1,721,470 research outputs found
The effects of flooding disturbance on the distribution and behaviour of riparian arthropods along a lowland gravel river
Full text linkThis Ph.D.-thesis aimed to address which environmental factors influence the assemblage structure of mobile, riparian arthropods along spatially structured river banks of a rain-fed, lowland gravel river, the Common Meuse. As riverine ecosystems are basically non-equilibrium, dynamic ecosystems, mainly flow regimes and flood pulse characteristics are expected to shape both the distribution and behaviour of its inhabitants. The river banks along the Common Meuse are (in)frequently disturbed by flood events and liable to extreme microclimatological conditions. Hence, functional life-history traits of the present species, particularly spiders (Araneae) and carabid beetles (Carabidae), supposedly affect species composition as well. Moreover, organisms occurring within a highly structured system and which are repeatedly exposed to flooding disturbance, are expected to have evolved or adjusted their behavioural responses in accordance with their functional life-history characteristics such as habitat affinity and mobility. Correspondingly, less mobile species are expected to show variation in their spatial genetic structure as well.
Based on an intensive pitfall survey, increased anthropogenic alterations of water discharges were shown to cause the loss of stenotopic, xerothermophilic and less mobile riparian arthropods. Next to it, the results of two field experiments indicated that movement decisions of two sympatric wolf spiders (Lycosidae) were guided, particularly, by factors related to their population of origin (side of the river; either genetics or experience). A stenotopic riparian wolf spider, however, relied more on individual information (e.g. visual signals) and showed a higher degree of behavioural plasticity. This might increase the beneficiality of flood-avoiding behaviour. By using Amplified Fragment Length Polymorphism (AFLP) markers, the genetic population structure of the highly stenotopic wolf spider Pardosa agricola (Thorell, 1856) was studied. Nearby populations were less differentiated genetically than populations on different sides of the river, indicating the importance of functional connectivity along the riparian corridor.
River restoration and the rehabilitation of the riparian corridor should generate the required heterogeneity at the river bank level, hence increasing the sustainability of dynamic lowland river systems and realizing the conservation of vulnerable riparian arthropods. River management should consider the management of the alluvial hinterland as well to provide suitable refuges during flooding
Disentangling tree diversity, tree identity and edge effects : arthropod diversity and functioning
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Dune erosion during storm surges: The realdune/reflex experiment at the sand engine
No full textStorm conditions can lead to excessive dune erosion with potential floods as a consequence. Barrier islands and low-lying countries protected by dunes are especially vulnerable to dune erosion. To properly assess the risks these areas face, a clear understanding of the physical processes during dune erosion is required.An international field experiment was conducted to study dune erosion during storm surges from November 6 2021 until January 6 2022. on the Sand Engine. During the Realdune/Reflex experiment, two prototype un-vegetated dunes of 5.5 m high and 150 m long were built just above the high waterline. Due to a different shoreline orientation and nearshore bathymetry, these dunes eroded differently during moderate storm conditions. 3 storms were captured during the campaign.This abstract presents preliminary results of morphodynamic change during these 3 storms, by means of profile changes and erosion volumes.Coastal EngineeringEnvironmental Fluid Mechanic
The influence of dune pavilions on longer term dune development
No full textThe European beach-dune systems are under increasing pressure due to urbanization, beach tourism and the effects of climate change like rising sea level and increased storm intensity. Building with nature solutions (Stive et al., 2013) are advocated as an effective and adaptable approach to protect sandy coasts in the future. This approach however interacts with the increased human use of the beaches- which can have an adverse impact on the efficiency of the building with nature approach. Especially permanent structures influence the natural sand transport dynamics from the beach to the dunes and can have long lasting effects on dune development. To obtain more insight into the influence of buildings on longer term dune development a 3-months ‘Scanex 2020’ field campaign was conducted (Poppema et al., 2021) on Noordwijk beach (52.24 °N, 4.42 °E) to monitor the natural sand development around two sea containers (see Figure 1). In addition on a larger scale the dune development around a permanent beach pavilion was monitored for two years (from August 2019 till August 2021) within the CoastScan project (Vos et al., 2017) with a permanent laser scanner.Coastal EngineeringOptical and Laser Remote Sensin
