Dynamic Landscape Fragmentation and the Driving Forces on Haitan Island, China

Island ecosystems have distinct and unique vulnerabilities that place them at risk from threats to their ecology and socioeconomics. Spatially exhibiting the fragmentation process of island landscapes and identifying their driving factors are the fundamental prerequisites for the maintenance of island ecosystems and the rational utilization of islands. Haitan Island was chosen as a case study for understanding landscape fragmentation on urbanizing Islands. Based on remote sensing technology, three Landsat images from 2000 to 2020, landscape pattern index, transect gradient analysis, and moving window method were used in this study. The results showed that from 2000 to 2020, impervious land increased by 462.57%. In 2000, the predominant landscape was cropland (46.34%), which shifted to impervious land (35.20%) and forest (32.90%) in 2020. Combining the moving window method and Semivariogram, 1050 m was considered to be the best scale to reflect the landscape fragmentation of Haitan Island. Under this scale, it was found that the landscape fragmentation of Haitan Island generally increased with time and had obvious spatial heterogeneity. We set up sampling bands along the coastline and found that the degree of landscape fragmentation, advancing from the coast inland, was decreasing. Transects analysis showed the fragmentation intensity of the coastal zone: the north-western and southern wooded zones decreased, while the concentration of urban farmland in the north-central and southern areas increased. The implementation of a comprehensive experimental area plan on Haitan Island has disturbed the landscape considerably. In 2000, landscape fragmentation was mainly influenced by topography and agricultural production. The critical infrastructure construction, reclamation and development of landscape resources have greatly contributed to the urbanisation and tourism of Haitan Island, and landscape fragmentation in 2013 was at its highest. Due to China’s “Grain for Green Project” and the Comprehensive Territorial Spatial Planning policy (especially the protection of ecological control lines), the fragmentation of Haitan Island was slowing. This study investigated the optimal spatial scale for analyzing spatiotemporal changes in landscape fragmentation on Haitan Island from 2000 to 2020, and the essential influencing factors in urban islands from the perspective of natural environment and social development, which could provide a basis for land use management and ecological planning on the island.

Biochar Rescues Native Trees in a Global Biodiversity Hotspot

Many tropical invasive species have allelopathic effects that contribute to their success in native plant communities. Pyrolyzed biomass (“biochar”) can sorb toxic compounds, including allelochemicals produced by invasive plants, potentially reducing their inhibitory effects on native species. Strawberry guava (Psidium cattleianum) is among the most important allelopathic invasive species in tropical islands and recognized as the most serious invasive species threat in the global biodiversity hotspot of Mauritius. We investigated the effects of additions of locally produced biochar on native tree species in a field experiment conducted in areas invaded by strawberry guava within Mauritius’ largest national park. Growth and survivorship of native tree species were monitored over 2 ½ years in plots subjected to four treatments: non-weeded, weeded, weeded + 25 t/ha biochar and weeded + 50 t/ha biochar. Native tree growth and survivorship were strongly suppressed by strawberry guava. Biochar treatments dramatically increased native tree performance, with more than a doubling in growth, and substantially increased native tree survivorship and species diversity, while suppressing strawberry guava regeneration, consistent with growth-promoting properties and sorption of allelochemicals. We conclude that biochars, including “sustainable biochars” produced from locally accessible biomass using low-tech pyrolysis systems, have considerable potential to counteract effects of allelopathic invaders and increase the capacity for native species regeneration in tropical island ecosystems.

Biodiversity of freshwater macroinvertebrates on Gökçeada Island (North Aegean Sea, Turkey)

Island ecosystems have attracted the attention of scientists since the early days of science because of their formation and biodiversity. Despite their abundant freshwater resources, data on freshwater diversity of Gökçeada are incomplete, especially for macroinvertebrates. This study was conducted in a wide range of freshwater ecosystems on Gökçeada between May 2016 and September 2018. Sampling of macroinvertebrates was performed using a hand net from 34 pre-selected sampling sites on the island. A total of 78 aquatic macroinvertebrate taxa were found, 46 of which are new records for the island. The most common species during the study were Gammarus komareki and Bythinella gokceadaensis with a frequency of 25.93%, followed by Tubifex tubifex, Gammarus sp. and Caenis sp. with a frequency of 22.22%. Endemic and invasive species on the island were assessed according to their presence and frequency values. Based on the results of the current study and previous data, it can be concluded that Gökçeada is characterized by a remarkable species diversity compared to aquatic macroinvertebrates on other Aegean islands.

Low-coverage reduced representation sequencing reveals subtle within-island genetic structure in Aldabra giant tortoises

Aldabrachelys gigantea (Aldabra giant tortoise) is one of only two giant tortoise species left in the world and survives as a single wild population of over 100,000 individuals on Aldabra Atoll, Seychelles. Despite this large current population size, the species faces an uncertain future because of its extremely restricted distribution range and high vulnerability to the projected consequences of climate change. Captive-bred A. gigantea are increasingly used in rewilding programs across the region, where they are introduced to replace extinct giant tortoises in an attempt to functionally resurrect degraded island ecosystems. However, there has been little consideration of the current levels of genetic variation and differentiation within and among the islands on Aldabra. As previous microsatellite studies were inconclusive, we combined low-coverage and double digest restriction associated DNA (ddRAD) sequencing to analyze samples from 33 tortoises (11 from each main island). Using 5,426 variant sites within the tortoise genome, we detected patterns of population structure within two of the three studied islands, but no differentiation between the islands. These unexpected results highlight the importance of using genome-wide genetic markers to capture higher-resolution genetic structure to inform future management plans, even in a seemingly panmictic population. We show that low-coverage ddRAD sequencing provides an affordable alternative approach to conservation genomic projects of non-model species with large genomes.

