The long-term dynamics of invasive signal crayfish forcing of fluvial sediment supply via riverbank burrowing

Animals are important drivers of sediment dynamics. Invasive signal crayfish (Pacifastacus leniusculus) have been shown to supply sediment to rivers by burrowing into riverbanks. Burrowing directly transfers excavated sediment into the river and also has an additional indirect affect by promoting riverbank failure. While previous research has isolated burrow densities at a point in time, rates of burrow construction and of burrow loss due to erosion are unknown, which introduces uncertainty into estimates of how much sediment burrows contribute to rivers. Here we report results from a 5-year study that evaluated the temporal dynamics of crayfish populations, rates of burrow loss due to erosion, and the mass of sediment directly supplied to rivers by burrow excavation. At ten reaches across five lowland streams in England, we estimated the mass of sediment displaced by 1861 new and previously constructed burrows. Both crayfish and burrow densities were variable over time, suggesting that burrows contribute temporally variable amounts of fine sediment to riverine systems. 42 % of observed burrows were constructed within the previous 365 days, and individual burrows lasted on average 461 days. Applying this to comparable historical data, an average of 2.0 t km−1 a−1 of sediment was excavated to construct burrows in the study reaches, which is eight times more than estimated in previous studies. Whilst total burrow densities in each year were not consistently correlated with contemporary crayfish densities, the mass of sediment excavated over the prior year was strongly correlated with contemporary crayfish densities. Current fine sediment management practices are largely aimed at controlling fine sediment delivery, predominately from agricultural activities, but biotic burrowing into riverbanks may represent an important and overlooked source of fine sediment supply. Incorporation of biotic processes in sediment dynamics would improve the accuracy of fluvial sediment budgets and enhance the knowledge base underpinning effective fine-sediment management practices

Land use management in the Galapagos: A preliminary study on reducing the impacts of invasive plant species through sustainable agriculture and payment for ecosystem services

Terrestrial invasive species have been identified as one of the largest threats to endemic plants and wildlife in Galapagos, and their spread remains one of the biggest challenges for the region. The management of these species is a common link among all land‐use activities, and impacts all residents as economic activities in Galapagos are linked to its status as a unique landscape. The study aims, through the use of key informant interviews, policy documents and literature, to provide new insights into plant invasive species management by exploring two land‐use interventions—and the associated challenges and opportunities—currently being proposed by policymakers, academics, and other relevant actors. These are (a) local sustainable agricultural production and (b) policies and mechanisms, specifically the ‘Buen vivir’ paradigm with/and payments for ecosystem services. It explores how these can create bridges and be beneficial to both conservation and development. However, although the initiatives offer real opportunities to manage and control invasive species, challenges remain in the form of how these activities will be carried out and by whom. Findings show that probable success is dependent on community inclusion with coordinated and integrated approaches from robust institutions with connectivity among land‐use actors/managers. In addition, support is needed for organisations/stakeholders that are currently tackling the invasive species issue. Studies on land use remain crucial as relatively contained and pristine landscapes such as Galapagos are likely to be increasingly important as a means to detect human‐induced alterations at the frontiers of ecology

Integrating ecosystem services and disservices: insights from plant invasions

There is growing interest in ecosystem disservices, i.e. the negative effects of ecosystems on humans. The focus on disservices has been controversial because of the lack of clarity on how to disentangle ecosystem services and disservices related to human wellbeing. A perspective that considers both services and disservices is needed to inform objective decision-making. We propose a comprehensive typology of ecosystem disservices, and present a framework for integrating ecosystem services and disservices for human wellbeing linked to ecosystem functioning. Our treatment is underpinned by three key assumptions: (1) ecosystem attributes and functions are value-free; (2) the perception of benefits or nuisances are however dependent on societal context, and preferences and actions by societal actors may trigger, enhance or alleviate benefits or nuisances derived from ecosystems; and (3) the notion of disservices must account for the role of human management in assessments of ecosystem values, i.e. the social and technological measures that identify, protect, promote or restore desirable levels of services, and concurrently minimise, mitigate or adapt to disservices. We illustrate our ideas with examples from plant invasions as a complex social-ecological phenomenon

The long-term dynamics of invasive signal crayfish forcing of fluvial sediment supply via riverbank burrowing

