Shedding light on trophic interactions: A field experiment on the effect of human population between latitudes on herbivory and predation patterns.

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.

Las interacciones entre especies dentro de un ecosistema (p. ej., depredación y herbivoría) juegan un papel vital en el mantenimiento de la funcionalidad del ecosistema, incluyendo aspectos como el control de plagas y el ciclo de nutrientes. Desafortunadamente, las actividades humanas están interrumpiendo progresivamente estas relaciones tróficas, contribuyendo así a la continua disminución de la biodiversidad. Además, ciertas actividades humanas, como la urbanización, pueden afectar aún más la intensidad de estas interacciones tróficas, que ya se sabe que están influenciadas por gradientes latitudinales. El objetivo de este estudio fue probar la hipótesis de si el impacto de la población humana, utilizada como indicador de la presión humana, difiere entre latitudes. Para probarlo, seleccionamos 18 sitios de estudio en dos latitudes (es decir, ~53°N y ~50°N) con densidad de población humana (HPD) variable. Utilizamos orugas artificiales colocadas en ramas de haya común para evaluar la depredación de aves y tomamos fotografías estandarizadas de las hojas para estimar la herbivoría de los insectos. Se utilizaron técnicas de teledetección para estimar la presión humana. Descubrimos que la intensidad de la depredación de las aves varió en respuesta al HPD, observándose tendencias opuestas según la latitud. En nuestra latitud superior, la depredación de aves aumentó con HPD, mientras que se observó lo contrario en la latitud inferior. La herbivoría no se vio afectada por la urbanización y encontramos niveles más altos de herbivoría en la latitud inferior en comparación con la superior. En latitudes bajas, ciertas especies pueden experimentar una desventaja atribuida al efecto de isla de calor urbano debido a su sensibilidad a las fluctuaciones de temperatura. Por el contrario, en latitudes más altas, donde las temperaturas mínimas pueden ser una limitación, ciertas especies pueden beneficiarse de inviernos más suaves. En general, este estudio destaca la naturaleza compleja y dinámica de las relaciones tróficas frente a los cambios en los ecosistemas provocados por el hombre. También enfatiza la importancia de considerar tanto la presión humana como los gradientes latitudinales al evaluar las consecuencias ecológicas de los futuros escenarios de cambio climático, especialmente en entornos urbanos.

Oases in the Sahara Desert-Linking biological and cultural diversity.

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.

Opposite latitudinal patterns for bird and arthropod predation revealed in experiments with differently colored artificial prey.

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.