Antonios D. Mazaris

Different male vs. female breeding periodicity helps mitigate offspring sex ratio skews in sea turtles

The implications of climate change for global biodiversity may be profound with those species with little capacity for adaptation being thought to be particularly vulnerable to warming. A classic case of groups for concern are those animals exhibiting temperature-dependent sex-determination (TSD), such as sea turtles, where climate warming may produce single sex populations and hence extinction. We show that, globally, female biased hatchling sex ratios dominate sea turtle populations (exceeding 3:1 in >50% records), which, at-a-glance, reiterates concerns for extinction. However, we also demonstrate that more frequent breeding by males, empirically shown by satellite tracking 23 individuals and supported by a generalized bio-energetic life history model, generates more balanced operational sex ratios (OSRs). Hence, concerns of increasingly skewed hatchling sex ratios and reduced population viability are less acute than previously thought for sea turtles. In fact, in some scenarios skewed hatchling sex ratios in groups with TSD may be adaptive to ensure optimum OSRs.

Evaluating the Connectivity of a Protected Areas' Network under the Prism of Global Change: The Efficiency of the European Natura 2000 Network for Four Birds of Prey

Climate and land use changes are major threats to biodiversity. To preserve biodiversity, networks of protected areas have been established worldwide, like the Natura 2000 network across the European Union (EU). Currently, this reserve network consists of more than 26000 sites covering more than 17% of EU terrestrial territory. Its efficiency to mitigate the detrimental effects of land use and climate change remains an open research question. Here, we examined the potential current and future geographical ranges of four birds of prey under scenarios of both land use and climate changes. By using graph theory, we examined how the current Natura 2000 network will perform in regard to the conservation of these species. This approach determines the importance of a site in regard to the total network and its connectivity. We found that sites becoming unsuitable due to climate change are not a random sample of the network, but are less connected and contribute less to the overall connectivity than the average site and thus their loss does not disrupt the full network. Hence, the connectivity of the remaining network changed only slightly from present day conditions. Our findings highlight the need to establish species-specific management plans with flexible conservation strategies ensuring protection under potential future range expansions. Aquila pomarina is predicted to disappear from the southern part of its range and to become restricted to northeastern Europe. Gyps fulvus, Aquila chrysaetos, and Neophron percnopterus are predicted to locally lose some suitable sites; hence, some isolated small populations may become extinct. However, their geographical range and metapopulation structure will remain relatively unaffected throughout Europe. These species would benefit more from an improved habitat quality and management of the existing network of protected areas than from increased connectivity or assisted migration.

Using an individual-based model for assessment of sea turtle population viability

Marine turtle species have a complex life history characterized by interannual variability in reproductive performance and a long life span. These ecological features in combination with the animals’ highly migratory nature create numerous difficulties when trying to assess population dynamics. This study attempts to couple existing information on species demographics and behavioral strategies with simple energetic rules in a theoretical framework. We study sea turtle population dynamics using an individual-based model that incorporates known behavioral-ecological characteristics of the species. Methodology used to design the model was based on the superindividual approach (Scheffer et al. Ecol Model 80:161–170, 1995). We constructed our simulation experiment on a virtual sea turtle population, which was parameterized by using recent literature reviews with emphasis on reproductive parameters of the Mediterranean loggerhead sea turtle population. Switching rules describing critical processes of reproductive performances were established as theoretical functions of efficiency of energy transfer. In order to explore the significance of variable reproductive patterns upon population dynamics and persistence, a series of simulations was performed. The model was also run under fluctuated demographic variables to perform a sensitivity analysis of critical parameters and life-history stages. Based on the specific model parameterization, simulation results show that population persistence was most sensitive to fecundity and to survival at the pelagic juvenile stage. Additionally a surprising finding is the relatively high importance of egg survival in terms of both hatching and hatchling success. We conclude that enhancing the population with new individuals by increasing survival in the early life stages could compensate for additional losses in other age classes. The need for further research regarding biological and behavioral features as well as basic demographic insights into the endangered loggerhead sea turtle is also highlighted.