Animals are important drivers of sediment dynamics. Invasive signal crayfish (Pacifastacus leniusculus) have been shown to supply sediment to rivers by burrowing into riverbanks. Burrowing directly transfers excavated sediment into the river and also has an additional indirect affect by promoting riverbank failure. While previous research has isolated burrow densities at a point in time, rates of burrow construction and of burrow loss due to erosion are unknown, which introduces uncertainty into estimates of how much sediment burrows contribute to rivers. Here we report results from a 5-year study that evaluated the temporal dynamics of crayfish populations, rates of burrow loss due to erosion, and the mass of sediment directly supplied to rivers by burrow excavation. At ten reaches across five lowland streams in England, we estimated the mass of sediment displaced by 1861 new and previously constructed burrows. Both crayfish and burrow densities were variable over time, suggesting that burrows contribute temporally variable amounts of fine sediment to riverine systems. 42 % of observed burrows were constructed within the previous 365 days, and individual burrows lasted on average 461 days. Applying this to comparable historical data, an average of 2.0 t km−1 a−1 of sediment was excavated to construct burrows in the study reaches, which is eight times more than estimated in previous studies. Whilst total burrow densities in each year were not consistently correlated with contemporary crayfish densities, the mass of sediment excavated over the prior year was strongly correlated with contemporary crayfish densities. Current fine sediment management practices are largely aimed at controlling fine sediment delivery, predominately from agricultural activities, but biotic burrowing into riverbanks may represent an important and overlooked source of fine sediment supply. Incorporation of biotic processes in sediment dynamics would improve the accuracy of fluvial sediment budgets and enhance the knowledge base underpinning effective fine-sediment management practices

Impacts of medusahead (Elymus caput-medusae L.) management on plant communities in California’s valley grasslands

California’s valley grasslands are one of the most invaded ecosystems in the state. It is estimated that valley grasslands contain between 90 to 99% cover of non-native plants. The most recent wave of invasive plants has included medusahead (Elymus caput-medusae L.). Medusahead is an annual grass that matures two to four weeks later than most other grasses. Management of medusahead includes the use of herbicides, targeted grazing, prescribed burns, and mechanical control. The primary focus of most studies on the use of these management methods is on the control of medusahead rather than the impacts on non-target plants. This study examines published research to determine what impact medusahead management has on the composition of plant communities within valley grasslands. Herbicides have mixed impacts on the percent cover of grasses and forbs. Targeted grazing resulted in decreased percent cover of non-native grasses and increased forb cover. Grazing results in neutral to increased percent cover of native plants. Prescribed burns decreased the percent cover of non-native grasses, increased forb cover, and had mixed impacts on native plant cover. Mechanical control shifted vegetative states towards forb or filaree (Erodium spp.) dominated communities. The non-target impacts of medusahead control were generally short-lived with differences in percent cover returning to baseline conditions within one to three years. To mitigate the non-target impacts of medusahead, revegetation efforts should be prioritized in sites with higher abundances of native plant species. The future success of controlling medusahead is dependent upon grassland restoration research, consistent funding for weed management areas to aid in managing invasive plants, and the implementation of monitoring after medusahead control treatments

The prioritisation of a short list of alien plants for risk analysis within the framework of the Regulation (EU) No. 1143/2014

Thirty-seven alien plant species, pre-identified by horizon scanning exercises were prioritised for pest risk analysis (PRA) using a modified version of the EPPO Prioritisation Process designed to be compliant with the EU Regulation 1143/2014. In Stage 1, species were categorised into one of four lists – a Residual List, EU List of Minor Concern, EU Observation List and the EU List of Invasive Alien Plants. Only those species included in the latter proceeded to the risk management stage where their priority for PRA was assessed. Due to medium or high spread potential coupled with high impacts twenty-two species were included in the EU List of Invasive Alien Plants and proceeded to Stage 2. Four species (Ambrosia trifida, Egeria densa, Fallopia baldschuanica and Oxalis pes-caprae) were assigned to the EU Observation List due to moderate or low impacts. Albizia lebbeck, Clematis terniflora, Euonymus japonicus, Lonicera morrowii, Prunus campanulata and Rubus rosifolius were assigned to the residual list due to a current lack of information on impacts. Similarly, Cornus sericea and Hydrilla verticillata were assigned to the Residual List due to unclear taxonomy and uncertainty in native status, respectively. Chromolaena odorata, Cryptostegia grandiflora and Sphagneticola trilobata were assigned to the Residual List as it is unlikely they will establish in the Union under current climatic conditions. In the risk management stage, Euonymus fortunei, Ligustrum sinense and Lonicera maackii were considered a low priority for PRA as they do not exhibit invasive tendencies despite being widely cultivated in the EU over several decades. Nineteen species were identified as having a high priority for a PRA (Acacia dealbata, Ambrosia confertiflora, Andropogon virginicus, Cardiospermum grandiflorum, Celastrus orbiculatus, Cinnamomum camphora, Cortaderia jubata, Ehrharta calycina, Gymnocoronis spilanthoides, Hakea sericea, Humulus scandens, Hygrophila polysperma, Lespedeza cuneata, Lygodium japonicum, Pennisetum setaceum, Prosopis juliflora, Sapium sebiferum, Pistia stratiotes and Salvinia molesta)

