Ecosystem Engineering

Modern African elephants affect habitats and ecosystems in significant ways. They push over trees to feed on upper branches and often peel large sections of bark to eat. These destructive habits sometimes transform woody vegetation into grasslands. Systems of elephant trails may be used and re-used for centuries, and create incised features that extend for many kilometers on migration routes. Elephants, digging in search of water or mineral sediments, may remove several cubic meters of sediments in each excavation. Wallowing elephants may remove up to a cubic meter of pond sediments each time they visit water sources. Accumulations of elephant dung on frequented land surfaces may be over 2 kg per square meter. Elephant trampling, digging, and dust-bathing may reverse stratigraphy at archeological localities. This paper summarizes these types of effects on biotic, geomorphic, and paleontological features in modern-day landscapes, and also describes several fossil sites that indicate extinct proboscideans had very similar effects, such as major sediment disturbances.► Elephants are major sculptors of local land surfaces in Africa ► Elephants may transform woodlands into open mosaics or grasslands ► Elephant dung may accumulate up to 2 kg per square meter in frequented areas ► Fossil sites preserve similar evidence of mammoth behavior

This thesis is an investigation on the niche concept and related theoretical frameworks: niche theory and neutral theory in ecology, niche construction theory in evolutionary biology, and the stem cell niche in intraorganism ecology. The first chapter traces the history of the niche concept and compares niche theory to a competing theory, the neutral theory of biodiversity. The niche concept appears to be an explanans of species diversity and ecosystem structure. The second chapter compares standard evolutionary theory to the theory of niche construction, in which an organism can affect its environment and thus influence the selection to come. I show how to characterize this confrontation in terms of the time scales of the processes involved, which allows us to identify the range of validity truly unique to niche construction theory more explicitly than it has been in the past. The third chapter develops the research of the previous two chapters in the modeling of a gene therapy as a process of competition and ecological niche construction by cells. I present a family of models applied to different time scales of cellular dynamics , among which the careful modeler cannot choose without specific experimental results. I conclude on the conceptions of the relationship between an organism and its environment attached to the various facets of the concept.

В развитие gap-парадигмы, описывающей устойчивость лесных сообществ как динамический процесс (баланс между образованием «окон» или «прорывов» лесного полога и восстановлением его элементов в ходе популяционной жизни деревьев и кустарников), а
их пространственную структуру — как совокупность нарушений, находящихся на разных стадиях зарастания, реконструируется роль дятловых птиц в этой динамике, в зависимости от видов лесных биомов и степени их нарушенности

Invasive species threaten global biodiversity, but multiple invasions make predicting the impacts difficult because of potential synergistic effects. We examined the impact of introduced beaver Castor canadensis, brook trout Salvelinus fontinalis, and rainbow trout Oncorhynchus mykiss on native stream fishes in the Cape Horn Biosphere Reserve, Chile. The combined effects of introduced species on the structure of the native freshwater fish community were quantified by electrofishing 28 stream reaches within four riparian habitat types (forest, grassland, shrubland, and beaver-affected habitat) in 23 watersheds and by measuring related habitat variables (water velocity, substrate type, depth, and the percentage of pools). Three native stream fish species (puye Galaxias maculatus [also known as inanga], Aplochiton taeniatus, and A. zebra) were found along with brook trout and rainbow trout, but puye was the only native species that was common and widespread. The reaches affected by beaver impoundments had significantly higher puye densities than all other reaches in this study. These results are comparable to those reported for other streams in southern Chile. The presence of trout reduced the abundance of puye, but only in beaver-affected areas; all three natural riparian habitat types had uniformly low puye abundance and were unaffected by the presence or absence of trout. The data suggest that one invasive species, the beaver, enhanced puye habitat and thereby increased the abundance of that species, which, in turn, helped moderate the negative impacts of invasive trout.