Simulation of medium to long-term dune evoloution with interacting marine and aeolian sediment transport processes
No full textIn recent years, dune-in-front-of-dike projects have been carried out at several locations, e.g. at Raversijde and Oosteroever in Belgium and the Hondsbossche dunes in the Netherlands. In the near future, many coastal defence systems require reinforcement to adapt to rising sea levels, and often, natural values along the coasts may also be enhanced. Therefore, it is anticipated that this type of hybrid coastal protection – a mix of grey and green solutions – will become more common in the future. Contrary to grey defence structures, such as earth dikes and rock or concrete structures, dunes are dynamic features. Their level of flood protection depends on their morphological evolution due to aeolian and marine transport processes, vegetation dynamics, and anthropogenic impact. Numerical models are commonly used tools to assess the safety level of dunes and predict their future evolution. In addition to event timescales (storms), the decadal timescale is typically of interest from a coastal management perspective, especially when considering sea level rise. On this timescale, dune build-up through aeolian transport depends on the wind's transport capacity, and the availability of sediment of the appropriate size exposed to the wind is an important process. Sediment availability for aeolian transport is controlled by other sediment transport processes, such as dune erosion and longshore sediment transport, nourishments, and limiting factors, such as surface moisture and armour layers. Simulation of dune evolution at the decadal timescale requires an integrated model approach that accounts for the non-linear interactions between marine and aeolian transport processes in the longshore and cross-shore direction. Reduced complexity approaches are required when these models are applied to large temporal (decades) and spatial scales (kilometres). This study aims to predict medium to long-term dune evolution by developing a new coupled long- term beach and dune evolution model, coDaC (coupled Dunes and Coasts ). The new model combines a semi-empirical cross-shore transport model, the CS-model (Hallin et al. 2019a), with a longshore transport and coastline evolution model, Unibest CL+ (Figure 1). The coupled model is applied to simulate 22 years of morphological dune evolution along an 8 km-long coastal stretch at the Kennemer Dunes in the Netherlands.Coastal Engineerin
Evolutionaire ecologie van de gaffelwaterjuffer tijdens areaaluitbreiding
No full textRanges of manyspecies are shifting polewards in response to contemporary global warming. Rangeshifting species experience different selective forces at the expansion frontcompared with these experienced at the core of their range and this can havelarge impacts on the evolution of phenotypic traits at the expansion front.Determining changes in phenotypic traits during range expansion is important aschanges in traits may influence the rate of further range expansion, abioticinteractions and biotic interactions at the expansion front. Inthis thesis I combined field studies, indoor common garden experiments andoutdoor mesocosm experiments to obtain a multivariate picture on the traitdifferentiation and associated changes in (a)biotic interactions during thepoleward range expansion of the damselfly Coenagrionscitulum. Phenotypicdifferentiation associated with northward range expansion Two importantaspects may induce evolution in phenotypic traits during range expansion.Firstly, populations at the expansion front are assorted by dispersal ability,whereby only the best dispersers colonize the expansion front. Secondly,population densities in newly founded populations at the expansion front arelow which may change selection regimes for life-history traits. Besides effectsof the range expansion process per se, also geographically structured thermalregimes may contribute to changes in phenotypic traits during range expansion.Geographicallystructured thermal regimes in both the larval (length of the growth season) andadult stage (adult flight period temperature) had an impact on different traitsinvestigated. Yet, importantly, these temperature regimes had only a smallcontribution to the phenotypic differentiation between core and edgepopulations. I documented in different studies changes in flight-related traitsthat indicate a better flight ability at the expansion front. I found higherinvestment in flight muscle mass, a lower wing loading and a larger relativethorax length at the range expansion front of C. scitulum. Higher flight ability at the expansion front mayevolve through natural selection