Juan Antonio Hernández-Agüero*, Mechthilde Falkenhahn, Jessica Hetzer, Karsten Wesche, Christiane Zarfl, Klement Tockner.

Background

Oases are azonal, highly productive, densely vegetated areas within drylands, often converted to agriculture, and characterized by significant biocultural diversity. Despite their importance, comprehensive information on the global distribution and biocultural diversity of oases has been lacking.

Methods

To address this gap, a detailed bibliographic search and random forest modeling were combined to create a global map of oases, with a focus on Asia and North Africa (ANA).

Results

In the ANA region, oases cover 1.5% of the dryland area and are populated by 150 million people, with an additional 268 million people living nearby and most likely being dependent on them. Globally, oases contain more than 8,200 vertebrate species, of which 13% are classified as threatened. However, less than 0.5% of their total area is currently under protection, making oases one of the least conserved ecosystems worldwide. These findings highlight the distinct biocultural, ecological, and geopolitical importance of oases, which are increasingly threatened by climate change and direct human impacts. Despite their significance, oases remain undervalued, emphasizing an urgent need for developing adaptative strategies to sustainably manage these pivotal ecosystems.

Krijnen, B. and Hernández-Agüero, J.A.*

Trophic interactions play a key role in maintaining ecological balance. In urban envi-ronments, avian predation has been demonstrated to be particularly important due toits effects on community structure, pest control, and nutrient cycling. As humanityrelies upon ecosystem services for sustenance, and with 70% of the global populationprojected to reside in urban areas by 2050, understanding the impact of urbanizationon avian predation is becoming increasingly important. This study investigates theimpacts of urban microclimates, shaped by impervious surfaces and green/blue infra-structure, and human-induced disturbances, on avian predation in urban areas, withthe aim of testing the increased disturbance hypothesis. To assess the avian predationrate, plasticine caterpillars were placed in Quercus robur trees in the city of Amsterdamfor a period of two months. The analyses evaluated the impact of artificial lighting atnight, human population density, the urban heat island effect, impervious surfaces,vegetation, noise pollution, and water bodies on predation rates. The results indicateda substantial increase in predation during the second month, which was likely causedby an increase in naïve fledglings or elevated ambient temperatures. Noise pollutionwas identified as the most frequent and robust predictor of predation, consistentlyleading to a reduction in predation rates, possibly due to avoidance behavior. Otherpredictors exhibited substantial temporal and spatial variability. The variables relatedto urbanization increased predation in the initial month, suggesting that insectivorousbirds prey on areas with higher illumination and temperature. However, the effectdiminished in the subsequent month, potentially due to the increased daylight hoursor a reduction in heating effects. During the second month, all predictors exhibited anegative effect on predation, thereby supporting the increasing disturbance hypothesis.These findings underscore the complex relationship between urban factors and avianpredation, emphasizing the necessity for mitigation efforts in urban planning.

Zvereva, E.L.* Adroit, B. Andersson, T. Barnett, C.R.A.,  Branco, S., Castagneyrol, B., Chiarenza, G.M.,  Dáttilo, W.,  del-Val, E., Filip, J., Griffith, J.,  Hargreaves, A.,  Hernández-Agüero, J.A., Holanda, I.,  Hong, Y.,  Kietzka, G., Klimez, P.,  Koistinen, M., Kruglova, O., Kumpula, S., Lopezosa, P.,  March-Salas, M., Marquis, R. J.,  Marusik, Y.M.,  Moles, A.,  Muola, A.,  Murkwe, M.,  Nakamura, A., Olson, C.,  Pagani-Núñez, E.,  Popova, A.,  Rahn, O., Reshchikov, A.,  Rodriguez-Campbell, A.,  Rytkönen, S.,  Sam, K.,  Sounapoglou, A.,  Tropek, R.,  Wenda, C.,  Xu, G., Zeng, Y.,  Zolotarev, M.,  Zubrii, N.,  Zverev, V. & Kozlov, M.V.

