Invasive species

Abstract
Invasive species are a worldwide threat to biodiversity, especially on Caribbean islands.
Through their impact on the structure and functioning of ecosystems, they also affect
ecosystem services. Therefore, invasive species can have profound socio-economic
effects. On the Dutch Caribbean Island of St. Eustatius, the invasive perennial vine Coralita
is present on roughly 33% of the Island. While ecological damage is evident, effective
management strategies are still lacking. This study links the ecological, cultural and
societal effects of the invasion to the economy of the Island by estimating the ecosystem
service losses due to Coralita in monetary value. We have spatially assessed the
economic value of five main ecosystem services (tourism, non-use value, carbon
sequestration, archaeology and local cultural and recreational value) to the different
habitats on the Island and estimated the loss of these values under three scenarios of
Coralita cover: 0%, 3% and 36% dominant cover. The baseline scenario of 0%
demonstrated a total ecosystem service value of $2.7 million per year, concentrated on the Quill volcano. The 3% and 36% scenario showed a yearly loss of $39,804 and $576,704, respectively, with the largest losses located on the northern and eastern slopes of the Quill.
These areas should be prioritised for management and the known potential gain per area
enables choice of strategy, based on cost-benefit considerations. To reduce further
economic loss by Coralita, we urgently advise an immediate management strategy and
ongoing research into eradication and restoration methods.

Keywords
BES Islands, Coralita, economic value, invasive species, spatial assessment, scenario
mapping

Abstract

Hemidactylus mabouia is one of the most successful, widespread invasive reptile species and has become ubiquitous across tropical urban settings in the Western Hemisphere. Its ability to thrive in close proximity to humans has been linked to the rapid disap-pearance of native geckos. However, aspects of Hemidactylus mabouia natural history and ecomorphology, often assumed to be linked with this effect on native popula-tions, remain understudied or untested. Here, we combine data from ∂15N and ∂13C stable isotopes, stomach contents, and morphometric analyses of traits associated with feeding and locomotion to test alternate hypotheses of displacement between H. mabouia and a native gecko, Phyllodactylus martini, on the island of Curaçao. We demonstrate substantial overlap of invertebrate prey resources between the species, with H. mabouia stomachs containing larger arthropod prey as well as vertebrate prey. We additionally show that H. mabouia possesses several morphological advantages, including larger sizes in feeding-associated traits and limb proportions that could offer a propulsive locomotor advantage on vertical surfaces. Together, these findings pro-vide the first support for the hypotheses that invasive H. mabouia and native P. martinioverlap in prey resources and that H. mabouia possess ecomorphological advantages over P. martini. This work provides critical context for follow-up studies of H. mabouiaand P. martini natural history and direct behavioral experiments that may ultimately il-luminate the mechanisms underlying displacement on this island and act as a potential model for other systems with Hemidactylus mabouia invasions.

KEYWORDSfood web, invasive species, trophic ecology, urbanization, vertebrate biodiversity loss
 

Student Report

After six months of ethnographic fieldwork on Saba, a small island in the Caribbean Netherlands, the student developed her thesis drawing together dynamics of sovereignty, development, and invasive species control to understand the environmental challenges facing the island today. The researcher used a combination of participant observation, unstructured interviews, and collected life-stories to understand the ways environmental conditions shape human, plant, and animal life on Saba. In understanding these dynamics, the researcher was able to draw conclusions about ecotourism development and invasive species control that inform current methods of environmental conservation throughout the Caribbean.

On the Caribbean island of St. Eustatius, Coralita (Antigonon leptopus) is an aggressive invasive vine posing major biodiversity conservation concerns. The generation of distribution maps can address these conservation concerns by helping to elucidate the drivers of invasion. We test the use of support vector machines to map the distribution of Coralita on St. Eustatius at high spatial resolution and use this map to identify potential landscape and geomorphological factors associated with Coralita presence. This latter step was performed by comparing the actual distribution of Coralita patches to a random distribution of patches. To train the support vector machine algorithm, we used three vegetation indices and seven texture metrics derived from a 2014 WorldView-2 image. The resulting map shows that Coralita covered 3.18% of the island in 2014, corresponding to an area of 64 ha. The mapped distribution was highly accurate, with 93.2% overall accuracy (Coralita class producer's accuracy: 76.4%, user's accuracy: 86.2%). Using this classification map, we found that Coralita is not randomly distributed across the landscape, occurring significantly closer to roads and drainage channels, in areas with higher accumulated moisture, and on flatter slopes. Coralita was found more often than expected in grasslands, disturbed forest, and urban areas but was relatively rare in natural forest. These results highlight the ability of high spatial resolution data from sensors such as WorldView-2 to produce accurate invasive species, providing valuable information for predicting current and future spread risks and for early detection and removal plans.