whereby individuals that disperse most rapidlyat the expansion front benefit from the low densities of conspecifics at therange edge, and through spatial sorting in dispersal ability. Linked to theevolution of higher dispersal ability, adults at the expansion front had ahigher immune response (encapsulation response). Selection for a highinvestment in immune function to lower parasite load may occur through anegative effect of high parasite load on dispersal ability. Theory predictsselection for a higher population growth rate at the expansion front, which isfavoured at the low population densities in newly colonized habitats. At theexpansion front of C. scitulum Idocumented faster larval growth and development, while fecundity did not differbetween core and edge females. I documented for the first time, an increase ofactivity level in the non-dispersive larval stage at the expansion front; whileno higher activity in adults at the expansion front was detected. My resultsindicated that the higher larval activity at the expansion front evolved tomeet a higher energy demand in edge populations that is allocated to fastergrowth and higher investment in flight-related traits at the expansion front. Abiotic andbiotic interactions at the expansion frontLow foodconditions and high competition had a negative effect on growth rate of larvae;additionally low food conditions in the larval stage decreased investment inflight muscle mass hence likely dispersal ability. Furthermore, my results suggesta higher susceptibility of edge larvae to food limitation, which highlights theimportance of optimal local conditions at the expansion front for animalfitness and further range expansion. In contrast, winter survival was nothigher in edge larvae, indicating that no thermal adaptation for enhancedwinter survival at the expansion front occurred.Thehigher investment in dispersal, faster life history and higher larval activitywas expected to influence biotic interactions at the expansion front. Higherlarval activity and growth at the expansion front may increase visibility tovisual predators, hence was expected to increase predation risk by Anax imperator larvae. Furthermore,given that higher activity and growth rates typically are associated with abetter competitive ability, we predicted larvae at the expansion front to besuperior competitors relative to larvae from core populations. In contrast tothese expectations, we did not find a difference in predator-prey interactionsnor larval competitive ability between core and edge larvae. The relativelysmall changes in larval growth and activity during the range expansion of C. scitulum may be too small to have aprofound impact on the studied biotic interactions. Sexual selection for higherflight duration of males was consistent in core and edge populations. Incontrast, I detected geographical patterns in sexual selection for male bodysize and fat content, however these geographical patterns were rather shaped bydifferences in thermal regimes than by processes associated with rangeexpansion per se.My study not only adds to thegrowing number of studies that document rapid evolutionary changes in dispersaland life-history during range expansion, but also contributes to the scarcestudies investigating abiotic and biotic interactions at the expansion front.Furthermore, my study is the first to document the evolution of a higher adultimmune response and a higher activity level in the non-dispersive larval stageat the expansion front, which may give rise to eco-evolutionary dynamics. 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Far-reaching effects of root herbivory on pollinator-interactions and plant performance in Cynoglossum officinale
Full text linkEco-evolutionary dynamics during range expansion in a herbivorous arthropod
Full text linkThe earth’s climate has a history of alternating glacial and interglacial periods, which have recurrently forced major rearrangements in species assemblages. Today, however, scientists are worried because the predicted rate of climate change is faster than any of these past temperature changes, and anticipated to have dramatic consequences for the earth’s biodiversity. One way in which species may respond to the current global warming, is by shifting their range pole- or upwards. During such shifts, individuals encounter changing environmental conditions (like a shortened breeding season) and become assorted according to their dispersal capacities (best dispersers at the front). Range shifts thus entail strong selection pressures that may profoundly shape range front phenotypes. This PhD thesis studies the ecological and evolutionary processes related to range shifts, using the two-spotted spider mite (a herbivorous pest that recently expanded its European range northwards) as a model species
Integrating metabolic theory and movement ecology to understand metapopulation and -community dynamics
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