Urban plant invasions: how to classify, prioritize and manage invasive alien plants; Cape Town as a case study

Thesis (MSc)--Stellenbosch University, 2021.ENGLISH ABSTRACT: Urban areas are considered hotspots for invasions, with human activity being a major source of introduction and causing the dispersal of invasive alien plant species (IAPs). This makes natural and semi natural areas within and surrounding cities particularly susceptible to invasion. Cape Town is located within the Cape Floristic Region (CFR) which is considered a biodiversity hotspot; furthermore, this region has been identified as a UNESCO world heritage site. This biologically diverse area – which has some of the most recognizable and unique plant communities in the world – is therefore susceptible to invasion and is considered one of the most threatened biodiversity hotspots. IAPs pose a significant ecological and economic threat, impacting biodiversity and ecosystem services. Cape Town’s natural areas are also fragmented due to urbanization, where low lying areas are often developed and areas at higher altitudes are set aside for conservation purposes (such at the Table Mountain National Park). I reviewed the nature of urban invasions and the management strategies currently being employed to mitigate the impacts of IAPs within urban areas. I aimed to determine whether IAP richness and abundance is highest within natural areas within (or adjacent to) urban areas compared to peri-urban areas and rural areas and present management strategies to maintain ecological diversity throughout the city of Cape Town’s biological network of natural and semi-natural areas. I present a classification protocol developed from a literature review based on the feasibility of IAP eradication and grouped widespread IAPs, emerging IAPs and potential eradication targets into different management categories. In addition to this I adopted and tested a model for prioritization of emerging IAPs (known as early detection and rapid response [EDRR]) in the City of Cape Town (CCT) Metropolitan area. Finally, I focused on the emerging invader Hypericum canariense, and use lessons from earlier chapters to discuss feasibility of eradication of this species. I found that IAP species abundance was highest at the urban wildland interface (the peri-urban zone) between urban areas and rural areas. I discovered that disturbance in the natural and semi natural areas at the urban wildland interface plays a significant role in the invasion of IAPs into natural areas. In my classification protocol I identified that the area of infestation and the IAP species rate of spread are key indicators in classifying IAPs as widespread or emerging IAPs and for identifying potential eradication targets, noting that the three main management strategies for IAPS were mitigation, containment and eradication. Furthermore, the main criteria used in prioritizing emerging species in the Cape Town metropolitan area are “spread, negative impacts, ease of control and invasive potential”. I discovered that the emerging invader, H. canariense is feasible for eradication and that it would cost approximately ZAR57000 over a 10 year period to eradicate this species. I conclude that urban areas are important for effective IAP management and must not be disregarded or underestimate the role they play in the dissemination of IAPs into surrounding natural areas. The Peri-urban zone should be the focus of future management to ensure healthy biological networks. Conservationists and land managers should classify and prioritize species for management efforts instead of tackling species arbitrarily when funding is limited. Emerging species should be investigated in terms of their feasibility of eradication before undertaking potentially lengthy and costly eradication program.AFRIKAANSE OPSOMMING: Stedelike gebiede word beskou as brandpunte vir plant indringing met menslike aktiwiteite