Referenced in BioNews publication (BioNews Article). 

Related Resources:

1. Supplementary Infromation (Report)

2. Topographic Wetness Index raster layer for Statia developed for use in the Coralita mapping publication (Raster Layers). 

3. Raster layers: High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopus on St. Eustatius (Lesser Antilles) (Raster Layers).

The native herpetofauna of the Lesser Antillean island of Saba (13 km2; 17.63°N, -63.24°W) includes one snake, Alsophis rufiventris, and four species of lizards, Anolis sabanus, Iguana melanoderma, Sphaerodactylus sabanus, and Thecadatylus rapicauda (Powell et al. 2015). Here, we report the establishment of both Gymnophthalmus underwoo-di Grant, 1958 and Indotyphlops braminus (Daudin, 1803) on the island.

This one-year pilot project aims to provide an insight in the ecology of Antigonon leptopus (Corallita) an invasive vine, which is overgrowing the native vegetation (Photo 1). This pilot project is just a first step in controlling the Antigonon leptopus. This research was done on a small scale and under controlled circumstances. Our ideas are just for small scale use in town but also to eradicate ‘hotspots’ to prevent further spreading especially near the National Parks. The government with STENAPA as a consultant should take further actions to continue this project and put it as a high priority. The first step was made and we hope this will contribute in containing the species and monitoring the species closely. More research on the life circle and possible natural enemies and its sensitivity for herbicides should be done in order to start a larger scale eradication campaign. The project does not stand on its own, the vine contributes in the prevention of soil erosion on the island. A full size project including replanting/reforestation with native species and renewed agricultural activities should be set up for the long term.

Objectives

• The primary research aim is to reduce and control the growth of Corallita on St. Eustatius and to prevent the species from invading the national parks. In order to achieve this, it is necessary.
• To gather information about the ecology of the species, such as its life cycle, dispersal, germination capacity, use of the species by animals etc. • To gather information about how the species will react on different potential control methods.
• Inform the local community about control methods if usable results are obtained.

Discussion and conclusion

Three weeks after the first treatment at Gallow Bay no regrowth was observed, this means the herbicide does work with smaller concentration (12.5% and 25%) on short term. After six weeks the first regrowth was observed. The tubers are still intact after the first treatment. It is not known how many times the treatment with these concentrations is needed.

In both plots of Sandy Road the plants have regrowth after 7½ weeks. Our observation on 13th January 2007 showed that a lot of Corallita was growing from the border into the plots covering the soil. The treatment did work but probably needed a second treatment if there is regrowth of 30-40cm. Further monitoring of large plots (during one year) is needed to make sure smaller concentrations will kill the plants. Tubers should de dug up and checked on viability. New plots should be selected.

ABSTRACT: Juvenile queen conch are primarily associated with native seagrass such as Thalassia
testudinum in large parts of their range in the Caribbean and the southern Gulf of Mexico. Here,
a number of non-native seagrass species have been introduced including Halophila stipulacea,
which is natural to the Red Sea and the Indo-Pacific. In the Caribbean, H. stipulacea often creates
dense continuous mats with little or no sediment exposed, compared to native seagrass, which
grows much less dense. We examined the diet and growth of juvenile conch in both native, mixed,
and invasive seagrass beds using stable isotope analysis and an in situ growth enclosure experiment.
Organic material in the sediment (i.e. benthic diatoms and particulate organic matter) was
found to be the most important source of carbon and nitrogen for juvenile queen conch in all 3
habitats investigated, and there was a significantly higher probability of positive growth in the
native seagrass compared to the invasive seagrass. Due to the importance of the organic material
in the sediment as a source of nutrition for juvenile conch, limited access to the sediment in the
invasive seagrass can potentially cause inadequate nutritional conditions to sustain high growth
rates. Thus, it is likely that there is a negative effect on juvenile queen conch growth currently
inhabiting invasive seagrass beds, compared to native seagrass beds, when other potential
sources of nutrition are not available.

Since the furry stowaways landed here aboard sealing and whaling ships in the 19th century, they've been wreaking ecological havoc on the island and its ground-nesting seabirds by preying on the birds and their eggs.

Enter an international team of wildlife biologists, who have recently completed the second phase of history's largest rat-eradication program on the remote island.

