Impact of human activities on the geographical distribution pattern of Orchids
Human actions are causing a biodiversity crisis (Brooks et al., 2006), which is a vital threat factor emphasized in most orchid conservation research (Acharya et al., 2011; McCormick & Jacquemyn, 2014; Zhang et al., 2015). Nevertheless, there are no exact approaches to evaluate the impact of human activities on the geographical distribution of orchids. In our study, we quantified human activities using spatially explicit factors such as grazing, roads, and land use, which proved effective in improving the accuracy of the orchid SDMs. Meaning that human activity can be used as a predictor of limiting species dispersal and will reflect a more realistic potential geographic distribution of orchids, which was also demonstrated in our suitability maps: the suitable area without the hi factor tended to be higher than the predicted area with the factor included. Of course, we also note the lack of enough significance in this to suggest that human activities are not the primary environmental variable driving the geographic distribution of orchids in the Hengduan Mountains. Our investigated phenomenon precisely coincided with this view: a part of the orchid populations was found in fragmented forest patches close to towns.
What causes this phenomenon? Orchids generally occupy a relatively small ecological space and require more microenvironment (Djordjevic et al., 2020). As a result, they can survive on a small habitat patch, even if hardly. Such situations are not uncommon. In Costa Rica, several orchid hotspots still include some less primitive artificial environments, such as coffee plantations (Crain & Fernandez, 2020). Additionally, the orchids distribution pattern cannot be separated from the mycorrhizal environment dependent on the vegetation type (Selosse et al., 2004). Fortunately, with the improvement of people’s awareness of ecological and biodiversity protection, the possibility of a specific habitat or vegetation completely disappearing due to human activities is reduced extremely. Physiologically, tiny, numerous, and long-distance transmission capability seeds make orchids overcome some geographical obstacles, as we observed that most orchid populations show a highly dispersed spatial distribution pattern, which could resist disturbance caused by sudden environmental changes from human activities and affect little the geographical distribution pattern and the regional species pool. However, for some specific groups, the impact of human activities is crucial. Due to long-term illegal collection, the wild individuality of Gastrodia R. Br., Dendrobium Sw., Cymbidium Sw., etc. has experienced drastically reduced. Some endangered orchids with high environmental specificity, distribute narrowly, and their endangerment mechanism is unclear. If the only habitat is inadvertently destroyed by human activities, which will lead to species extinction and loss of biodiversity.
However, the impact of interference is not all adverse. Djordjevic et al. suggests that some degree of disturbance has a positive effect on orchid performances by creating a space with favorable lighting conditions (Djordjevic et al., 2020). The study by Jacquemyn et al. illustrates forest coppicing maintains viable populations of Orchis mascula in the long term (Jacquemyn et al., 2008). Considering pollinator diversity and reproductive success, Rewicz et al. proved roadside verges and edges of forests are better than those farther from the edges and roads exampling Epipactis helleborine (Rewicz et al., 2017). It is still worth noting that the distribution and germination of orchids are usually limited by the fungal distribution, at the same time, most orchids flowers belong to deceptive pollination, and their pollination system is fixed and single (Givnish et al., 2015; Kelly et al., 2013; McCormick & Jacquemyn, 2014; Tremblay et al., 2005). Accordingly in the ecology niche, it’s not easy to see orchids predominate in a certain habitat due to their competitiveness may be weaker than other species (Fekete et al., 2019). There is reason to believe that opportune interference may provide an ecological opportunity for orchids sometimes, which explains why most of the orchids are distributed in forest windows or beside the trails. From the perspective of the ecological landscape, environmental heterogeneity plays an important role in the diversity, differentiation, and rapid formation of orchid species (Perez-Escobar et al., 2017), but does the landscape heterogeneity created unintentionally by human beings have the same effect? This needs further study.
Although human activities do not seem to produce much of a role in our model, we provide an available method for conservation managers in SDMs when they need to quantify human interference, with interchangeable choices of indicators for different purposes. For some specific regions or species, we cannot deny that human activities are probably the primary causes affecting their geographic distribution pattern.