The ecological apparency hypothesis and the importance of useful plants in rural communities from Northeastern Brazil: An assessment based on use value

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Abstract

The ecological apparency hypothesis in ethnobotanical studies predicts that the apparent plants (i.e., the most easily found in the vegetation) would be the most commonly collected and used by people. To test this hypothesis, it has been used the concept of use value (VU), which measures the relative importance of useful plants for a group of people. However, the use value has got some limitations, including the fact that it does not distinguish “current use” (plants which are effectively used) from “potential use” (well known plants, however not used). Therefore, this study has tested whether the obtained results through three different use value calculations could be useful in testing the ecological apparency hypothesis. These calculations have included the current use value, the potential use value, and the general use value. It has been carried out a vegetation survey and an interview for residents from the rural communities from Barrocas and Cachoeira (Soledade, Paraíba, Brazil). It has been used Spearman's coefficient to correlate phytosociological and ethnobotanical data. It has been observed that phytosociological parameters in Cachoeira were not correlated with any of the use values calculations, except the relationship between the current use value and the relative dominance (rs = 0.57; p < 0.05). In Barrocas, every use value calculation was correlated with the basal area and the relative dominance. When each category of use is analyzed separately, it has been observed that there was no correlation between the use value and the phytosociological parameters, except for the construction category, in which the current use value in Cachoeira was correlated with the relative dominance (rs = 0.63; p < 0.05), importance value (rs = 0.67; p < 0.01), relative frequency (rs = 0.71; p < 0.05), and relative density (rs = 0.72; p < 0.01). In Barrocas, the UVc for the construction category was correlated with relative frequency (rs = 0.69; p < 0.05) and relative density (rs = 0.66; p < 0.01). These results have suggested that, the use value calculation, which takes into consideration just the current use of the species, is the one that best fits in the ecological apparency hypothesis.

Highlights

► We used three different calculations of use-value to test the ecological apparency hypothesis. ► These calculations included the current use value, potential use value, and general use value. ► The current use-value calculation is the best suited to reveal relationship between the relative importance of a resouce and its apparency.

Introduction

In recent decade, ethnobotanical studies have analyzed the dynamics of people–plant relationships under different perspectives (Luoga et al., 2000; La Torre-Cuadros and Islebe, 2003; Shanley and Rosa, 2004; Hanazaki et al., 2006; Lucena et al., 2007, 2008; Reyes-García et al., 2007; Lucena et al., 2008; Ramos et al., 2008a, Ramos et al., 2008b). Thenceforth, several ecological hypotheses about the dynamics of foraging have stimulated the development of ethnobotanical studies, aiming to explain the use of plant resources in local communities. Among these hypotheses, it has been highlighted the ecological apparency hypothesis initially proposed by Feeny (1976) and Rhoades and Cates (1976), and first implemented in herbivory studies.

The ecological apparency hypothesis has proposed that there are two classes of plants: apparent and non-apparent, according to their availability to herbivores. Apparent plants are those easily visible due their size (trees, shrubs, and large herbs) or life cycle characteristics; non-apparent plants are small herbaceous plants of early successional stages (Albuquerque and Lucena, 2005).

Following the offer-demand principle, Phillips and Gentry, 1993a, Phillips and Gentry, 1993b have adapted this hypothesis for ethnobotanical studies, drawing a parallel between foraging animals and human populations. This way, apparent plants would be major targets for collection and use by humans (Albuquerque and Lucena, 2005; Lucena et al., 2008). To test this adapted hypothesis, Phillips and Gentry, 1993a, Phillips and Gentry, 1993b have developed a quantitative measure, the use value (VU) that attempts to measure the relative importance of given species to a human population based on their report about their use. According to the hypothesis, the most available species in woodlands would tend to have higher use value, being this relationship directly proportional, in other words, the higher the availability, the higher the use value of a plant.

