Coastal Dune Vegetation Dynamism and Anthropogenic-Induced Transitions in the Mexican Caribbean during the Last Decade.

In the Mexican Caribbean, environmental changes, hydrometeorological events, and anthropogenic activities promote dynamism in the coastal vegetation cover associated with the dune; however, their pace and magnitude remain uncertain. Using Landsat 7 imagery, spatial and temporal changes in coastal dune vegetation were estimated for the 2011-2020 period in the Sian Ka'an Biosphere Reserve. The SAVI index revealed cover changes at different magnitudes and paces at the biannual, seasonal, and monthly timeframes. Climatic seasons had a significant influence on vegetation cover, with increases in cover during northerlies (SAVI: p = 0.000), while the topographic profile of the dune was relevant for structure. Distance-based multiple regressions and redundancy analysis showed that temperature had a significant effect (p < 0.05) on SAVI patterns, whereas precipitation showed little influence (p > 0.05). The Mann-Kendall tendency test indicated high dynamism in vegetation loss and recovery with no defined patterns, mostly associated with anthropogenic disturbance. High-density vegetation such as mangroves, palm trees, and shrubs was the most drastically affected, although a reduction in bare soil was also recorded. This study demonstrated that hydrometeorological events and climate variability in the long term have little influence on vegetation dynamism. Lastly, it was observed that anthropogenic activities promoted vegetation loss and transitions; however, the latter were also linked to recoveries in areas with pristine environments, relevant for tourism.

Ecological niche modeling of coastal dune plants and future potential distribution in response to climate change and sea level rise.

Climate change (CC) and sea level rise (SLR) are phenomena that could have severe impacts on the distribution of coastal dune vegetation. To explore this we modeled the climatic niches of six coastal dunes plant species that grow along the shoreline of the Gulf of Mexico and the Yucatan Peninsula, and projected climatic niches to future potential distributions based on two CC scenarios and SLR projections. Our analyses suggest that distribution of coastal plants will be severely limited, and more so in the case of local endemics (Chamaecrista chamaecristoides, Palafoxia lindenii, Cakile edentula). The possibilities of inland migration to the potential 'new shoreline' will be limited by human infrastructure and ecosystem alteration that will lead to a 'coastal squeeze' of the coastal habitats. Finally, we identified areas as future potential refuges for the six species in central Gulf of Mexico, and northern Yucatán Peninsula especially under CC and SLR scenarios.

Comunidade de abelhas (Hymenoptera, Apoidea) em ecossistema de dunas na Praia de Panaquatira, São José de Ribamar, Maranhão, Brasil / Community of bees (Hymenoptera, Apoidea) in the coastal sand dunes at Panaquatira beach, São José de Ribamar, Maranhão, Brazil

Comunidade de abelhas (Hymenoptera, Apoidea) em ecossistema de dunas na Praia de Panaquatira, São José de Ribamar, Maranhão, Brasil. Foi analisada a estrutura da comunidade de Apoidea de uma área restrita de dunas primárias em São José de Ribamar, Maranhão, Brasil. Amostragens foram realizadas quinzenalmente durante um ano com metodologia padronizada totalizando 24 coletas. As coletas ocorreram no período das 12:00 às 18:00 h no primeiro dia e das 6:00 às 12:00 h no segundo, realizadas por dois coletores. Um total de 3305 indivíduos de 31 espécies pertencentes a quatro famílias (Apidae>Halictidae>Megachilidae>Andrenidae em número de indivíduos) foram coletadas nas flores. Centris com 14 espécies e 890 indivíduos foi o gênero mais rico e abundante. O padrão de abundância e riqueza foi bastante semelhante ao de outros habitats de dunas no nordeste brasileiro. Das espécies amostradas, 61 por cento foram representadas por menos de 36 indivíduos e apenas 5 espécies foram muito abundantes com mais de 177 indivíduos: Apis mellifera Linnaeus, Centris (Centris) leprieuri Spinola, Eulaema (Apeulema) nigrita Lepeletier, Eufriesea surinamensis Linnaeus e Xylocopa (Neoxylocopa) cearensis Ducke. As abelhas estiveram presentes durante todo o ano, apresentando picos de abundância no período de maior precipitação. A atividade diária foi maior entre 06:00 e 11:00 h, quando a temperatura aumentava e a umidade relativa decrescia.

The community structure of Apoidea of a restricted area of primary dunes in São José de Ribamar, Maranhão, Brazil was analyzed. Standardized samples were taken for one year, 2 times a month, from 12:00 a.m. to 6:00 p.m. on the first day and from 6:00 a.m. to 12:00 a.m. on the second by two collectors. A total of 3305 individuals of 31 species, belonging to four families (Apidae > Halictidae > Megachilidae > Andrenidae) were collected. Centris with 14 species and 890 individuals was the richest and most abundant genus. The abundance pattern and the richness were very similar to other sand dunes habitats in northeast Brazil. Of the total of bees sampled, 61 percent were represented by less than 36 individuals. The five most abundant species (more than 177 individuals) were: Apis mellifera Linnaeus, Centris (Centris) leprieuri Spinola, Eulaema nigrita Lepeletier, Eufriesea surinamensis Linnaeus and Xylocopa (Neoxylocopa) cearensis Ducke. Bees were active throughout the year, with abundance peaks in the highest rainfall periods. Daily activity was greatest between 06:00 and 11:00 a.m., when relative humidity decreased and the temperature increased.

Sampling spatial and temporal variation in soil nitrogen availability.

There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+4) and nitrate (NO-3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH+4 and NO-3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+4 and NO-3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+4 and NO-3 concentrations decreased with the age of the dune. Soil NO-3 concentration showed strong spatial structure, but soil NH+4 concentration was not spatially structured. Plant-available NH+4 and NO-3 showed relatively little spatial structure: only NO-3 availability in the second sampling period had significant patch structure. Spatial maps of NH+4 and NO-3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO-3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO-3 concentrations, providing some evidence that patches of plant-available NO-3 may reappear at the same spatial locations at irregular points in time.