4.1 How do bioclimatic variables influence taxonomic, and phylogenetic diversities, and the phylogenetic structure in the tropical forests of a river basin (TFRD)?
Water regime drives species richness and phylogenetic community structure in the TFRD more than other types of environmental variables. At least one among annual precipitation, water excess duration, water excess severity, and water deficit severity were significant in all averaged models, except for the model for sesMNTD. Species richness, sesPD, sesMPD and percentage of zoochory were affected by water excess duration. All dispersal types were explained partially by water excess severity. Temperature regime was the second mst important important regime. Maximum temperature of the warmest month and isothermality explained sesMNTD. Maximum temperature of the warmest month, and temperature seasonality explained partially species richness. Among the variables, water excess duration, annual precipitation, maximum temperature and isothermality influenced the phylogenetic diversity and phylogenetic structure. The effects of temperature on richness, and on sesMNTD suggest environmental filtering effects causing phylogenetic clustering driven by decreasing maximum temperature of the warmest month and decreasing isothermality (i.e., increasing temperature variation). Therefore, the lower temperature and the less temperature variation in different seasons, the more environmental filtering.
The percentage of species with zoochory, anemochory or autochory were related to phylogenetic structures (i.e., sesMPD) in different ways. Increasing zoochory increases phylogenetic distances between species (i.e., increasing sesMPD) meanwhile increasing anemochory, and autochory decrease phylogenetic distances between species (i.e., decreasing sesMPD). The opposite relation of zoochory with sesMPD was not because zoochory is convergent, but because the less zoochory, the more abiotic dispersion (i.e., anemochory + autochory) that is clustered for MPD (i.e., DispersalNRI more related than by chance), suggesting anemochory, and autochory as homologies in the TFRD metacommunity. Only zoochory decreased with increasing water excess severity, and appears to be the only dispersal type benefited with increasing water surplus. Water excess severity was positively related to anemochory, and autochory, and might be interpreted as stresses influencing positively these dispersal types. Water deficit severity influenced negatively autochory.
The answer of the first question shows how environmental variables influence taxonomic, and phylogenetic diversities as well as phylogenetic structure in the tropical forests of that large river basin (TFRD). Seven environmental variables were found to influence the taxonomic diversity, phylogenetic diversity and phylogenetic structure in averaged models: water excess duration, water excess severity, water deficit duration, water excess severity, maximum temperature, temperature seasonality, and isothermality. As water excesses and water deficits increase in number of days, the species richness decreases. As the maximum temperature and the temperature seasonality decrease, the species richness decrease. Thus, more days of water excesses or more days of water deficits in TFRD are associated with loss of species richness as well as lower maximum temperatures and lower temperature variation between seasons. Therefore, the found global model shows that increasing the number of days with excess or deficit of water, decreasing temperatures, and decreasing temperature variation, decrease species richness.
Still answering the first question, as annual precipitation decreases and there are more days of water excess, sesPD and sesMPD increase; as maximum temperature and isothermality increase, sesMNTD increases. Thus, the lower annual precipitation, the more water excess days, the higher temperature variation, and the higher maximum temperatures in TFRD, the greater the phylogenetic diversity and phylogenetic distances between species. However, as the more days with water excess (i.e., days with higher precipitation than evapotranspiration) cause higher sesPD and sesMPD, it is possibly because benefits the zoochory that is positively-related to mean phylogenetic distances (see zoochory discussion below). Therefore, higher precipitation promotes decreasing sesPDs and sesMPDs (i.e., phylogenetic clustering) in the TFRD similarly to effects of environmental filters found in tropical vegetation (Gastauer and Meira-Neto 2013; Miazaki et al. 2015), but does not cause species richness loss. Phylogenetic effects in tropical vegetation that can be explained by plant-plant interactions, density-dependence effects (Paine et al. 2012; Kraft et al. 2015; Carrión et al. 2017; Cadotte and Tucker 2017; Meira-Neto et al. 2018), and environmental filtering that has been reported as cause of phylogenetic effects in many different groups of species, especially plants. For instance, environmental filtering promotes phylogenetic effects in protists, in diatoms (Leibold et al. 2010; Singer et al. 2018; Keck and Kahlert 2019), and likely causes phylogenetic clustering in plant communities of tropical forests when associated with species richness decreasing (Gastauer and Meira-Neto 2013; Parmentier et al. 2014). Therefore, the increasing annual precipitation in the TFRD that shortens phylogenetic distances might be an environmental filter effect because of excessive water. High precipitation may cause temporarily flooding stresses (Bueno et al., 2014; Pontara et al., 2016), and, consequently, may filter out lineages without conserved traits of flooding tolerance, but species richness does not decreased with the increasing annual precipitation. Alternatively, increasing annual precipitation would promote competition, and/or density dependent effects. For instance, high precipitation might cause competition increasing, and higher density-dependent effects by increased water resources and increased plant growing (see Tilman 1988). However, the forests with largest trees in TFRD, which would indicate stronger competition, are in low altitude sites with lower precipitation (Lopes et al. 2002; Camargos et al. 2008; Souza et al. 2012, 2013). The only clear result is that as precipitation increases, PD, and MPD decrease as an effect of increasing percentages of species with abiotic dispersion (see dispersal discussion below). Therefore, environmental filtering, competition and density dependent effects do not explain the PD and the MPD variation in TFRD. On the other hand, temperature regime can explain environmental filtering because species richness and sesMNTD decrease as maximum temperature decreases, indicating that the lower the maximum temperature, the closer the relatives in the TFRD communities and the lower the species density. High and low temperatures have been reported as environmental filters in forests, but high temperatures are rather filters in tropical dry forests, and low temperatures are rather filters associated with high altitudes or latitudes in temperate forests (Qian et al. 2014; Qian 2018). Therefore, our results suggest that the seasonal TFRD are environmentally filtered by low temperatures that cause decreasing species richness, and decreasing phylogenetic distance between species of their communities by filtering in species with conserved traits within phylogenetic lineages.