Aim: The long-standing Latitudinal Biotic Interaction Hypothesis (LBIH) states that the intensity of biotic interactions increases from high to low latitudes, but individual studies find varied latitudinal patterns. Studies addressing geographic variation in predation on insect prey have often relied on prey models, which lack many biological characteristics of live prey. Our goals were to test LBIH for predator attack rates on standardised live insect prey and to compare the revealed latitudinal patterns in predation with patterns obtained on plasticine prey models. Location: Global. Time period: 2021‒2023. Major taxa: Arthropods, birds. Methods: We measured predation rates in 43 forested sites distributed in five continents from 34.1°S to 69.5°N latitude. At each site, we exposed 20 sets of three baits, one set per tree. Each set included three live fly larvae (maggots), three live fly puparia and three plasticine models of these puparia. Half of the sets were isolated from non-flying predators by glue rings. Results: Arthropod attack rates on plasticine prey decreased linearly from low to high latitudes, while attack rates on maggots showed a U shaped distribution, with the lowest predation at temperate latitudes. This difference emerged from intensive predators attacks on live prey, but not on artificial prey, in boreal forests (latitudes exceeding 59.5°). Site-specific attack rates of arthropod predators on live and plasticine prey did not correlate with each other. In contrast to arthropods, bird predation rates on live and plasticine prey were positively correlated, but did not show significant latitudinal patterns. Main conclusions: Latitudinal patterns in predation differ between major groups of predators and between types of prey. Poleward decreases in both arthropod and total predation on plasticine models do not mirror patterns observed on live prey, the latter likely reflecting real patterns of predation risk better than do patterns of attack on artificial prey.

Juan Antonio Hernandez-Agüero, Ildefonso Ruiz-Tapiador,  Lucas A. Garibaldi,  Mikhail V. Kozlov,  Elina Mantyla,  Marcos E. Nacif,  Norma Salinas & Luis Cayuela

Aim: Global-scale studies are necessary to draw general conclusions on how trophic interactions vary with urbanization and to explore how the effects of urbanization change along latitudinal gradients. We predict that the intensity of trophic interactions decreases in response to urbanization (quantified by human population density). Since trophic interactions are more intense at lower latitudes, we also expect major impacts of urbanization at higher latitudes, where base levels are essentially lower.  Location: Global (881 study sites). Time period: 2000-2021. Major taxa studied: Birds, arthropods and woody plants.  Methods: We compiled global data on insect herbivory and bird predation from studies that employed similar methods, and fitted generalized linear mixed models to test how these trophic interactions vary with human population density, latitude, and their interaction. Results: The intensity of herbivory and predation decreased with an increase of human population density at lower latitudes. Surprisingly, it remained unaffected at intermediate latitudes and even increased at higher latitudes. Main conclusions: The observed patterns may be attributed to local climate changes in urban areas, such as the Urban Heat Island effect, which disrupts the thermal stability in the tropics while increasing niche availability at polar latitudes.

Juan Antonio Hernández-Agüero*, Ildefonso Ruiz-Tapiador, Eric Cosio Lucas A. Garibaldi, Mikhail V. Kozlov, Marcos E. Nacif, Norma Salinas, Vitali Zverev, Elena L. Zvereva & Luis Cayuela

