Acta Oecologica

Assessing the resistance of a breeding amphibian community to a large wildfire Publication date: August 2019 Source: Acta Oecologica, Volume 99 Author(s): Alberto Muñoz, Ángel M. Felicísimo, Xavier Santos Abstract Socioeconomic and global climate changes are modifying fire regimes towards larger and more intense fires. Studying the response of organisms to the occurrence of large fires is crucial to anticipate shifts in patterns of biodiversity in fire-prone regions. Amphibia is the most threatened terrestrial vertebrate taxon, although it is also the least studied in relation to its response to fire. We evaluated the resistance to fire (similarity in species composition before and after fire) and reproductive success during the first breeding season after a fire of an amphibian community at the Mediterranean basin. We sampled 33 aquatic habitats, including ponds and streams located inside and outside the perimeter of the fire, and reported the presence of adult amphibians and their reproductive success. The community composition in burnt and unburnt areas was compared by similarity analysis. Generalized Linear Models were used to test the effects of fire (burnt or unburnt area), habitat type (stream or pond), distance to the perimeter of the wildfire, and altitude on total and breeding species richness. We did not find significant differences in amphibian community composition between burnt and unburnt areas, or in total species richness per water point. Of the 12 species found in the study area, only frogs of the genus Hyladeclined in the burnt area due to the destruction of their preferred microhabitat, i.e. vegetation surrounding ponds. In contrast, breeding occurrence and breeding species richness declined in burnt streams and ponds. These results suggest a high amphibian resistance to fire at the community level, although the reduction of breeding activity can threaten the persistence of a rich community in future scenarios of increased recurrence of megafires.

Seabirds modify trophic groups, while altitude promotes xeric-tolerant species of Tardigrada in the high Arctic tundra (Svalbard archipelago) Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Krzysztof Zawierucha, Katarzyna Zmudczyńska-Skarbek, Noemi Guil, Michał Bogdziewicz Abstract In the Arctic, especially in the coastal mountainous areas, gradual changes in elevation above sea level and allochthonous nutrients delivered by seabirds modify environmental conditions. Increasing elevation affects temperature whereas allochthonous nutrients delivered by seabirds to the terrestrial ecosystem remarkably influence primary production and diversity of organisms. Knowing the abundance of ubiquitous tardigrades (a microinvertebrate phylum), their multitrophic level function and their trophic composition might be essential for understanding ecosystem functioning and matter flow in fragile polar ecosystems. In this study, we tested the effects of altitude and seabird guano on modifying trophic diversity of tardigrades. We found that the tardigrades in Hornsund were herbivorous and microbivorous species dominated. Microbivores were significantly more abundant in guano-supplied than in control areas, which may be explained by the presence of higher nutrient and organic matter content in comparison with areas not fertilised by birds. We observed no significant relationship between the abundance of tardigrade trophic groups and altitude. However, the abundance of xeric-tolerant herbivorous terrestrial tardigrades representing the class Heterotardigrada increased with altitude. Strongly hygrophilic conditions (ponds, swamps, streams) at lower elevations as well as acidic conditions formed by seabird guano may reduce the abundance of heterotardigrades. Our study shows that seabirds rather than the effect of altitude or the generally predicted increasing temperatures in the Arctic, are affecting high Arctic tundra limno-terrestrial invertebrate trophic groups proportion. Our results provide baseline data for future studies of the Hornsund region, since climate change scenarios predict decreased guano delivery by seabirds on mountain slopes, shifts in plant species dominance and more intense fertilisation of lakes by geese, all of which may alter invertebrate trophic composition in southern Svalbard.