Braving appalling weather in the run-up to the Antarctic winter, the group's helicopter pilots logged hundreds of hours in perilous flying conditions to spread nearly 200 tons of rat poison over 224 square miles (580 square kilometers) of South Georgia's coastline.

The ultimate goal: To rid this once supreme seabird habitat of its millions of rats once and for all. South Georgia was probably the richest seabird-breeding area in the world when British Captain James Cook visited it in 1775, according to Tony Martin of the University of Dundee, who leads the rat-eradication campaign on behalf of the South Georgia Heritage Trust. (See more pictures of South Georgia.)

Now the island has less than one percent of its original seabird population, he said. "And that is down to rats. This is a human-induced problem, and it is down to humans to do something about it."

And they are. This recent bait drop follows a successful trial two years ago, which cleared 10 percent of South Georgia of the invasive rodents. Next year, Martin said, the group plans to return and finish the job, hopefully rendering South Georgia rat-free by 2015.

Sint Eustatius:---The island of Sint Eustatius has initiated an ambitious two-year project to reduce the number of rats on the island. The project has two leaders, Hannah Madden (Caribbean Netherlands Science Institute), who will look into the impact of rats on biodiversity, and Dr. Teresa Leslie (Eastern Caribbean Public Health Foundation), who will investigate the public health threat. Through these combined activities it is the responsibility of these co-investigators to significantly decrease the number of rats on the island and implement a sustainable rat control program.

Rats in Sint Eustatius are increasingly becoming a problem to humans and nature alike. According to Madden, “rats eat almost everything, from flowers and fruits to plants and meat. Not just agricultural produce, but also the native flora and fauna of the island, are impacted. This could very well result in a reduction of the number of different plants and animals found on Statia, which has happened on rat-infested islands elsewhere. A decline in the island’s biodiversity has various negative effects. It affects ecosystem products and services (such as fresh water and food), and indirectly affects livelihoods and income.” She continues by stating how “rats have been documented eating the single-egg clutch of red-billed tropicbirds during the nesting season, and are likely to impact many other vertebrate species on Statia.”

According to Leslie, in addition to being a risk to nature and biodiversity, rats pose a major threat to public health. Rats carry potential diseases which pose a direct risk to human and animal health”. “The bacterial disease leptospirosis, which is often associated with rats, poses a serious threat in the Caribbean and is not adequately documented” says Leslie. Through a collaboration with Ross University School of Veterinarian Medicine in St. Kitts, a component of this work will investigate diseases rats in Statia may be carrying. Leslie believes that “knowing about potential diseases can be used to raise community awareness about the need to reduce the number of rats on the island”.

Both Madden and Leslie agree that community involvement is critical to the success of the program. ”The people of St. Eustatius identify rats as an island problem. However, there is no systematic approach to their control” says Leslie. According to Madden, “in order for this project to be successful, the community must be engaged and understand that they can play a major role in solving our rat problem”.

This two-year, island-wide rodent control project began on February 1. The project is funded by the Netherlands Ministry of Economic Affairs and facilitated through the Caribbean Netherlands Science Institute (CNSI). In 2019, the Public Health Department will continue to implement the rodent control program created by Leslie and Madden to ensure long-term sustainability.

Abstract: Invasive rats are some of the largest contributors to seabird extinction and endangerment world- wide. We conducted a meta-analysis of studies on seabird–rat interactions to examine which seabird phyloge- netic, morphological, behavioral, and life history characteristics affect their susceptibility to invasive rats and to identify which rat species have had the largest impact on seabird mortality. We examined 94 manuscripts that demonstrated rat effects on seabirds. All studies combined resulted in 115 independent rat–seabird in- teractions on 61 islands or island chains with 75 species of seabirds in 10 families affected. Seabirds in the family Hydrobatidae and other small, burrow-nesting seabirds were most affected by invasive rats. Laridae and other large, ground-nesting seabirds were the least vulnerable to rats. Of the 3 species of invasive rats, Rattus rattus had the largest mean impact on seabirds followed by R. norvegicus and R. exulans; nevertheless, these differences were not statistically significant. Our findings should help managers and conservation prac- titioners prioritize selection of islands for rat eradication based on seabird life history traits, develop testable hypotheses for seabird response to rat eradication, provide justification for rat eradication campaigns, and identify suitable levels of response and prevention measures to rat invasion. Assessment of the effects of rats on seabirds can be improved by data derived from additional experimental studies, with emphasis on understudied seabird families such as Sulidae, Phalacrocoracidae, Spheniscidae, Fregatidae, Pelecanoididae, Phaethontidae, and Diomedeidae and evaluation of rat impacts in tropical regions.