Spatial ecology deals with the spatial distribution of organisms and a general objective of spatial analysis is to reveal the relationship between observed spatial distributions of species and the mechanisms underlying these spatial distributions. The recent advances in analysing spatial patterns of organisms in spatial ecology have greatly contributed to better understanding the distribution of organisms in space and time.
A prerequisite for exploring the ecological information provided by spatial distributions of organisms is to precisely describe the spatial structure of point patterns with statistical methods. Over the past decades, statisticians have developed structurally different summary statistics for this purpose. Moreover, rapid advances in computer science and technology have resulted in an increased application of spatial statistics. In addition, development of remote sensing and geographic information system (GIS) technology has led to the identification of spatiotemporal patterns of organisms and has increased the possibility to identify how human activities have influenced animal and plant habitats. Consequently, ecologists have started to introduce spatial variation and complexity of ecosystems into their analyses, including changes of spatial patterns over time.
The widespread application of spatial analysis in ecological studies makes it possible to consider special parts in IALE World Congresses or related topics in IALE Annual Conferences and prepare special issues to be published by technical journals (e.g., Ecological Modelling, Spatial Statistics).
Letter from the Working Group leader
One of the most outstanding activities of our WG in 2019 was studying the mixed stands of tropical rainforests encroached by a tree species. The tropical rainforests are one of the most important biomes and known as the lungs of the earth. The forests have the greatest biodiversity and mainly found in South America, Central Africa and Southeast Asia. Some parts of the forests found in Vietnam suffer from illegal logging by local people. These resulting gaps facilitate the spatial distribution of invasive species. One of the species, i.e. Streblus macrophyllus Blume (Moraceae) (S.m.), can be observed not only in the mixed forests of Vietnam but also in China, Indonesia, Malaysia, and Philippines. This species is established in gaps and quickly encroaches into stands and changes the spatial structure of forests. It inhibits other species and reduces their natural regeneration which leads to a decrease of biodiversity. We, therefore, aimed to investigate the spatial structure of the tropical rainforest communities encroached by S.m. We studied three forest stands with different levels of S.m. encroachment. To follow our objective, three fully mapped 1-ha plots were established in Cucphuong National Park in northern Vietnam. Methods of phylogenetic community and nearest neighbour statistics were applied to identify how community structure changes with S.m. encroachment. Results showed that phylogenetic distance, phylogenetic diversity and mean phylogenetic distance increased with increasing species diversity and decreasing S.m. abundance in the forest communities. Net related index values were positive indicating a clustered phylogenetic structure among all sampled forest communities. S.m. trees were well mixed with its heterospecifics and had regular to aggregated distributions, while the species showed evidence to be a strong competitor to its neighbours. Competition could be major ecological process that regulates forest communities encroached by S.m. and could result in regular spatial distribution of heterospecifics.
One of the main activities of our WG in 2020 was the integration of remote sensing in spatial ecology. Remote sensing is a fast growing science and technology that can play an important role in vegetation ecology from landscape to local scales. Remote sensing which is guided by unmanned aerial vehicles (UAVs) is a reliable tool to survey structurally different ecosystems, particularly in arid and semi-arid ecosystems with sparse vegetation cover across large spatial scales. UAVs have the potential to be efficiently applied in spatial ecology of plants, behavior of target moving species, the spread of invasive species, and status of threatened species. Despite the importance of UAVs in ecology, the various applications in semi-arid environments have been less assessed. To address this gap in spatial ecology, we used UAV-derived point clouds to map two plant species in a semi-arid region and study their intra- and interspecific interactions in order to explore the underlying processes that result in their spatial aggregation at landscape levels. Our results indicated that the UAV point clouds could map all 200 randomly selected species individuals and identify their species type with an accuracy of 92%. Univariate and bivariate forms of summary statistics in spatial ecology were implemented to detect the intra and interspecific interactions of the species. We observed the aggregation of the species individuals in clusters of conspecifics and heterospecifics at small spatial scales, most likely as a result of environmental heterogeneity, intense intraspecific facilitation, and weak interspecific mutualism. Our findings demonstrated that promising UAV photogrammetric data can be efectively utilized by ecologists for investigation of plant associations in semi-arid regions in order to explore the underlying mechanisms and processes.
Yousef Erfanifard, PhD (WG leader)