Distribution and population status assessment of the endemic grass-like palm Butia marmorii (Arecales: Arecaceae) in Paraguay

 

 

 

Introduction

 

Conservation status assessment is extremely useful in conservation biology as a planning tool for conservation actions, focusing the budget (always low) on specific targets that try to improve conservation outputs (Caro & O’Doherty 1999; Simberloff 1998). The most widely utilized assessment of conservation status is the method proposed by the International Union for Conservation of Nature (IUCN), and its website is one of the most popular references for citing the conservation status of different taxa; however, only 5% of the world’s described species have been globally evaluated (IUCN 2016). The IUCN Red List of Threatened Species 2016 database shows 483 palm species assessed (IUCN 2016). This number represents only 19% of the total palm species recognized (2522 species) (Dransfield et al. 2008). Of the 483 palms assessed, 68% are in a threatened category (EW, CR, EN, and VU). This high proportion of threatened species may reflect the vulnerability of the palm family caused by the massive habitat loss that tropical ecosystems are facing (Myers et al. 2000). Typically each country also has its own national red list of threatened species and these often follow the guidelines of the IUCN (Llamozas et al. 2003; Calderón et al. 2005). In Paraguay the Secretariat of Environment (SEAM) updated the national list of threatened species in 2006 (Resolución 524/06) classifying the palm Butia marmorii as critically endangered. However the palm has not been yet included in the IUCN Red List as an assessed species.

Butia marmorii Noblick, 2006, is an acaulescent palm, with small grass-like leaves, and purple inflorescences at ground level (Images 1 & 2). The species is found in subtropical savanna like vegetation known as Cerrado. To date it is known only from two adjacent populations in the vicinity of Itakyry, Department of Alto Paraná, Paraguay, and a single Argentinean record (Noblick 2006) (Fig. 1), but its presence in Brazil (Três Lagoas, Mato Grosso do Sul) was postulated based on photographic records (Noblick 2006). Recent revisions however show that the Brazilian population is not the same species and the Argentinian population no longer exists (Lorenzi et al. 2010; Soares 2015). This makes the species endemic to Paraguay. Gauto et al. (2011) classified Butia marmorii as endangered due to its estimated area of occupancy highlighting other possible locations where the species may occur. Nevertheless, the threat of the loss of its natural habitat put the known population in high risk of extinction as eastern Paraguay has lost more than 50% of its natural vegetation cover in the last 50 years (Huang et al. 2009). In addition to this dramatic loss, the species occurs at low densities, is very inconspicuous, and inhabits isolated patches of Cerrado surrounded by soybean plantations. These characteristics make this species extremely vulnerable to any disturbance of its small area of remnant habitat. The areas where Butia marmorii occurred when it was described are not under legal protection (Noblick 2006).

Most of the biological traits of B. marmorii remain unknown, and the few scientific references that exist deal with descriptions and distribution (Pintaud et al. 2008; Stevens 2014; Soares 2015), and a historic anecdotal narration by Noblick (2014). Hoffmann et al. (2014) provided a summary of studies on the genus, highlighting the lack of information available for B. marmorii. The genus Butia itself, in fact, is poorly studied in general, as it is one of the less important palm genera from an economic point of view (Bernal et al. 2011). Soares (2015) made an important contribution to understanding the systematics of the genus, and mentioned the presence of B. marmorii only in Paraguay. No information about its rate of growth, its reproductive biology or its soil or nutrient requirements is available for the species, although cultivated specimens from the wild have been grown by institutions such as Montgomery Botanical Center (Griffith 2010), and Jardim Botânico Plantarum (http://www.plantarum.org.br/pagina/menus/125/Acervo_Vivo-Dezembro-2011.pdf), and Itaipu Binacional (Irene Gauto, pers. obs.), to ensure the survival of this evolutionary linage.

In order to better understand the threats that a species is facing, it is important to know its real distribution, the density of its populations, and its structure. Distribution models based on physical and ecological characteristics are a useful tool to highlight potential distribution areas of a species, as did Gauto et al. (2011) for B. marmorii. But more precise tools, such as small-scale satellite imagery classification of suitable habitat can show more accurate areas were a species could be found. These results can be verified in situ in order to better understand the real distribution of a species and its current threats in the wild.

In this work, we identify new areas of distribution for Butia marmorii, assessing the ecological status of each population recorded.

