Studying human-nature interactions requires an inter- and trans-disciplinary perspective, and highlights the need for a systematic and structured integration of social science approaches in conservation science and action.

This presentation will showcase highlights from recent projects I led at the Open University of the Netherlands, at Hasselt University and at the VUB & ULB universities of Brussels, Belgium. As an Assistant Professor in Environmental Governance, and as a Visiting Professor in Biology, I have a specific interest in collaborative environmental governance, social-ecological systems management, biodiversity conservation effectiveness, ecosystem services, the plural valuation of nature and human-wildlife conflicts.

Together with my colleagues, I have worked on a range of international research projects, often focusing on mangroves as model systems. Although mangroves are increasingly recognized for the many benefits they provide to humans, they are under threat due to heavy development pressures along tropical coastlines. Understanding and integrating the perspectives of a range of mangrove management stakeholders is key for sustainable mangrove conservation – and this requires the development and application of a range of –social- science methods. Next to mangroves and other coastal systems, our research also focuses on the effectiveness of protected areas (PAs) and on conservation conflict mapping and mitigation.

I will also zoom in on two international Master programmes I’m teaching in: the Tropimundo Master on Tropical Ecosystems and Biodiversity and the Master in Marine & Lacustrine Science & Management (Oceans & Lakes) and briefly introduce our field school experience in mangrove settings. The whole idea is to explore common interests and to reflect on collaboration opportunities.

Sex-biased predation occurs when one sex of a prey species is consumed more than the other, irrespective of their relative availability (sex-ratio). Some of the potential factors leading to sex-biased predation are sex differences in morphology and/or behaviour of prey species. In the context of mate-finding, we often see sex-specific behavioural strategies, such as signalling and searching. The relative risk of predation on the two sexes during mate-finding depends on who signals, who searches, the risks associated with these behaviours, and the degree of involvement in these activities. Prey wing remains found in the roosts of a bat predator, Megaderma spasma, reveal interesting patterns for two katydid genera, Mecopoda and Onomarchus. Mecopoda sp. wing remains are male-biased in the breeding season and female-biased in the non-breeding season, while Onomarchus uninotatus wing remains are female-biased year-round. These two katydids differ in their mate-finding strategies: in Mecopoda sp., which are found close to the ground, males signal acoustically and females search silently to locate them. Onomarchus uninotatus is an arboreal katydid, that uses an acoustic-vibratory multimodal duet for mate-finding within trees, with both sexes signalling and searching to find mates.

To explore the factors driving the sex-biased predation by M. spasma on Mecopoda sp., I used a combination of field observations and enclosure experiments with wild-caught live animals. The males and females of Mecopoda sp. were compared with respect to (i) their availability, i.e., natural sex-ratio across the seasons, (ii) the predation risks associated with different behaviours, and (iii) the prevalence of their risky behaviours in the wild. The results show that the relative availability of the sexes does not explain the male-biased predation on Mecopoda in the breeding season; whereas in the non-breeding season, very few males are available, which could lead to the female-biased predation. Males perform high-risk mate-finding behaviours, such as calling and flight, with a high prevalence in the wild. Although flight is equally risky for both sexes, females rarely fly.

To understand bat predation risk on male and female O. uninotatus and its possible role as a selection pressure driving the evolution of multimodal duetting, outdoor enclosure experiments were performed with live bats and katydids. Bat predation risks were compared (i) between the signalling and searching strategies of each sex, and (ii) between male and female signalling. The findings indicate that bat predation risk fails to explain the evolution of vibrational signalling in O. uninotatus females, as searching by walking is as safe as signalling, leading to an overall low predation risk on females within a tree. However, their duetting behaviour lowers the risk on males, who can shift from high-risk signalling to low-risk searching by walking, once females start signalling.

Finally, I focused on bat predation risk of searching behaviour in O. uninotatus, which potentially takes flights across trees. Comparisons were made between males and females for (i) bat predation risk of flight using enclosure experiments and (ii) across-tree movement patterns using radio-telemetry. I found that flight is equally risky for both sexes, but females move across trees 1.6 times more often and 1.8 times greater distances, which could make them more vulnerable to predation, offering a possible explanation for the female-biased prey remains found in M. spasma roosts.

Overall, this thesis provides a comprehensive examination of the predation risks associated with signalling and searching behaviours of katydids. The interplay between sex-specific behaviours and ecological factors can explain sex-biased predation patterns.