Spatiotemporal analysis of an acoustic environment: interactions between landscape features and sounds

So far landscape analysis meant analysis of the spatial pattern of land cover or land use. However, biological organisms do not perceive the landscape only as land cover or land use, but they use all their senses, in order to become familiar with and react to their surroundings. We analyzed the acoustic environment as an additional layer of spatial information in landscape analysis, shortening the monopoly of visual patterns as landscape descriptors. We recorded sounds from a rural protected area into seven categories based on their origin, and examined their spatiotemporal variability and their correlation with landscape characteristics. The sounds were distinguished as Foreground or Background sounds. Foreground sounds correspond to sharp sounds originating near the observer and usually are understood as signals of urgent information, triggering reactions; while background sounds carry information over longer distances and may be used as landmarks to help individuals find their bearing even in the absence of visual signs. We found that the acoustic environment varies both temporally and spatially reflecting anthropogenic, geophysical and biological activities. The spatial pattern of the background sounds correlates, to an extent, with the visually perceived landscape features, but it does not correlate with the spatial pattern of the foreground sounds, which do not correlate strongly with the landscape pattern. This spatial pattern mismatch between acoustic environment and landscape, along with the highly dynamic nature of the acoustic environment compared to the relatively static nature of the land cover and land use spatial pattern highlight a limitation of the classical landscape analysis, and expands our understanding of the cognitive landscape.

Spatio-temporal variability in human and natural sounds in a rural landscape

The study of landscape structure and functions, including the underlying ecological and anthropogenic processes has traditionally relied on visual aspects without considering information of non-visionary cues, e.g. auditory. In this work we applied a complementary approach for the study of landscapes using qualitative information for the sonic environment. In particular we studied the qualitative linkages between landscape structure and functions and daily sound patterns. The main objectives were the investigation of the spatial and temporal variability in sound perception, and the identification of the dominant sound categories (anthropogenic, biological, geophysical originated sounds) in relation to landscape characteristics. Our results showed significant spatio-temporal variability in the intensity of different sound categories, which reflects distinct soundscape patterns. Temporal sound variability reflected the daily cycle of anthropogenic activities and biological processes, whereas the spatial sound viability was mainly shaped by landscape attributes. The combination of the visual landscape information and its emergent acoustic profile enhances our perception and understanding of nature and this integrated approach may have many practical applications in landscape management, monitoring and planning.

Phenological response of sea turtles to environmental variation across a species' northern range

Variations in environmental parameters (e.g. temperature) that form part of global climate change have been associated with shifts in the timing of seasonal events for a broad range of organisms. Most studies evaluating such phenological shifts of individual taxa have focused on a limited number of locations, making it difficult to assess how such shifts vary regionally across a species range. Here, by using 1445 records of the date of first nesting for loggerhead sea turtles (Caretta caretta) at different breeding sites, on different continents and in different years across a broad latitudinal range (25–39° ′N), we demonstrate that the gradient of the relationship between temperature and the date of first breeding is steeper at higher latitudes, i.e. the phenological responses to temperature appear strongest at the poleward range limit. These findings support the hypothesis that biological changes in response to climate change will be most acute at the poleward range limits and are in accordance with the predictions of MacArthurs hypothesis that poleward range limit for species range is environmentally limited. Our findings imply that the poleward populations of loggerheads are more sensitive to climate variations and thus they might display the impacts of climate change sooner and more prominently.