 

 

Materials and Methods

 

Potential distribution assessment

Gauto et al. (2011) made an extensive analysis of the distribution of Paraguayan palms stating that based on a spatial prediction, Butia marmorii is the Paraguayan palm with the most limited distribution, after the almost extinct Trithrinax brasiliensis var acanthocoma. Working on the hypothesis that the distribution of this palm must be wider than is currently known, we performed a fine-scale analysis of satellite images. In order to accomplish this, we made a supervised classification and visual interpretation of satellite images, in conjunction with a multi-temporal analysis using the sensors Landsat 1-MSS,5-TM,8-OLI, for the years 1973, 1984, 2002, 2012 and 2013.

The analysis was limited to the “area of occupancy” proposed by Gauto et al (2011), in the Alto Paraná Department (eastern Paraguay). A key factor for the analysis was the identification of Cerrado ecoregion, with which the species is strongly associated. The natural habitats of Alto Paraná are, however, highly disturbed, and it can be difficult to distinguish between natural Cerrado and deforested areas. Consequently, images from 1973 and 1984 were used to identify the historical distribution of the Cerrado, and more recent images to assess changes. The satellite image processing for the years 1973–1984 (120m resolution) was performed employing unsupervised classification methods to identify the areas of the potential presence of the palm using the two sites of known presence as a reference point. We then made a visual interpretation to improve the quality of results, in conjunction with an ASTER ASTGTM2 radar image to eliminate areas located in potentially flooded areas since the palm only occurs in highlands (Fig. 2). Finally, we identified the remaining fragments of habitat with a high probability of housing additional populations, through analysis of Landsat Images from the 2012–2013 (30 m of resolution), along with IKONOS and QuickBird high resolution images from Google Earth.

Once the map of potential distribution areas was available, field verification was performed to confirm the species presence or absence.

 

In situ population assessment

The verification of the presence of Butia marmorii in potential areas of occurrence was made with a series of fieldtrips. In localities where the palm was found to be present, we performed a survey to assess the population density and the ecological characteristics.

In each locality, 1ha plots were demarcated, divided into 25 sub-plots of 20×20 m (Dallmeier 1996). The spatial distribution of the 25 sub-plots was not necessarily squared (but maintaining the 400 m²), and the disposition was designed for the best fit with the spatial distribution of the palms and its environment. In each sub-plot, the following data were collected: GPS point, number of specimens, phenology status, soil type, soil coverage density, and associated plant species by surveys in the sub-plots.

 

Results

 

 

Distribution assessment

A total of 27 polygons were suggested as potential areas of occurrence of the endangered palm Butia marmorii (Fig. 3). All of them were in the northern Alto Paraná Department. The total surface area of these areas was approximately 18.12km2 (Table 1).

In situ verification confirmed that several of these localities had already been modified and cleared for crops (mostly soybean). In fact, most of the proposed localities were on farmlands, or in areas with severe environmental modification (Table 1). Thirty-five per cent of the suggested localities could not be closely visited because they were in private land and not authorization could be obtain. Butia marmorii populations were identified in sites 1, 8, 12, and 17 (Fig. 4). Of these four sites, only 1 and 8 showed ecological characteristics that could be analyzed, as they exhibited the lowest degree of environmental disruption. Site 12 corresponded to a growing area, where only a few isolated individuals were found, left by the owner of the establishment. Site 17 is a historical collection locality, with a marked reduction of original coverage caused by strong anthropogenic impact. Anthropogenic impacts through time are clearly visible through satellite analysis (Fig. 4) and are proof of habitat reduction for Butia marmorii (Table 2).

Population assessment

We observed an elevated degree of habitat alteration in Cerrado ecosystems where Butia marmorii occurs. Most of the original habitat had been converted into mechanized-agriculture or, to a lesser degree, forestry plantations of exotic species.

The parameters and characteristics of the two populations with less anthropogenic impacts are presented below; but given the lack of formal protection these do not have any greater chance of long term survival than any other localities.

- Site 1: Locality of first collections. Surface of vegetation = 5.8 hectares. Private property in disuse, with significant anthropogenic impact. Individuals = 1142 (density = 0.11 individuals/m2) (Appendix 1). Individuals reproductively active with flowers, fruits or both together. Mostly sandy soil, reddish, with formations of savannas, grasslands, or secondary forest. Figure 6 shows the composition and floristic diversity (at the family level) for the site. The list of associated species in this site is presented in Appendix 1.