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The terrestrial carbon (C) cycle involves fluxes between multiple pools that determine ecosystem functions and regulate global climate. These fluxes and pools are influenced by changes in abiotic (temperature, precipitation etc.) and biotic (animals, microbes, etc.) factors. In this thesis, I address three questions on how these abiotic and biotic drivers influence the size and stability of these fluxes and pools. In the first chapter, I investigate how covariation between decadal trends (2001-2019) in temperature and precipitation influence the two opposing C-fluxes in the soil-C pool – (1) C-influx through primary production (NPP), and (2) C-efflux through soil heterotrophic respiration (Rh). I estimate how any imbalance between these opposing fluxes affects the vulnerability of soil-C across the globe. I find that changes in C-influx may not compensate for rising C-efflux, under wetter and warmer conditions. Soil-C loss can occur in both tropics and at high latitudes, and precipitation emerged as the key determinant of soil-C vulnerability in a warmer world. This implies that hotspots for soil-C loss/gain can shift in the coming decades to make the soil-C pool vulnerable to climate change despite widespread increase in NPP across the world. In the second chapter, I explored the influence of climate on long-term correlations in vegetation fluctuations (i.e., persistence, measured by the Hurst exponent from time-series data). I found evidence for stronger persistence in warm and dry regions of the world, and there were non-linear relationships between persistence and two key climate variables (i.e., temperature and precipitation). While average temperature and precipitation together explained nearly three-fourths of the spatial variation in vegetation persistence, they had limited ability to explain the observed temporal changes in persistence. We find evidence for change in vegetation persistence across the globe driven by background change in climate. This provides some new insights into the resistance/resilience of vegetation in different ecosystems.  In the third chapter, I investigated how animals – large mammalian herbivores – influence the terrestrial carbon cycle. Their influence on the size of the soil-C pool is well known, but how herbivores control the temporal stability of soil-C has remained largely unknown. I used a long-term field experiment in the Trans-Himalaya (2005-present) to estimate the consequences of herbivore-exclusion on interannual fluctuations in soil-C. I found high interannual variability in soil-C, and herbivores promote temporal stability of soil-C. Grazing by herbivores also mediated the influence of nitrogen on the stability on soil-C. Therefore, conserving large mammalian herbivores in grazing ecosystems can help achieve nature-based climate solutions. Overall, this thesis explores the linkages between three aspects of the terrestrial carbon cycle and climate, and herbivores. It highlights the non-linearities in vegetation-soil-animal interactions which are important for the stability of the terrestrial carbon cycle. 

Parasites and pathogens are ubiquitous in that they affect almost any aspect of life. They influence host populations and entire communities, but can also target specific groups of hosts. A fundamental challenge of infectious disease epidemiology and evolutionary ecology is to identify the factors contributing to the emergence of epidemics and the spread of diseases, and to assess their epidemiological, ecological and evolutionary consequences. An important yet often overlooked factor influencing variation in disease susceptibility and disease spread is the age of the host. Whereas phenomena relating host age to infectious disease biology of humans and other vertebrates are well known, little is known about age effects in invertebrates and they are hardly taken into consideration in studies of host-parasite interactions and evolutionary ecology. This stands in contrast with the role of invertebrates in human well-fare (invertebrates are often vectors for human diseases) as well as their contribution to apiculture and aquaculture, the maintenance of biodiversity and ecosystem functioning. Previously I found that host age at exposure directly affects the interactions between the bacterium Pasteuria ramosa and its water flea host Daphnia magna. Here, I will show that similar age effects are present in single and multi-strain infections by the microsporidian Hamiltosporidium tvaerminnensis, a mixed-mode parasite of D. magna. Using three species of Daphnia (two clones from each host species), and two isolates of the pathogenic yeast Metschnikowia bicuspidata, I will also show the generality and diversity of host age effects. I will further show that clearance of P. ramosa in 30-day-old D. magna can occur at progressed infection phases, a rarely documented phenomenon in invertebrates. Finally, I will show how experimental evolution can be used to test if the parasite can adapt to the host age class it infects predominantly. Ultimately, elucidating the underlying dynamics will improve our understanding of disease ecology and virulence evolution.

 Small isolated populations are the history of living beings. Studies of demographic histories of non-model organisms reveal that almost all populations have faced severe bottlenecks at least once in the past. Additionally, speciation events are often correlated with founding bottlenecks. Classical population genetics theory suggests small isolated populations are faced with threats of extinction. This is generally visualized as an extinction vortex where, small populations lose diversity due to stochasticity and inbreeding leading to reduced fitness of the individuals accompanied with reduced survival and fewer offspring further leading to a smaller population spiralling to extinction. However, despite the severe bottlenecks faced we observe the present biodiversity. Genomics studies of wild populations threatened with extinction present insights into how populations may have persisted over time to escape the extinction vortex. Modern insights from studies of threatened populations highlight the importance of neutral genetic diversity along with the role of purging and geneflow in the persistence of populations. Here, using tigers, rhinocerous and elephant populations, I illuminate a potential model of survival and extinction in small populations that might explain the observed biodiversity. Additionally, I will explore some ways in which research on small populations can be promoted in the tropical countries generally underrepresented in the literature.

Mangrove forests inhabit the intertidal areas along the tropical and subtropical coastal regions and monitor the exchange of matter at the edges of terrestrial, marine and atmospheric ecosystem. This specialized ecosystem offers several ecosystem services, like alleviating coastal erosion by wind and waves, ensuring fishery resources and food security for coastal population, and protecting the coastal biodiversity. It plays a key role in carbon exchange cycle and is an important blue carbon sink that can aid in the mitigation of climate change. However, mangroves are highly vulnerable to climate change and fluctuations in relative sea level. The mangroves are harmed by low intensity precipitation due to less freshwater discharge, fluvial silt, and nutrient input into the mangrove habitats. High frequency winter cooling episodes can also hinder mangrove development due to variations in monsoon intensity. Hypersaline environments with high evaporation rates brought on by extreme warming episodes also cause mangrove forest degradation. Moreover, anthropogenic pressures, such as overexploitation of resources, environmental pollution, and landuse/landcover changes, have greatly impacted the mangrove ecosystem. Currently, the world is seeing rapid sea level rise, frequent extreme climatic events, and an ever-rising population. Hence, the reconstruction of past mangrove responses through climate indicators recorded in sediments provides a baseline data for species distribution models in predicting the fate of mangrove ecosystem under the influence of rapid environmental changes.