Forest management can affect both the functioning and stability of ecosystems. These effects can be highly variable and change across forest ecosystems. We studied the effects of forest management on the strength of resource–consumer interactions (bird predation and insect herbivory) as important measures of ecosystem functioning, as well as on their stability throughout the years in four different forested regions (Andean forest, boreal forest, Mediterranean forest, and Patagonian forest). Within each region, we selected (i) heavily managed or plantation forests, and (ii) urban/peri-urban forests or urban plantings and paired them with pristine/semi-natural forests. The probability of bird predation was estimated using Plasticine caterpillars with different colors. The proportions of chewer, galler, and miner herbivory on leaves were estimated for 15 plants (shrubs and trees) per study site. Ecosystem stability was quantified as the invariability of both predation and herbivory during a period of three years. We found no consistent responses in terms of either predation or herbivory to forest management practices across forest ecosystems. Bird predation was higher in urban/peri-urban forests than pristine/semi-natural forests in Patagonian and boreal forest, with intermediate levels of predation in managed or plantation forests. Chewing insect herbivory was higher in managed or plantation and pristine/semi-natural forests than urban/peri-urban forests, but no differences were found in other types of herbivory. These differences might be explained by the contrasting temperatures between urban and non-urban areas (i.e., urban heat effect) affecting the performance of ectotherm species, but also by the differences in climate and species compositions among regions. In addition, we consistently found no effects of forest management practices on predation invariability and herbivory, thereby demonstrating the high resilience of forests to different management practices across regions. These findings improve our knowledge of the generalized effects of forest management on ecosystem functions and stability by establishing a connection between the ecology and management and conservation of plantations and natural forests.

Inés María Alonso-Crespo & Juan Antonio Hernández-Agüero*

Interactions between species within an ecosystem (e.g. predation and herbivory) play a vital role in sustaining the ecosystem functionality, which includes aspects like pest control and nutrient cycling. Unfortunately, human activities are progressively disrupting these trophic relationships, thereby contributing to the ongoing biodiversity decline. Additionally, certain human activities like urbanization may further impact the intensity of these trophic interactions, which are already known to be influenced by latitudinal gradients. The aim of this study was to test the hypothesis of whether the impact of human population, used as a proxy for human pressure, differs between latitudes. To test it, we selected 18 study sites at two latitudes (i.e. ~53°N and ~50°N) with varying human population density (HPD). We used artificial caterpillars placed on European beech branches to assess bird predation and took standardized pictures of the leaves to estimate insect herbivory. Remote sensing techniques were used to estimate human pressure. We found that the intensity of bird predation varied in response to HPD, with opposite trends observed depending on the latitude. At our upper latitude, bird predation increased with HPD, while the opposite was observed at the lower latitude. Herbivory was not affected by urbanization and we found higher levels of herbivory in the lower compared to the higher latitude. At the lower latitude, certain species may experience a disadvantage attributed to the urban heat island effect due to their sensitivity to temperature fluctuations. Conversely, at the higher latitude, where minimum temperatures can be a limitation, certain species may benefit from milder winters. Overall, this study highlights the complex and dynamic nature of trophic relationships in the face of human-driven changes to ecosystems. It also emphasizes the importance of considering both human pressure and latitudinal gradients when assessing the ecological consequences of future climate change scenarios, especially in urban environments.

Laura Tydecks, Juan Antonio Hernández-Agüero*, Katrin Böhning-Gaese, Vanessa Bremerich, Jonathan M. Jeschke, Brigitta Schütt, Christiane Zarfl & Klement Tockner

The diversity of life sensu lato comprises both biological and cultural diversity, described as “biocultural diversity.” Similar to plant and animal species, cultures and languages are threatened by extinction. Since drylands are pivotal systems for nature and people alike, we use oases in the Sahara Desert as model systems for examining spatial patterns and trends of biocultural diversity. We identify both the underlying drivers of biodiversity and the potential proxies that are fundamental for understanding reciprocal linkages between biological and cultural diversity in oases. Using oases in Algeria as an example we test current indices describing and quantifying biocultural diversity and identify their limitations. Finally, we discuss follow-up research questions to better understand the underlying mechanisms that control the coupling and decoupling of biological and cultural diversity in oases.

