recolonization was appropriately captured. Based on the fragment size effects, there was an inverse proportionality between the species lost and the fragment size, ranging from 6 percent in the n=2 100-ha fragment to 47 percent in the 1-ha fragments (Naka et al. 91). Modest space requirements of the species and lack of competition are likely to make a specie less sensitive to the effect of fragment size whereas low sensitivity of a species makes it more sensitive to such effects.

Conclusion

In summary, this research helps to develop some important patterns in the bird species population in the tropical rain forest areas. It shows the predictability of the extinctions, stabilization of the fragment richness as long as recolonization is permitted, and the extinctions that occur among the bird species of such areas as a result of isolation events. As long as the surrounding forest habitats of the species under study become hostile, their richness diminishes as a result of increased epidemics.

Work Cited

Naka, Luciano. Strong, Cheryl and Philip, Stouffe. Twenty Years of Understorey Bird Extinctions from Amazonian Rain Forest Fragments: Consistent Trends and Landscape-Mediated Dynamics. 2009.