as oorsaak en bron van bekendstelling en verspreiding van uitheemse indringer plant spesies. (UIPS) Dit maak natuurlike en semi-natuurlike areas binne stede en hulle omliggende areas besonder vatbaar vir indringing. Kaapstad is gelee in die Kaapse Floristiese Ryk, wat beskou word as n biodiverse brandpunt; verder, dit is aangewys as n Unesco wereld erfenis gebied. Hierdie biologiese diverse gebied, met van die beduidendste en unieke plantgemeenskappe in die wereld, is vatbaar vir indringing en word beskou as een van die mees bedreigde biodiverse brandpunte. UIPS hou n beduidende ekonomiese en ekologiese bedreiging in met n gevolglike impak op biodiversiteit en ekosisteemdienste.. Kaapstad se natuurlike gebiede ook gefragmenteer as gevolg van verstedeliking, met laagliggende gebiede dikwels meer ontwikkel en hoerliggende areas tersyde gestel vir bewaringsdoeleindes (soos in die geval van die Tafelberg Nasionale Park). Ek het die aard van stedelike indringing nagegaan en die bestuurstrategieë t.o.v. die impak van UIPS tans in gebruik geëvalueer. My doel was om te bepaal of UIPS werklik meer oorvloedig voorkom in natuurlike gebiede wat grens aan stedelike gebiede en om bestuurstrategieë te ontwikkel om ekologiese diversiviteit in stand te hou in die biologiese netwerk van natuurlike en semi-natuurlike gebiede in die stasd Kaapstad. Hiermee bied ek n klassifikasie protokol aan wat ontwikkel is uit n literatuuroorsig en gebaseer op die moontlikheid om UIPS uit te wis en die wydverspreide UIPS te groepeer asook om nuwe (opkomende) UIPS en potensiële uitwissingsteikens in verskillende bestuurstrategieë te kategoriseer. Daarbenewens het ek n model vir die prioritisering van opkomende UIPS (vroee opsporing en spoedige reaksie strategie) vir die Metropolitaanse gebiede van Kaapstad aangeneem en getoets. Vir hierdie navorsing het ek gefokus op die opkomende indringer Hypericum canariense en gebruik gemaak van lesse geleer uit die voorafgaande hoofstukke om die moontlikheid van uitwissing van hierdie spesie te bespreek. Ek het bevind dat UIPS se voorkoms (volopheid) die hoogste was by die stedelike wildland-koppelvlak (peri-stedelike sone). Ek het vasgestel dat versteuring in die natuurlike en semi-natuurlike gebiede by die peri-stedelike sone n beduidende rol speel in die indringing van UIPS na natuurlike areas. (In my klassifikasie protokol demonstreer ek dat die gebied van besmetting en die tempovan die UIPS se indringing kritiese aanwysers is t.o.v. die klassifikasie van UIPS as opkomend of wydverspreid, en vir die identifisering van potensiële uitwissingsdoelwitte (daaroplettend dat die drie hoof bestuurstrategieë vir UIPS versagting, uitwissing en beperking is). Verder, die hoof kriteriums gebruik in die prioritisering van opkomende spesies in die Metropool van Kaapstad is verspreiding, negatiewe impak,hoe maklik beperking geïmplimenteer sal kan word en indringingspotensiaal. Ek het gevind dat die opkomende indringer, H. canariense, geskik is vir uitwissing en dat dit ongeveer ZAR 57000 oor n tien jaar periode sal kos om die spesie uit te wis. Ek het tot die gevolgtrekking gekom dat stedelike gebiede ‘n noodsaaklike rol speel in effektiewe UIPS beheer en nie onderskat moet word t.o.v. hulle aandeel in die verspreiding van UIPS na omliggende natuurlike gebiede nie. Die peri-stedelike sone behoort die fokus te wees vir effektiewe bestuurspraktyke om toekomstige gesonde biologiese netwerke te verseker. Natuurbewaarders en land bestuurders moet spesies klassifiseer en prioritiseer vir effektiewe bestuurstrategieë, eerder as om n spesies na willekeur aan te pak, terwyl fondse beperk is. Nuwe, opkomende spesies moet ondersoek en geëvalueer word t.o.v. die moontlikheid van hulle effektiewe uitwissing voordat potensiële duur en uitgerekte uitwissing programme geïmplimenteer word.Master

Trophic characteristics of aquatic habitats with different flooding regimes in the Okavango Delta, Botswana