Fossil pollen plays a vital role as a direct proxy for estimating vegetation cover in the past and an indirect proxy for understanding past climate. Palynological assemblages from estuarine formations are constantly influenced by both marine and terrestrial factors such as coastal erosion, accretion by rivers or sea, tidal waves, high salinity, water-logged soils and other edaphic factors due to their location along coasts. This, along with the distance from shoreline, duration and frequency of tidal inundation govern the distribution of mangrove species and their succession. Hence, studies attempting to identify the modern pollen dispersion and deposition processes, test correlations between pollen, vegetation, and climate using models, and compare these models with fossil pollen databases for reconstructing the key plant species distribution at a continental spatial scale are much needed for climate modelling studies.

Conservation is fundamentally about human behavior. Protecting biodiversity and mitigating climate change requires that stakeholders across different sectors and societies cooperate and act. My work has used data science techniques ranging from the local scale, focused on interviewing resource users in tropical Asia, to the global scale of social media to elucidate the social, economic, and ecological factors that shape human interactions with nature. I will discuss several case studies that highlight how text analyses and online “Big Data” can generate powerful new insights for conservation and social-ecological systems research. I will discuss work that performs a systematic characterization of environmental personas on social media, using natural language processing to geolocate users and evaluate their views toward the environment. I will discuss how these findings can drive new approaches for conservation messaging and engagement. Finally, I will show how large language models can be used to synthesize and map evidence for natural climate solutions at a global scale.

Plant domestication, a process spanning about 10,000 years, involves the selective nurturing of wild species to meet human needs, leading to the domesticated crops we see today. Papaver somniferum, cultivated for food, ornamental, and medicinal purposes, serves as an ideal model to study trait changes under domestication. The first chapter of my thesis will compare morphological, phenological, and phytochemical traits across Papaveraceae varieties, focusing on P. somniferum domesticated for specific purposes versus related taxa unaffected by human intervention. This chapter will explore "domestication syndromes" (DS), such as changes in defensive chemicals, seed morphology, and biochemistry, to understand how these traits vary with different domestication goals. This analysis will use plant trait measurements taken from existing literature and from plants grown in a controlled environment.

The second chapter examines how plant traits associated with domestication in P. somniferum vary with the intensity of management and contrasting biogeographical contexts: Plains, Plateaus, and Mountains. Mountainous regions, with low human intervention, contrast with the more intensively managed farmlands of plateaus and plains. I expect to find that differences in human management practices, influenced by the constraints and opportunities of each landscape, along with cultural differences between farming communities affect the domestication intensity of this species. For this, I will use field observations, questionnaires, and surveys to identify practices impacting artificial selection in plants.

In the third chapter, I investigate how seed trade and spatial connectivity affect the spatial genetic population structure of P. Somniferum. By comparing poppies from fields in the highly connected Gangetic plains, moderately connected Marwar plateau, and the least connected Mishmi hills – using microsatellite-neutral markers – the aim is to reveal how landscape connectivity and human-mediated gene flow through seed trades and cultural connectivity shape the genetic diversity and structure of these geographically varied subpopulations.

Once every 13 or 17 years within eastern North American deciduous forests, billions of periodical cicadas concurrently emerge from the soil and briefly satiate a diverse array of naive consumers, offering a rare opportunity to assess the cascading impacts of an ecosystem-wide resource pulse on a complex food web. We quantified the effects of the 2021 Brood X emergence and report that more than 80 bird species opportunistically switched their foraging to include cicadas, releasing herbivorous insects from predation and essentially doubling both caterpillar densities and accumulated herbivory levels on host oak trees. These short-lived but massive emergence events help us to understand how resource pulses can rewire interaction webs and disrupt energy flows in ecosystems, with potentially long-lasting effects. (And India has the world’s only other reported species of periodical cicadas!)

Once every 13 or 17 years within eastern North American deciduous forests, billions of periodical cicadas concurrently emerge from the soil and briefly satiate a diverse array of naive consumers, offering a rare opportunity to assess the cascading impacts of an ecosystem-wide resource pulse on a complex food web. We quantified the effects of the 2021 Brood X emergence and report that more than 80 bird species opportunistically switched their foraging to include cicadas, releasing herbivorous insects from predation and essentially doubling both caterpillar densities and accumulated herbivory levels on host oak trees. These short-lived but massive emergence events help us to understand how resource pulses can rewire interaction webs and disrupt energy flows in ecosystems, with potentially long-lasting effects. (And India has the world’s only other reported species of periodical cicadas!)