Complex effects of nonpollinating wasps on the relationship between pollinating wasp and seed production in Ficus andicola Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): William Cardona, Gustavo H. Kattan Abstract Mutualisms are evolutionarily unstable because an imbalance in benefits obtained by the two partners may make the interaction exploitative. In the Ficus-Agaonidae system, it is advantageous for pollinating wasps (PW) to lay eggs in as many flowers as possible within a fig, to maximize offspring production. From the tree's perspective, however, a balance is expected between seed and wasp production, as wasps represent the tree's male function. The key to the system's stability requires explaining why PW mainly use internal flowers for egg-laying, leaving those closer to the fig's wall for seed production. An hypothesis proposes that nonpollinating fig-wasps (NPFW), which exploit the system by laying eggs in figs but not pollinating, help stabilize the mutualism. We compared seed and PW production in figs of F. andicola with and without NPFW. In unexploited figs, seed and PW numbers were negatively correlated, and the PW/seeds proportion was 3:1. In exploited figs, seed and PW numbers were positively correlated, and the PW/seed ratio was approximately 1:1. This pattern may result from an indirect effect of Idarnes gr. flavicollis on PW. This species of NPFW lays before or simultaneously with PW in the same kind of flowers, causing PW to spend more time searching for free ovaries, thus reducing their laying rate. Alternatively, PW may reject some flowers to reduce the risk of exploitation by NPFW. In unexploited figs, PW use more flowers at the expense of seed production. In exploited figs, NPFW restrict flower use by PW, favoring a balance in the seeds/PW ratio. This effect only occurs at low exploitation levels. The absence of NPFW favors PW, whereas high exploitation levels are detrimental for both seeds and PW. A high spatial and temporal variability in exploitation rates seems required to avoid directional selection favoring PW or NPFW, thus stabilizing the mutualism.

Dietary composition and selection in the stream-breeding anuran assemblage from a tropical wet forest in eastern Mexico Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Ricardo Luría-Manzano, Aurelio Ramírez-Bautista Abstract In this study, we analyzed seasonal variation in dietary composition and diversity, structure along the trophic axis, and prey selection in a stream-breeding anuran assemblage from Mexico. It is composed of four morphologically diverse species: three strictly arboreal (Hyalinobatrachium fleischmanni, Ptychohyla zophodes, and Rheohyla miotympanum) and one that occupies several microhabitats (Lithobates vaillanti). Dietary composition did not differ between seasons, but it differed among the four species. Araneae, Orthoptera, Homoptera, and Lepidoptera (adults) were the prey that accounted for most of the variation. Dietary diversity was higher in the dry than in the rainy season in L. vaillanti, and was higher in this species than in the other three. In the dry season, arthropods were more abundant but less diverse in the environment, and L. vaillanti and R. miotympanum consumed less prey than in the rainy season. Furthermore, we detected that the frog assemblage was nonrandomly structured only in the dry season. Hyalinobatrachium fleischmanni strongly selected Homoptera and Orthoptera, but did not select prey by their size within the size range consumed. Ptychohyla zophodes and R. miotympanum strongly selected Lepidoptera (adults and larvae) and selected their prey by their size in the dry season. Our results overall suggest that interspecific competition could be a strong force in shaping type and quantity of food consumed between the two hylids. Additionally, we found a wider array of microhabitats used and prey types consumed than previously reported for L. vaillanti. Lastly, the relatively specialized diet of the three strictly arboreal species, and their selection towards insects sensitive to habitat changes (homopterans and lepidopterans), make them particularly vulnerable to changes in arthropod communities.