Keystone Species on New Zealand Offshore Islands: Ecological Relationships of Seabirds, Rats, Reptiles and Invertebrates on Cook Strait Islands

<p>The influence of seabirds and rats on island ecosystems was measured to assess the applicability of the keystone species concept for ecology and conservation. Pitfall trapping for lizards and small invertebrates, soil sampling and stable isotope analysis was used to assess the roles played by seabirds and rats on six islands in the Marlborough Sounds. Both abundance and ordinal richness of invertebrates were found to be greater on islands with seabirds than on seabird-free islands. Although lizard distribution was strongly influenced by species-specific habitat requirements, the greatest numbers of lizards recorded in this study were found on seabird-inhabited islands. Although significant differences were not found, the C:N ratio of soils in seabird colonies in this study and at other sites was lower than that at seabird-free sites. Nitrogen stable isotope analysis showed that a proportion of the diet of animals at a range of different levels throughout the island foodweb was derived from seabirds. Rats were found to negate many of the positive effects of seabirds. As well as significantly lower numbers of seabirds, islands with rats had lower abundance of lizards and lower abundance and diversity of mall invertebrates than rat-free islands. Although both seabirds and rats play important roles in island ecosystems, neither conformed to a definition of a keystone species. Theoretical and practical problems were found with the calculation of keystone status for different taxa. Given that important species cannot be shown to be keystones, and that calculation is technically difficult (and maybe impossible) the classification of seabirds, rats, or any other species as keystone is not likely to advance theoretical ecology or assist with conservation management. Attempts to define keystone species were found to be unsuccessful and abandonment of the term was advised.</p>

Keystone Species on New Zealand Offshore Islands: Ecological Relationships of Seabirds, Rats, Reptiles and Invertebrates on Cook Strait Islands

<p>The influence of seabirds and rats on island ecosystems was measured to assess the applicability of the keystone species concept for ecology and conservation. Pitfall trapping for lizards and small invertebrates, soil sampling and stable isotope analysis was used to assess the roles played by seabirds and rats on six islands in the Marlborough Sounds. Both abundance and ordinal richness of invertebrates were found to be greater on islands with seabirds than on seabird-free islands. Although lizard distribution was strongly influenced by species-specific habitat requirements, the greatest numbers of lizards recorded in this study were found on seabird-inhabited islands. Although significant differences were not found, the C:N ratio of soils in seabird colonies in this study and at other sites was lower than that at seabird-free sites. Nitrogen stable isotope analysis showed that a proportion of the diet of animals at a range of different levels throughout the island foodweb was derived from seabirds. Rats were found to negate many of the positive effects of seabirds. As well as significantly lower numbers of seabirds, islands with rats had lower abundance of lizards and lower abundance and diversity of mall invertebrates than rat-free islands. Although both seabirds and rats play important roles in island ecosystems, neither conformed to a definition of a keystone species. Theoretical and practical problems were found with the calculation of keystone status for different taxa. Given that important species cannot be shown to be keystones, and that calculation is technically difficult (and maybe impossible) the classification of seabirds, rats, or any other species as keystone is not likely to advance theoretical ecology or assist with conservation management. Attempts to define keystone species were found to be unsuccessful and abandonment of the term was advised.</p>

Ancient Invaders: How Paleogenetic Tools Help to Identify and Understand Biological Invasions of the Past

Past biological invasions have contributed to shaping our present day biodiversity. For many island ecosystems, they are the only source of terrestrial life. At the same time, biological invasions, in particular when caused by human activity, are a major concern for the conservation of native species. It is therefore essential to understand the drivers of biological invasions as well as the role invasions have played in different ecosystems. Molecular tools have provided valuable data to reconstruct biological invasions, their drivers, and their impacts. Recent technological developments have further increased the potential of molecular tools to track past shifts in biodiversity. Here, we provide a perspective on how such molecular tools have influenced our understanding of past biological invasions and discuss how they may further help to shape our understanding and management of biological invasions. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 52 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Phytolith and Calcitic Spherulite Indicators from Modern Reference Animal Dung from Mediterranean Island Ecosystems: Menorca, Balearic Islands

This study illustrates the contribution of plant and faecal microfossil records to interdisciplinary approaches on the identification, composition, taphonomy and seasonality of livestock dung materials. The focus is on the taphonomy of opal phytoliths and calcitic dung spherulites embedded within modern faecal pellets collected from pasture grounds and pens from a range of animals, including cattle, sheep and pigs from three different farms and seasons of the year in Menorca (Balearic Islands, Spain) declared a Biosphere Reserve by UNESCO. Modern reference materials provide comparative plant and dung microfossil indicators on factors affecting the formation, composition, preservation and decay of animal faeces, as well as on the diverse environmental and anthropogenic aspects influencing these. The reported results show relevant changes in phytolith and spherulite composition according to animal species and age, livestock management, seasonality, and grazing and foddering regimes. Both microfossil records provide fundamental information on taphonomic issues that are understudied, such as the variation in the digestibility among different species, including under investigated animals such as pigs, as well on the seasonality of plant and faecal microfossils that are excreted with dung as an important material for reconstructing human-environment interactions which is commonly overlooked in archaeology.