Grazing effects on plant functional group diversity in Mediterranean shrublands

Grazing is one of the prevalent human activities that even today are taking place inside protected areas with direct or indirect effects on ecosystems. In this study we analyzed the effects of grazing on plant species diversity, plant functional group (PFG) diversity and community composition of shrublands. We analyzed plant diversity data from 582 sampling plots located in 66 protected areas of the Greek Natura 2000 network, containing in total 1102 plant species and subspecies. We also classified a priori all plant species in seven PFGs: annual forbs, annual grasses/sedges, legumes, perennial forbs, perennial grasses/sedges, small shrubs and tall shrubs. For each site, grazing intensity was estimated in four classes (no grazing, low, medium and high grazing intensity). We found that, at the spatial and temporal scale of this study, as grazing intensity increased, so did total species richness. However, each PFG displayed a different response to grazing. Short-lived species (annual grasses or forbs and legumes) benefited from grazing and their species richness and proportion in the community increased with grazing. Perennial grasses and forbs species richness increased with grazing intensity, but their dominance decreased, since their proportion in the community declined. Short shrub species richness remained unaffected by grazing, while tall shrub diversity decreased. Finally, in sites without grazing the spatial pattern of species richness of the different PFGs was not congruent with each other, while in grazed sites they were significantly positively correlated (with the exception of tall shrubs). This finding may imply that grazing is a selective pressure organizing the community structure, and imposing a certain contribution of each PFG. So, in Mediterranean shrublands in protected areas with a long historical record of grazing, it seems that grazing promotes species diversity and its continuation on a portion of the landscape may be a necessary part of an effective management plan.

Watershed land use types as drivers of freshwater phytoplankton structure

The potential importance of watershed land use types, lake/watershed morphometry/topography and geographic distance as drivers of phytoplankton community composition was evaluated by using data collected from 18 freshwaters (lakes and reservoirs) distributed around Greece. In all freshwaters, phytoplankton species composition showed a strong correlation with the composition of land uses within their watersheds but no correlation with morphometry/topography and geographic distance. Cyanobacteria were found to be associated with artificial and agricultural land use types. Chrysophytes were closely associated to forested areas whereas euglenophytes to industrial, commercial, and transport units. Phytoplankton total biomass was significantly higher in freshwaters with a cover of agricultural and artificial land use >30% in their watersheds. This rather low threshold of agricultural and artificial land use cover might be indicative of the higher sensitivity of Mediterranean freshwaters to eutrophication process. Analysis performed separately for lakes and reservoirs revealed some diverse patterns with lake morphometric/topographic variables significantly affecting similarity in species occurrence. The results demonstrate that land use types reflecting anthropogenic pressures could act as critical drivers explaining phytoplankton structure. Our research suggests that Mediterranean freshwaters could be highly sensitive to land use types within their watersheds, thus landscape structure and configuration should be taken into account toward effective conservation and management plans.

Vegetation coverage change in the EU: patterns inside and outside Natura 2000 protected areas

EU conservation policy is primarily based on the Natura 2000 network of protected areas (PAs). We analyzed the land-cover changes between 2000 and 2006 inside 25,703 Natura 2000 sites in 24 EU Member States, and compared them with those observed outside the PAs. At the EU level, ‘Artificial surfaces’ and ‘Agricultural areas’ exhibit lower rates of transformation within PAs than outside. ‘Forests and semi-natural areas’ marginally increased inside PAs, while they marginally decreased outside. In States that joined the EU before 2000, landscape transformation rates were low, and inside PAs ‘Forest’ preservation was accompanied with a shift from intensive agricultural practices ‘Permanent arable land’ to more diverse ‘Agricultural mosaics’. In new Member States (most of them located in Eastern Europe), there was agricultural abandonment, with conversion to ‘Artificial surfaces’ or ‘Natural vegetation’, both within and outside PAs. Broad scale EU policies (like the Common Agricultural Policy) and socio-economic drivers (like the transition from planned to market economy) seem to be dominant factors in explaining land-cover transformations, while conservation policies may moderate these trends inside PAs.

Dynamics of extinction debt across five taxonomic groups

Species extinction following habitat loss is well documented. However, these extinctions do not happen immediately. The biodiversity surplus (extinction debt) declines with some delay through the process of relaxation. Estimating the time constants of relaxation, mainly the expected time to first extinction and the commonly used time for half the extinction debt to be paid off (half-life), is crucial for conservation purposes. Currently, there is no agreement on the rate of relaxation and the factors that it depends on. Here we find that half-life increases with area for all groups examined in a large meta-analysis of extinction data. A common pattern emerges if we use average number of individuals per species before habitat loss as an area index: for mammals, birds, reptiles and plants, the relationship has an exponent close to a half. We also find that the time to first determined extinction is short and increases slowly with area.