After testing (La Torre-Cuadros and Islebe, 2003; Cunha and Albuquerque, 2006; Lucena et al., 2007; Ayantude et al., 2009), some limitations of the use value measure became apparent, mainly because the fact that it does not distinguish “the current use” (plants which are effectively used) from “potential use” (well known useful plants, however which are not used at all). This lack of distinction between current and potential use of a plant may influence in the conclusions about the vegetable resources use in human populations, considering the principles of the ecological apparency hypothesis. In other words, if the distinction is made between current and potential use of a species, the perceived relationship between the use and availability of a resource would likely change because people do not always use all resources they are aware of (Albuquerque, 2006; Estomba et al., 2006; Ramos et al., 2008a, 2008b). Some plants that are known by a human population may not be used currently, but may become incorporated or reincorporated into regular use in the future (Albuquerque, 2006).

In practice, it appears that the relationship between the availability of a plant resource and its actual use varies depending on the category of use. Lucena et al. (2007) have observed that the ecological apparency hypothesis correctly predicted the use of woody species. They found that use value was directly correlated with ecological dominance, whereas medicinal species (non-woody) had use values correlated only with relative frequency. However, these authors have calculated the use value without taking into consideration the effective uses singly. The same correlations were found by Lawrence et al. (2005).

Thus, in the context of these variations and limitations of the use value concept relative to the ecological apparency hypothesis, this study was carried out in the rural communities from Barrocas and Cachoeira (Soledade, Brazil), aiming to evaluate if different methods of calculating the VU of a species may interfere in the conclusions about its use and its relationship with this hypothesis, and change the list of the most important species locally, and the consequences of these variations for local conservation actions of such species. For a such end, it has been considered the following calculation ways of the VU: 1 - current use value (VUc), based only on reports of actual use of a plant; 2 - potential use value (VUp), calculated from reports of the known usefulness of a resource but not its actual use; and 3 - general use value (VUg), without distinction between VUc and VUp.

Section snippets

Regional context and study area

This study was carried out in Soledade city (Paraíba state, Northeastern Brazil). Soledade has got a warm, semi-arid climate (Köppen's BShs) with up to eleven dry months (Atlas Geográfico do Estado da Paraíba 1985) and a short rainy season with an annual rainfall of approximately 300 mm, one of the lowest totals in Northeastern Brazil (SEBRAE, 1998). The predominant vegetation is hyperxerophilous shrub-arboreal; important trees include Erythrina velutina Wildd. (mulungu) and Schinopsis

Vegetation survey

It has been recorded 29 species (28 useful) belonging to 22 genres and 14 families in Barrocas, and 19 species (16 useful) belonging to 16 genres and 11 families in Cachoeira. It has been surveyed woody species in the two communities that were not mentioned in the interviews, but they were excluded from data analysis.

Species richness in Barrocas was higher because woodlands were on private properties so that only permitted people could exploit plant resources there. Another factor that may have

Relative importance versus availability

Based on the comparisons between the use values and phytosociological data, it has been observed that all three use values have been strongly correlated with basal area and dominance in Barrocas. In Cachoeira, there was a strong correlation between VUc and dominance. This positive correlation between these parameters may reflect a more intense exploitation of woody plants, primarily for construction purposes (fencing, for example) and fuel (firewood) in both communities. A similar relationship

Conclusion

Results from this study indicate that the method of calculating use values presented here provides more useful information, confirming the limitations in the VU calculation available in the literature, which does not differentiate between use and knowledge.

Based on the findings of this study, it has been suggested that additional studies may be carried out in other humid and dry tropical forests to confirm whether the modifications for use value calculation affect lists of the most locally

Acknowledgements

We would like to thank the residents of Cachoeira and Barrocas for their help during this study and CNPq for providing the research grant to R. F. P. Lucena and the research productivity grant to U.P. Albuquerque and E. L. Araujo. We are also grateful to the Almeidas (Marisete, Germano, Geane, Geano and Gilbervan) for all their help and friendship, to Josê Pereira Soares for his assistance during fieldwork, and to the members of the Laboratory of Applied Ethnobotany at the Rural Federal

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