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.