In periodically flooded wetland systems, the seasonal flooding regime is the main driver of ecosystem functions. The relationship between a wetlands’ hydrology and ecosystem properties is therefore crucial to understand. Food web structure is an important ecosystem property that determines the stability of aquatic populations and hence the resilience of ecosystems to potential threats. While theoretical concepts predicting energy flow and food web dynamics in wetland ecosystems exist, there is still need for empirical research to validate the predictions to better inform local wetland management. My thesis examined the variability of algal primary productivity and, using stable isotope ratios of carbon and nitrogen (δ13C and δ15N respectively), the aquatic food web structure of differently flooded aquatic habitats within the Okavango Delta, in Botswana. The results from in-situ algal productivity incubations, showed that primary productivity rate is higher at Lake Ngami compared with Nxaraga lagoon and Phelo floodplain due to greater levels of dissolved nutrients at the lake. The relative importance of basal carbon sources for fish biomass production varied across study sites, but overall, algal sources were the principal basal carbon sources for fish across the study sites. The relative importance of carbon from macrophytes was greatest at Phelo floodplain during high flood. Based on Layman’s matrices of food web structure, fish from Lake Ngami had isotopically diverse carbon sources, greater food chain length and greater trophic niche diversity compared to fish from Nxaraga lagoon and Phelo floodplain. There was high degree of trophic niche overlap between different fish feeding guilds at all the study sites indicating opportunistic feeding behaviour among fish in the Delta. Together, the results demonstrate that the diversity of aquatic habitats within the Delta support different pathways of energy flow and different aquatic food web structures, which may be crucial for maintaining diverse ecosystem functions of the Delta

Spatiotemporal population genomics of marine species : invasion, expansion, and connectivity

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017Every genome tells a story. This dissertation contains four such stories, focused on shared themes of marine population dynamics and rapid change, with an emphasis on invasive marine species. Biological invasions are often characterized by a range expansion, during which strong genetic drift is hypothesized to result in decreased genetic diversity with increased distance from the center of the historic range, or the point of invasion. In this dissertation, population genetic and genomic tools are used to approach complex and previously intractable fundamental questions pertaining to the non-equilibrium dynamics of species invasions and rapid range expansions in two invasive marine species: the lionfish, Pterois volitans; and the shrimp, Palaemon macrodactylus. Using thousands of loci sequenced with restriction enzyme associated DNA sequencing in these two systems, this research tests theoretical predictions of the genomic signatures of range expansions. Additionally, the first chapter elucidates patterns of population genetic connectivity for deep-sea invertebrates in the New Zealand region demonstrating intimate relationships between genetics, oceanographic currents, and life history traits. Invasive shrimp results extend our understanding of marine population connectivity to suggest that human-mediated dispersal may be as important— if not more important—than oceanographic and life history considerations in determining genetic connectivity during specific phases of marine invasions. In invasive populations of lionfish, measures of genomic diversity, including a difference between observed and expected heterozygosity, were found to correlate with distance from the point of introduction, even in the absence of spatial metapopulation genetic structure. These results indicate a signal of rapid range expansion. The final study in this dissertation uses an innovative temporal approach to explore observed genomic patterns in the lionfish. In all, this dissertation provides a broad perspective through the study of multiple species undergoing superficially parallel processes that, under more intense scrutiny, are found to be mechanistically unique. It is only through comparative approaches that predictable patterns of population dynamics will emerge.I was privileged to receive support through a National Science Foundation (NSF) Graduate Research Fellowship (Grant No. 1122374), a Woods Hole Oceanographic Institution (WHOI) Fellowship administered through the Academic Program Office, funding from NSF award OCE-1131620, and the National Oceanic and Atmospheric Administration (NOAA OER #NA08OAR4600757). Research funding for sample collection, laboratory materials, sequencing, and analysis was provided by the WHOI Coastal Ocean Institute, WHOI Ocean Ventures Fund, WHOI James Education Fund for Ocean Exploration, WHOI Biology Educational Fund, Woods Hole Sea Grant New Initiative Award, Massachusetts Office of Coastal Zone Management, Northeast Sea Grant Consortium, and the PADI Foundation (Grant No. 14904). Additional research support was provided by the NSF (OCE- 1131620) to Timothy M. Shank