4.2 How do environmental variables, phylogenetic structure and the main types of seed dispersal relate to each other in the TFRD assemblages?
The percentage of species with zoochory, anemochory and autochory was significantly related to sesMPD and not to sesMNTD or sesPD, which means that the main association of dispersal types with the communities’ phylogenies is throughout the entire phylogenetic tree (i.e., sesMPD). As the DispersalNRI is clustered for abiotic dispersal types, the clustered sesMPD reinforce that anemochory and autochory are conserved in phylogenetic branches originated in old nodes congruently with the decreasing sesMPD as anemochory and autochory. As a consequence, the increasing proportion of zoochory is not caused by its preeminence as homoplasy in the TFRD metacommunity, but because abiotic dispersal decreases. Thus, increasing anemochory and autochory reduce the sesMPD distances between species congruently with their clustered DispersalNRI in the TFRD metacommunity.
Zoochory is phylogenetic clustered towards the tip of phylogenetic tree according to its DispersalMNTD. That means the species with zoochory are predominantly clustered in lineages with conserved zoochory diversified from recent nodes. Despite zoochory is clustered towards the tip of phylogenetic tree, zoochory is not clustered throughout the entire phylogenetic tree. Anemochory is also clustered clustered according to its DispersalMNTD. Autochory is not clustered towards the tip of phylogenetic tree in TFRD, suggesting lack of recent diversification of lineages with conserved autochory.
The dispersal types responded to water regime. The dominant dispersal type in TFRD is zoochory that varies from 50% up to more than 95% of the tree species in evergreen and seasonal Atlantic Tropical Forests (Tabarelli and Peres 2002). In the TFRD, the minimum zoochory percentage found in a forest was 53% and the maximum was 81% (data not shown). As dominant dispersal type, zoochory responded positively to water excess duration, and water deficit severity meanwhile anemochory and autochory were not influenced by those explaining variables. However, zoochory responded in an opposite way from the two abiotic dispersal types to water excess severity. Zoochory also responded in an opposite way from autochory to water deficit severity. Thus, zoochory seems to be impaired meanwhile anemochory and autochory seem to be benefitted in sites with extreme severity of water excess or water deficit.
As anemochory and autochory are clustered in some phylogenetic branches in the TFRD metacommunity, the presence of these dispersal types in restored TFRD will allow those species to improve the functional and phylogenetic diversity of restored forests by representing entire phylogenetic branches, especially in those TFRD with extreme water regimes (i.e., high severity of water excess, and high severity of water deficit). Therefore, the relation between severity of water excess, and severity of water deficit with the two abiotic dispersal types deserves attention since extreme water regimes are increasing according to forecasted climate scenarios in the most of the Atlantic Forest distribution (IPCC 2013). As a consequence, the proportion of anemochory and autochory may increase in the TFRD during the next decades in a global change scenario.
4.3 What of the answers to the previous questions can be used in the ecological restoration of TFRD in a global change scenario, as well as in the conservation of biodiversity and ecosystem services?
Species selection is not the restoration project itself. Most selected species may not be able to thrive under the harsh initial conditions of the restoration sites. This means that the selected species must be used in TFRD restorations to add taxonomic and phylogenetic diversity in order to improve the suitability and long-term stability of the restored ecosystems. For that, our databank delivered as supplementary material will offer the basis for the species selection. The results sequence shows how the TFRD community assembly rules are central to the species selection for the planned large-scale restoration in the basin, which includes mitigating the Mariana disaster that compromised the service of water purification in the basin. 1) The environmental filtering promoted by low temperatures (i.e., low maximum temperatures) drops the taxonomic diversity shortening the phylogenetic distance between species, predominantly filtering in species of some recently diversified lineages. Temperatures in TFRD are also related with altitude (data not shown). Thus, the use of some lineages better fitted for TFRD restoration in sites with low maximum temperatures (i.e., high altitudes inside the basin) should enhance the performance of restored forests. 2) Possibly the water purification is the most affected ecosystem service by the main players of global change, such as forests degradation, agriculture (Cabel et al. 1982), urbanization (Zhao et al. 2013), and environmental disasters (Lambertz and Dergam 2015; Meira et al. 2016; Meira-Neto and Neri 2017). Water purification should be restored in all regions of the basin through forest restoration. We understand that tree species with good fitness to the bioclimatic profiles of restored sites will enhance the ecosystem service of water purification, especially in areas with low maximum temperature, and high annual precipitation, improving the functioning and the stability of restored forests (Cadotte et al. 2009, 2012; Isbell et al. 2015; Brancalion et al. 2017). 3) In a global change scenario that predicts increasing climate variance for TFRD (IPCC 2013), the inclusion of species with anemochory and autochory in restoration practices increases functional and phylogenetic diversity when associated with a large proportion of species with zoochory, especially in areas with current or predicted extreme water excess or extreme water deficit. 4) A large proportion of species with zoochory in restored forests is mandatory because it assembles communities with high taxonomic, and phylogenetic diversity with the cobenefit of carbon stock (Matos et al. 2020), conserving dispersal services (Tabarelli and Peres 2002; Jansen et al. 2014), conserving dispersers, and conserving the threatened ecological interactions of tropical forests (Janzen 1986).