Juan D. Delgado

A review on the effects of alien rodents in the Balearic (Western Mediterranean Sea) and Canary Islands (Eastern Atlantic Ocean)

Invasions of alien rodents have shown to have devastating effects on insular ecosystems. Here we review the ecological impacts of these species on the biodiversity of the Balearic and the Canary Islands. A total of seven species of introduced rodents (two rats, three mice, one dormouse, and one squirrel) have been recorded (six in the Balearics and four in the Canaries). Some of them can occasionally be important predators of nesting seabirds, contributing to the decline of endangered populations in both archipelagos. Rats are also known to prey upon terrestrial birds, such as the two endemic Canarian pigeons. Furthermore, rats actively consume both vegetative and reproductive tissues of a high number of plants, with potential relevant indirect effects on vegetation by increasing erosion and favoring the establishment of alien plants. In the Balearics, rats and mice are important seed predators of endemic species and of some plants with a restricted distribution. In the Canaries, rats intensively prey upon about half of the fleshy-fruited tree species of the laurel forest, including some endemics. In both archipelagos, alien rodents disrupt native plant–seed dispersal mutualisms, potentially reducing the chances of plant recruitment at the same time that they modify the structure of plant communities. We further suggest that alien rodents played (and play) a key role in the past and present transformation of Balearic and Canarian native ecosystems.

Frugivory and factors influencing visitation by birds at "Balo" (Plocama pendula Ait., Rubiaceae) plants in the Canary Islands

We thank many friends for helping us during the fieldwork and laboratory analysis but we would specially like to mention L. Hernandez and M. Gonzalez, P. Jordano offered valuable advice during the planning of this study, as well as during data analysis and interpretation. R. Sallabanks, P. Joprdano, D. Levey, J. Lovett-Doust, and an anonymous referee revised the manuscript and gave very valuable suggestions. Meterorological data were provided by Instituto Nacional de Meteorologia (Canarias Occidentales). We are also grateful to J. Vega for permission to work on Teno bajo. Part of this investigation was supported by the Direccion General de Universidades e Investigacion del Gobierno de Canarias, grant 93/150.

Floristic and structural recovery of a laurel forest community after clear-cutting: A 60 years chronosequence on La Palma (Canary Islands)

We analyzed a post-clearcut chronosequence (0.5 to 60 years after harvesting) in the laurel forest of La Palma island (Canarian Archipelago) to determine the recovery of the stands with respect to species composition, richness, life strategies and structural parameters of the canopy. Multivariate analysis showed that exotic species, as well as annual ruderal species were confined to early-successional stages, while native perennials, typical of laurel forests, dominated the late-successional stages. Total species richness decreased significantly with time after clear-cutting. The relative fast recovery of understory native species may be due to low forest floor disturbance during harvesting. Shade-intolerant pioneer, pioneer-remnant and shade-tolerant late-successional species were the main life strategies of native tree species. Most structural parameters showed a continuous and monotonic increase (basal area, biomass) or decrease (density, percentage of photosynthetic biomass) during succession. Once clear-cutting, here performed with an interval of 8 years, is abandoned, the recovery of the laurel forest seems possible due to careful logging that protects the soil and a rapid asexual regeneration of native tree species, revealing this to be a sustainable management practice.RésuméOn a analysé une chronoséquence après coupe rase (0,5 à 60 ans après récolte) dans la forêt de lauracées de l’île de Palma (Archipel des Canaries) pour déterminer la reconstitution des peuplements pour ce qui concerne la composition spécifique, la richesse et les paramètres structuraux de la canopée. Une analyse multivariable a montré que les espèces exotiques aussi bien que les espèces rudérales étaient confinées aux premiers stades de la succession, tandis que les espèces naturelles pérennes typiques de la forêt de lauracées dominaient les derniers stades de la succession. La richesse spécifique totale a diminué significativement avec le temps après la coupe rase. La reconstitution relativement rapide des espèces naturelles du sous-bois peut être due à la faible perturbation de la surface du sol forestier au moment de la coupe rase. Les pionnières intolérantes à l’ombre, les pionnières rémanentes et les tolérantes à l’ombre des stades finaux de la succession constituaient les principales stratégies des espèces naturelles d’arbres. La plus grande partie des paramètres structuraux ont montré un accroissement continu et monotone (surface terrière, biomasse) ou décroissant (densité, pourcentage de la biomasse photosynthétique) pendant la succession. Autrefois réalisée ici avec un intervalle de 8 ans la coupe rase est abandonnée, la reconstitution de la forêt de lauracées semble possible grâce à une exploitation prudente des bois protégeant le sol et une régénération asexuée des espèces naturelles d’arbres, révélant que ceci est une pratique de gestion durable.