- Site 8: Natural area with moderate anthropogenic impact. Surface of vegetation = 16.6 hectares. Individuals = 552 (54 Butia marmorii, 180 B. paraguayensis, and 318 Butia sp. (sterile specimens)). Butia marmorii density was 0.0054 individuals/m2 (Appendix 1). Individuals reproductively active (with flowers/fruits) were found. Mostly clay soil, reddish, with formations of savanna associated shrubs. Figure 6 shows the floristic composition (at the family level) for the site. The composition of the flora and characteristics of this site are presented in Appendix 1.

Sites 12 and 17 held a very low population of Butia marmorii with the highest recorded population of just 20 individuals (Site 12), 15 of which were in a tilled area.

On sites 2, 7 and 12 were found specimens of Butia paraguayensis and some sterile specimens that could not be identified.

Discussion

 

Species distribution models are powerful tools used in biological conservation, and can be used to predict not only the actual distribution of an organism, but also to infer distribution over time and assess how environmental change might affect that chorology (Theurillat & Guisan 2001; Williams et al. 2003; Thomas et al. 2004). The utility of these programs has been demonstrated numerous times (Carpenter et al. 1993; Loiselle et al. 2003; Naoki et al. 2006), but the predictions are never completely accurate as they work with climatic layers, and the programs do not distinguish the presence of cities or deforestation. Gauto et al. (2011) presented a distribution model for Butia marmorii that is extended northwards to Canindeyú and Amambay departments (Fig. 5c in Gauto et al. 2011). The technique employed here however identifies small and fragmented areas as potential localities of occurrence, as it also incorporates information on land use change.

Through an a posteriori and in situ verification, new records for Butia marmorii, at least two new sites (Sites 8 and 12), are documented. This is important for our understanding of the distribution of B. marmorii in the country. No additional populations of this rare species have been recorded since the species was described (Noblick 2006; Gauto et al. 2011). Gauto et al. (2011) categorized this species as Endangered (“EN” following the IUCN criteria) given the reduced area of occupancy. In addition, here we confirm that the species is threatened by deforestation and rapid changes in land use, and that its distribution is fragmented and restricted to increasingly smaller patches. We quantified habitat loss, and just 14% of the original area of occurrence remains today (Table 2, Fig. 4). Such a decline is illustrated in Site 1, the type locality described by Noblick (2006), and which holds the highest number of individuals (Fig. 7). It is possible to see the patch of Cerrado (darker green area in the center of Fig. 7A) located in the southern extreme of Site 1, and its reduction through time due to anthropic intervention (Fig. 7B–D). Hence, we found that the situation of this palm is even worse than depicted by Gauto et al. (2011). In view of its extent of occurrence (EOO) of less than 100km2, its severely fragmented distribution, and the continuing decline in the extent and quality of its habitat, now we consider Butia marmorii as Critically Endangered CR B1ab(i,ii,iii,iv,v) (Appendix 2) following IUCN categories and criteria (IUCN 2012).

In two places we were able to calculate the population density of the species, finding significant differences between the two sites. Butia marmorii density is significantly higher in Site 1, than in Site 8, even when in both sites the two Butia species share habitat. The density of B. paraguayensis in Site 1 was extremely low, whereas in Site 8 it had a higher density (180/ha) than B. marmorii (54/ha). This is a first approach to the knowledge of the ecology of the species and their ecological relationships with other species. The next step is a detailed analysis of environmental conditions to infer the reasons behind the differing density. No previous studies have focused on the estimation of population density in Butia grass-like palms, but estimations of Butia palm trees (Guilherme & Oliveira 2010; V.V.F. Lima 2011, unpub. data) are predictably smaller than our results given the greater size of Butia palm trees.

In these localities some individuals show intermediate characteristics between B. marmorii and B. paraguayensis, making it difficult for identification in the field; thus specimens with fertile parts were collected and identified afterwards. More detailed taxonomic studies are thus recommended to better understand the systematics of the genus.

A future molecular approach should also be carried out. Given that the area where B. marmorii is present is being rapidly reduced, the chance of panmixis is also reduced, and populations are becoming more isolated. It is alarming that the palm tree Butia eriospatha has a low genetic diversity even in a panmitic population (Nazareno & dos Reis 2012), and that smaller populations are more vulnerable to genetic drift (Nazareno & dos Reis 2014). Needless to say populations of B. marmorii are extremely reduced and urgent and diverse actions are required in order to preserve this linage.

 

 

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