Oleksandra Shumilova*, Klement Tockner, Alexander Sukhodolov, Valentyn Khilchevskyi, Luc De Meester, Sergiy Stepanenko, Ganna Trokhymenko, Juan Antonio Hernández-Agüero & Peter Gleick 

The armed conflict between Ukraine and Russia that began in late February 2022 has far-reaching environmental consequences, especially regarding water resources and management. Here we analysed the multifaceted impacts of the military actions on freshwater resources and water infrastructure during the first three months of the conflict. We identified the nature of the impacts, the kind of pressures imposed on the water sector and the negative consequences for the availability and quality of freshwater resources for the civilian population. Our results showed that many water infrastructures such as dams at reservoirs, water supply and treatment systems and subsurface mines have been impacted or are at risk from military actions. Continuation of the conflict will have multiple negative sustainability implications not only in Ukraine but also on a global scale, hampering achievement of clean water and sanitation, conservation and sustainable use of water resources, and energy and food security.

Martí March-Salas*, Felipe Morales-Armijo, Juan Antonio Hernández-Agüero, Eduardo Estrada-Castillón, Andrea Sobrevilla-Covarrubias, José Ramón Arévalo, J. F. Scheepens & Juan Lorite 

Cliffs are unique ecosystems with an outstanding but relatively unknown plant diversity, harboring rare, endemic and threatened species, but also rock-specialist or generalist species that can become locally common and dominant on cliffs. The rising popularity of climbing represents an increasing threat to cliff biota, affecting community composition and potentially diminishing diversity and species associations. We used a novel sampling design of closely-paired climbed versus unclimbed points along the cliff-face. We sampled along climbing routes of different climbing intensities in El Potrero Chico (Nuevo León, Mexico), identifying plant species and analyzing species associations and community composition in climbed and unclimbed plots. Diversity on the sampled cliffs was high, even greater than in other regional ecosystems. We found reduced abundance, cover, and diversity in climbed plots, irrespective of climbing intensity. Dominant species on the sampled cliffs were the most negatively affected by rock climbing in terms of abundance, and some locally rare species, including endemics and endangered species, were entirely absent from climbed plots. Co-occurrence analysis showed that the number of associations between pairs of dominant and common species were greatly reduced in climbed plots, and that positive associations between locally rare species existed in unclimbed plots but not in climbed plots, which may contribute to the disappearance of endemic and threatened species. Finally, NMDS analysis revealed that the community composition changed significantly due to climbing. Our results indicate that conservation science should convince stakeholders of the need for a holistic conservation of cliff ecosystems and not focus solely on emblematic or rare species, since plant community dynamics and preservation depend on interactions between plant species.

Juan Antonio Hernández-Agüero*, Ildefonso Ruiz-Tapiador & Luis Cayuela 

Aim: Holm oak (Quercus ilex L.) is regarded as a keystone plant species. Trophic interactions may affect the distribution and abundance of phytophagous species, but the number of arthropod species that use holm oak as a food resource and their levels of host specificity are not yet known. Here, we aimed to quantify these species, their feeding strategies and conservation status, the taxonomic relatedness in each trophic guild and their degree of host specificity on holm oak. Location: Our study covered the whole distribution area of Q. ilex in the central-western Mediterranean Basin. Methods: We reviewed the existing literature and compiled information about all arthropod species that feed on Q. ilex, as well as their feeding strategies and conservation status. We also investigated the relationships between trophic guilds and the taxonomic relatedness of species, and assessed the degree of climatic niche overlap with holm oak. Results: We found that 605 species feed on seven different parts of the holm oak plant (i.e. feeding strategies). More than 90% of these species lack a conservation status assessment, and eight are threatened by human activities, either as vulnerable, endangered or critically endangered. A significant phylogenetic relationship was found between taxonomic relatedness and groups of arthropods that feed on the same part of the plant (i.e. trophic guilds). Twenty per cent of the species had similar niches, thereby indicating the potentially high host dependence of these species. Main conclusions: This study highlights the significance of a keystone tree species for arthropod conservation and the need for further research into the distribution and conservation status of arthropod species in Mediterranean holm oak woodlands.