Road Edge Effect and Elevation Patterns of Native and Alien Plants on an Oceanic Island (Tenerife, Canary Islands)

We studied road edge effects on floristic composition and richness of alien and native plants on five zonal ecosystems, following a steep altitudinal gradient from arid coastal and mid-elevation scrublands, through laurel and pine forests, to summit scrub, on Tenerife (Canary Islands). We analyzed vegetation within transects running from the road edge to the core of natural habitats. Alien richness significantly decreased with distance to road edge for most ecosystems. Native richness also decreased with increasing road distance for the coastal scrub and pine forest, but increased for the thermophilous scrub. We found a decrease in both native and alien species richness with elevation. Our results suggest that road edge effects in alien plant invasion are stronger in native shrub communities at low elevations than in forests (laurel and Canary Island pine forest), where aliens were limited to a narrow road edge band. Detrended correspondence analyses showed that road edge plots were floristically very different from interior plots and that each ecosystem harboured a specific alien assemblage with few species present in more than one ecosystem, suggesting a marked species turnover of roadside alien species across altitudinal belts up to the pine forest. However, at high elevations, very few aliens invaded roadsides, probably due to harsh environmental conditions and still relatively low propagule pressure.

Regeneration niche of the Canarian juniper: the role of adults, shrubs and environmental conditions.

Abstract• Canarian Juniper woodlands, now very scarce, are rich in endemic and endangered plants. However, many aspects of juniper regeneration are almost unknown.• This paper relates occurrence and abundance of recruits of Juniperus turbinata ssp. canariensis to (1) small-scale soil characteristics; (2) vegetation cover; and (3) distance to conspecific adults in two contrasting juniper stands in the eastern mountains of Tenerife. We used non-parametric classification trees and generalised linear models (GLM) to evaluate the effect and importance of each explanatory variable on the occurrence of juniper saplings.• Sapling density, vitality and growth rate, as well as fruit production by adult trees, but neither cone density on the ground nor sapling size, varied significantly with respect to slope orientation, representing environmental stress. Within each stand, distance to nearest adult tree was the most important variable explaining the spatial distribution of juniper saplings and availability of seeds in cones. Additionally, saplings were positively associated with shrub cover at the microsite-level, but not with spiny shrub cover. Soil depth and rock cover had a weak negative effect on sapling establishment, but only at the south-facing site and in the open space microhabitat.• Results suggest that recruitment of Canarian juniper is facilitated by microhabitats offered by adults and shrubs. The key factors affecting recruitment are thought to be (1) favourable micro-environmental conditions and (2) high ambient seed availability. Browsing intensity in recent decades was very low. The presence of spiny shrubs did not favour juniper establishment. Facilitation therefore appears to result from amelioration of abiotic conditions rather than from protection against herbivory.

Road edge effects on litter invertebrate communities of subtropical forests

We assessed road edge effects on leaf-litter macroinvertebrates in laurel and pine forests in Tenerife (Canary Islands), studying composition, abundance, richness and diversity, and the role of environmental gradients. We sorted species to the finest taxonomic resolution possible and used a morphospecies approach when necessary. In all, 15,824 invertebrates were identified from 388 litter samples (from >500 species, five major phyla and 31 orders). Alien invasive species of Oligochaeta, Pulmonata, Isopoda, Diplopoda and Hymenoptera were frequent in both forests. Richness, diversity and rarefaction pointed to a disturbance threshold within the first 10 m off the road, and edge effects were steeper in laurel forest than in pine forest. Overabundant aliens were partially responsible for highly disturbed litter assemblages on this edge zone in both forests. Proximity to road edge caused gradients of disturbance of forest structure. Litter moisture, rock and litter cover in laurel forest, and grass and canopy cover in pine forest were the best predictors of community variation. Results seemed to give some empirical support to the intermediate disturbance hypothesis. This altered road edge zone may accumulate regionally causing net reductions of ecosystem area and quality, impacting on its integrity and biodiversity.