Tolerance to severe browsing of three shrub species on Mediterranean islands Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Jordi Bartolomé Filella, Elena Baraza Ruíz, Ma Carme Espunya Prat, Eva Castells Caballé, Leidy Rivera Sánchez, Ma José Broncano Atencia Abstract Buxus balearica Lam., Ephedra fragilis Desf., and Juniperus oxycedrus L. are three Pre-Mediterranean shrubs that have become scarce in the Balearic Islands probably due to a climatic change and the anthropogenic activities during the second half of the Holocene. In addition, an endemic artiodactyl, Myotragus balearicus, exerted browsing pressure on these species for thousands of years, and after it disappeared domestic goats were introduced by humans. Adaptations that enable these plants to resist grazing are structural or chemical; however, there is no information about whether their defenses are only constitutive or also inducible. Currently, the mountain ranges of Majorca Island are extensively occupied by feral goats, and a possible increase in the stocking rates could affect the survival of these plant species. The aim of this study was to evaluate and compare the effects of simulated severe browsing on the re-growth capacity and chemical composition of these species in order to determine their tolerance to herbivory. We sampled and compared structural and chemical variables of saplings submitted to two pruning intensities for each species. The results showed that all three species could maintain their growth rate and biomass ratios under simulated herbivory. Sprout production was also stimulated in all them. E. fragilis and B. balearica increased phenolic content after pruning, and E. fragilis also increased the condensed tannins. Pruning treatments did not trigger induction of phenolic content in J. oxycedrus, which could be considered as a constitutive defense. It is noteworthy that alkaloids in E. fragilis decreased with the treatments, which may contribute to preventing a possible addiction to these compounds, and thus reduce browsing damage. The responses induced by pruning show that these species are very tolerant to a level of herbivory, which could indicate a good adaptation to browsing pressure, exerted since the Pleistocene by Myotragus balearicus, and followed by goats during the last millennia. This is especially relevant in Mediterranean islands, such as the Balearic Islands, where practices for conserving relict plant species are based on feral herbivore exclusion.

Alpine grassland degradation reduced plant species diversity and stability of plant communities in the Northern Tibet Plateau Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Congyan Wang, Mei Wei, Bingde Wu, Shu Wang, Kun Jiang Abstract The alpine grassland in the Northern Tibet Plateau has been degraded in recent decades. This study aimed at addressing the effects of the degree of degradation on species diversity and stability of plant communities and the relationships between diversity stability. Stability of plant communities decreased with the increasing degree of degradation probably due to the significantly decreased diversity and evenness of plant communities with degradation. Diversity (including Shannon and Simpson diversity, Pielou evenness, and species richness) was positively correlated with the corresponding stability of plant communities. This suggets that high levels of plant diversity lead to higher levels of complementary resource use via niche complementation. The relative abundance of the most dominant species was negatively correlated with the stability of the corresponding plant communities. This suggests that the stability of plant communities decreases with increasing degradation but the relative abundance of the most dominant species increases with degradation. In conclusion, diversity and the corresponding stability of plant communities decrease with increasing degradation in the alpine grassland in the Northern Tibet Plateau.

Earthworms contribute to ecosystem process in no-till systems with high crop rotation intensity in Argentina Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): J.C. Bedano, F. Vaquero, A. Domínguez, M.P. Rodríguez, L. Wall, P. Lavelle Abstract In the Pampas region of Argentina agriculture is dominated by intensive no-till (NT) soybean cropping which produce negative consequences on soil quality. A group of farmers started to use the Good Agricultural Practices (GAP) which include a higher crop rotation, use of winter cover crops and nutrient restoration. In this NT system earthworms have a significant role in soil functioning, particularly in organic matter cycling and soil structure formation. The aim of this paper was to examine the contribution of earthworm activity to the process of C incorporation and soil structure maintenance in soils with different NT variants of: NT with GAP for 30 years (NT + r30); NT with some of the GAP for 12 years (NT-r12) and NT with soybean monoculture (NTm). Also a natural grassland (NA) was sampled as a reference. Earthworm aggregates were obtained by gently separating them from surrounding soil. Fine (HOC) and coarse (POC) organic matter fractions, water-stable aggregates (WSA) and mean weight diameter (MWD) were calculated for earthworm aggregates and bulk soil. In all sites only one species (Aporrectodea caliginosa) was found, with higher density in the NA, followed by NT + r30, that had about 9 times more earthworms than NTm. The number of earthworm aggregates was higher in the NT + r30 followed by the NA, both showing differences with the other NT systems. The earthworm aggregates in NA and NT + r30 had significantly more POC than the surrounding soil (230% increase in NA and 100% NT + r30). Earthworm casts had higher values of MWD and WSA than physical soil aggregates in both NA and NT + r30 management treatments. Our results show the existence of a positive feedback loop we called earthworm-driven virtuous cycle. The increase in earthworm abundance promotes higher production of earthworm aggregates which are richer in organic matter and more water stable than the surrounding soil. This has favourable results in terms of soil quality but also increase crop yields (57% in maize and 18% in soybean), by means of biologically mediated soil processes, which is a highly desirable way to sustainability of agricultural production. Farmers, politicians and the whole society should pay more attention to soil as a key component supporting agricultural production by means of internal biological soil functioning.