Juan Antonio Hernández-Agüero*, Vicente Polo, Miguel García, Diego Simón, Ildefonso Ruiz-Tapiador & Luis Cayuela

Prey detection and selection by birds can be influenced by prey coloration. Whereas certain colours can indicate to predators the unpalatability of prey (i.e. aposematism), other colours can render prey cryptic against the background. However, there are discrepancies in the response of birds to prey coloration reported in different studies. Such discrepancies can be the result of geographical or temporal (e.g. seasonal) differences between studies if birds in different regions respond differently to coloration or if responses vary seasonally due to changes in bird composition. Experimental studies aiming to understand bird responses to prey colour should consider the effect of geographical variation while accounting for seasonal as well as interannual variability. We investigated the effects of colour on attack rates by exposing plasticine caterpillars of different colours to bird communities in 13 Mediterranean forests in central Spain for a period from 17 weeks to 7 months. Overall, yellow and green dummy caterpillars suffered the lowest attack rates. We also observed a bimodal pattern of bird attack rates through time, with highest predation occurring in late winter and summer (June to September). Low attack rates on yellow dummies are probably a consequence of aposematism, while low attack rates on green dummies probably resulted from crypsis. Rapid decreases in attack rates over time are probably a result of avoidance learning, whereas the increase in attacks in summer could be explained by the increase in fledglings and migrant birds.

Rodrigo Megía-Palma*, Octavio Jiménez-Robles, Juan Antonio Hernández-Agüero & Ignacio De la Riva 

The plastic capability of species to cope with the new conditions created by climate change is poorly understood. This is particularly relevant for organisms restricted to high elevations because they are adapted to cold temperatures and low oxygen availability. Therefore, evaluating trait plasticity of mountain specialists is fundamental to understand their vulnerability to environmental change. We transplanted mountain lizards, Iberolacerta cyreni, 800 m downhill to evaluate the plastic response in body condition, thermoregulation traits, haemoglobin level, and haemoparasite load. Initial measurements of body mass, total haemoglobin concentration ([Hb]), hematic parasite intensities, dorsal luminance, and thermoregulatory behaviour were resampled after two and four weeks of acclimation. We also tested whether an anti-parasitic drug reduced haemoparasite intensity. After only two weeks of acclimation to a lower elevation, lizards decreased 42% in [Hb], had 17% less parasite intensities, increased body condition by 25%, and raised by ~3% their mean preferred temperatures and their voluntary thermal maximum. The anti-parasitic treatment had no significant effect on the intensity of hematic parasites, but our results suggest that negative effects of haemoparasites on [Hb] are relaxed at lower elevation. The rapid plastic changes observed in thermal preferences, body condition, [Hb], and parasite intensity of I. cyreni demonstrate a potential plastic response of a mountain specialist. This may be adaptive under the climatic extremes typical of mountain habitats. However, there is uncertainty in whether the observed plasticity can also help overcome long term environmental changes.

Elena L Zvereva*, Bastien Castagneyrol, Tatiana Cornelissen, Anders Forsman, Juan Antonio Hernández‐Agüero, Tero Klemola, Lucas Paolucci, Vicente Polo, Norma Salinas, Kasselman Jurie Theron, Guorui Xu, Vitali Zverev & Mikhail V Kozlov

The strength of biotic interactions is generally thought to increase toward the equator, but support for this hypothesis is contradictory. We explored whether predator attacks on artificial prey of eight different colors vary among climates and whether this variation affects the detection of latitudinal patterns in predation. Bird attack rates negatively correlated with model luminance in cold and temperate environments, but not in tropical environments. Bird predation on black and on white (extremes in luminance) models demonstrated different latitudinal patterns, presumably due to differences in prey conspicuousness between habitats with different light regimes. When attacks on models of all colors were combined, arthropod predation decreased, whereas bird predation increased with increasing latitude. We conclude that selection for prey coloration may vary geographically and according to predator identity, and that the importance of different predators may show contrasting patterns, thus weakening the overall latitudinal trend in top-down control of herbivorous insects.

Juan Antonio Hernández-Agüero* &  Rodrigo Manuel Megía Palma

Juan Antonio Hernández-Agüero* & Sonia Plasencia