Macrofaunal communities of threatened subtidal maërl seabeds on Tenerife (Canary Islands, north-east Atlantic Ocean) in summer

This study contributes with the first data on physical and taxonomical structure of macrofaunal assemblages of maërl beds from the Canary Islands. Maërl beds and Cymodocea nodosa meadows of the Canary Islands are considered biodiversity hot-spots in terms of taxonomic and functional biodiversity with a broad geographical and depth ranges. The authors have studied the structure of the macrofaunal assemblages on different habitat types (Cymodocea, Caulerpa, sabellid field, garden eel and maërl beds). Samples were taken at a range of depths between 14 and 46 m. Correlations were performed among abiotic variables (granulometry, organic matter, nitrogen and phosphates) and the most abundant taxa. Similarity analysis was performed to explore the patchiness of seabeds at a local scale. Significant differences were found in macrofaunal assemblages among seabed types, with highest abundances and lowest biodiversity in sabellid fields, where the sabellid Bispira viola dominated. The polychaetes Aponuphis bilineata and Chone filicauda and the mollusc Turritella brochii were the most abundant taxa on maërl beds. The mosaic of granulometric conditions would explain the associated macroinfaunal community structure and contribute to the creation of diversity on these relatively well preserved seabeds at a local scale.

Bird communities in two oceanic island forests fragmented by roads on Tenerife, Canary Islands

Although most studies on road effects on birds have been conducted on continental grounds, road fragmentation on oceanic islands is often heavier. We assessed variation in bird communities near (≤25 m) and far (>100 m) from forest roads dividing laurel and pine forests on Tenerife, Canary Islands. Line transects were used as the census technique. We compared community structure and species responses between both forests, and among forest interior and edges of paved and unpaved roads. We analysed richness and diversity of species in these different situations, and tested for significance in bird community descriptors and species abundance responses to road proximity. The bird community of the laurel forest showed significantly higher average population density, richness, diversity and evenness than that of the pine forest. None of the two forests showed significant differences in community descriptors between edge and interior, except for a higher evenness along unpaved roads in the laurel forest. However, the bird community showed more overall abundances, richness and diversity on unpaved than on asphalt road edges in laurel forest. Excepting two passerines (Turdus merula in laurel forest and Phylloscopus canariensis in pine forest), all species had similar abundances on road edges and forest interior regardless of forest type. Most species might be regarded as forest generalists. Changes detected between edge and interior on road-fragmented forests were, overall, small at the bird community level. Managers should consider the effects of road edge and road type on the more sensitive species in present and future road planning.

Out of sight, out of mind: threats to the marine biodiversity of the Canary Islands (NE Atlantic Ocean).

Lack of knowledge of the marine realm may bias our perception of the current status and threats to marine biodiversity. Less than 10% of all ecological literature is related to the ocean, and the information we have on marine species that are threatened or on the verge of extinction is scarce. This lack of information is particularly critical for isolated areas such as oceanic archipelagos. Here we review published and grey literature on the current status of marine organisms in the Canary Islands as a case description of the consequences that current out-of-sight out-of-mind attitudes may have on this unique environment. Global change, as represented by coastal development, pollution, exotic species and climate change, are currently affecting the distribution and abundance of Canarian marine organisms, and pose multiple threats to local species and communities. Environmental risks are significant at community and species levels, particularly for threatened species. Failure to address these trends will result in shifts in local biodiversity with important ecological, social, and economic consequences. Scientists, policy makers, educators, and relevant societal groups need to collaborate to reverse deleterious coastal biodiversity trends.

Endorheic currents in ecology: an example of the effects from scientific specialization and interdisciplinary isolation

ABSTRACT Mainstream ecological thought is explored in three sections: (i) Epistemological traits. Given the typical scientific development and the necessity of preserving our intellectual heritage, the conservatism outlined in (i) is cyclical, so its stages are graphically summarized. (ii) Methodological benchmarks antithetically derived from (i), in order to get faster advancement consistent with the growing environmental challenges which spur ecological development. (iii) The renaissance of an old paradigm. This section exposes the misunderstanding of the physical concept of equilibrium by the mainstream ecological thought; this explains its current state. Consequently, section (iii) also summarizes the evolution of a recent set of proposals (organic biophysics of ecosystems) that rescues the foundational paradigm of ecosystem ecology based on physics, neglected by the mainstream thought before producing its most valuable results. We highlight that the main problems emerge from the weakness of integration between ecology, physics and epistemology, and spurious links between ecology and neoclassical economics.