Heterogeneity in millipede communities (Diplopoda) within a forest–forest edge–meadow habitat complex Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Slavomír Stašiov, Vladimír Kubovčík, Marek Čiliak, Andrea Diviaková, Ivan Lukáčik, Vladimír Pätoprstý, Martin Dovciak Abstract The positive influence of heterogeneity in vegetation and land-use on animal diversity is generally well established, but it has not been conclusively confirmed yet in millipede communities inhabiting karst canyons where biodiversity is to large extent determined by variation in topography (e.g., elevation). We studied how millipede assemblages (Diplopoda) vary between forest, forest edge, and meadow habitats in this specific karst environment. We sampled millipedes by pitfall trapping during two vegetation seasons (from March to October in 2001 and 2002) in approximately monthly intervals across nine sites in Central Slovakia (Veľká Fatra Mts). In total, 951 individuals belonging to 12 species from 6 families and 10 orders were collected. The dominant species was Unciger foetidus, which was also one of the two most frequent species along with Polydesmus complanatus. Although the total number of captured millipedes was greatest on forest edges (395 individuals), intermediate in meadows, and lowest in forests (214 individuals), millipede abundance and species composition varied considerably within each habitat type among the sites. Total millipede species richness in meadow and forest edge habitats was the same (11 species) and it was lower in forest habitats (7 species), while species diversity (Shannon's H′) and equitability (E) were greatest in meadows. Millipede diversity measures (species richness or equitability) were correlated positively with species richness of herb layer and negatively with shrub layer equitability, soil conductivity, and soil phosphorus. Thus, we found complex patterns of heterogeneity in millipede community composition and richness across studied habitats and elevations that were driven by habitat type and plant community and soil characteristics. While millipede abundance patterns varied, open habitats supported most species-rich millipede communities at lower elevations, while forest edges were most species-rich at the high elevation.

Fear alone reduces energy processing by resident 'keystone' prey threatened by an invader; a non-consumptive effect of 'killer shrimp' invasion of freshwater ecosystems is revealed Publication date: July 2019 Source: Acta Oecologica, Volume 98 Author(s): Calum MacNeil, Mark Briffa Abstract Non-consumptive effects (NCEs) of predators – so called 'fear' responses – encompass costly antipredator behaviours, such as reduced feeding efficiency. NCEs can influence prey population dynamics and community structure, if prey are 'keystone' species such as Gammarus spp. amphipod 'shrimps'. These freshwater macroinvertebrates have the ecosystem functional role of shredding fallen leaf litter, making it accessible to other taxa. Across Europe, the invasive predatory 'killer shrimp' Dikerogammarus villosus is replacing resident Gammarus spp., potentially threatening this vital ecosystem function. While predation (consumptive effects (CEs)) of this invader has been well studied, for the first time we test whether NCEs can be evident in prey only exposed to D. villosus presence and whether this could potentially impact on the prey's functional role. In mesocosms, exposure to constrained D. villosus did not result in mortalities of any of three Gammarus prey species but the leaf shredding efficiencies of all prey were significantly reduced compared to a control treatment. This clear NCE has the potential to propagate through the ecological community via decreased energy processing. This study demonstrates the potential for fear of invasive predator presence alone to impact on ecosystem function.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
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6948891480

alsfakia@gmail.com