La ingenieria ambiental es una carrera nueva en el Peru, trata de la gestion de los ecosistemas. Existen en la naturaleza, ingenieros no humanos, organismos capaces de mantener, crear o modificar el paisaje y por consiguiente el ecosistema donde esten. Hay varios ejemplos de plantas y animales que son ingenieros de ecosistemas. Las aves ocupan un rol muy importante en los ecosistemas, pues proveen de varios servicios ambientales; tales como dispersión de semillas, polinización, remoción de carcasas, fertilización de suelos, construcción de hábitats entre otros. La remoción de especies claves de aves ha causado cambios sustanciales en ecosistemas en distintos lugares del mundo. En el Peru, hay varios grupos de aves que proveen estos servicios ambientales; los pajaros carpinteros, las aves guaneras, los pajaros frugivoros, los insectívoros, los colibries y los pinchaflores. Estos sultimos, son aves del genero Diglossa conocidos como ladrones de nectar, supuestamente perjudiciales para las plantas con flores. Sin embargo, en mis investigaciones en el bosque de Unchog he visto que son facilitadores para otras especies de colibries de pico corto que no podrian alcanzar el nectar de flores largas de no ser por su actividad de agujerear las flores. A parecer, no afectan tampoco la producción y concentración de nectar.

Communities are shaped by the activity of ecosystem engineers, which modify their environment to their benefit and that of subordinate species within their functional domain. Communities are defined as embedded assemblages of interactions, from cells to landscapes. They are threatened by present-day global changes which trigger the invasive nature of ecological engineers, with cascading effects. This perspective paper starts with a definition of ecosystem engineers and functional domains in the frame of developments in community ecology. Then I show that the concepts of ecosystem engineer and functional domain explain (i) most of the observed cases of community boundaries, and (ii) the passage from small-scale interactions among individuals to community-wide processes of dynamics and stability. I will further show that ecological engineering exists at various scales, from viruses to landscapes, functional domains being embedded in a flexible manner. At last, I will show that threats posed by global changes to communities are mainly mediated by their negative or positive effects on ecosystem engineers.

We present a general framework for characterizing the ecological and societal consequences of biodiversity loss and applying it to the global avifauna. To investigate the potential ecological consequences of avian declines, we developed comprehensive databases of the status and functional roles of birds and a stochastic model for forecasting change. Overall, 21% of bird species are currently extinction-prone and 6.5% are functionally extinct, contributing negligibly to ecosystem processes. We show that a quarter or more of frugivorous and omnivorous species and one-third or more of herbivorous, piscivorous, and scavenger species are extinction-prone.
Furthermore, our projections indicate that by 2100, 6–14%
of all bird species will be extinct, and 7–25% (28–56% on oceanic islands) will be functionally extinct. Important ecosystem processes, particularly decomposition, pollination, and seed dispersal, will likely decline as a result.

Although the ecosystem engineering concept is well established in ecology, cases of joint engineering by multiple species at large scales remain rare. Here, we combine observational studies and exclosure experiments to investigate how co-occurring greater flamingos Phoenicopterus roseus and fiddler crabs Uca tangeri promote their own and each other’s food availability by creating a spatially complex mosaic of depressions (bowls, gullies) and hummocks (plateaus, mounds) in the intertidal zone. This results in a mosaic of microhabitats with different tidal inundation regimes. These microhabitats are spatially organized with labyrinth-like patterns in the high intertidal zone and spotted patterns in the lower intertidal, both of which likely arise from biophysical interactions between these organisms and hydrodynamic forces. We show that the resulting spatial complexity is vital for biofilm production. The depression microhabitats were wetter and richer in organic matter and biofilms compared with hummocks. Excluding flamingos and crabs resulted in an increase in biofilm biomass over the shorter term (six months), but a decrease over the longer term (after one year). Moreover, our results strongly suggest that these biogeomorphological microhabitats in the mosaics were maintained by the feeding activities of flamingos and to a lesser extent crabs. During a period of flamingo exclusion, all the spotted patterns filled up with sediment, while the exclusion of crabs led to gradual sediment accumulation in the labyrinth-like patterns. Collectively, these findings provide empirical evidence for large-scale joint promotion of food availability by multiple taxa in a marine ecosystem

Background: Studies on plant–plant interactions in alpine ecosystems show a strong bias for temperate vs. tropical latitudes
and pay limited attention to the implications of biophysical heterogeneity beyond the local plant scale.
Aims: To evaluate the effects of a dominant shrub (Hypericum laricifolium) on community organisation, integrating multiple
scales of analysis, in a high Andean páramo in Venezuela.
Methods: We compared plant cover, species richness and Shannon diversity between plots placed under the shrub and
outside (plant scale); quantified the spatial relations of Hypericum with its conspecifics, heterospecifics and rocks at different
radial distances, using covariance functions (patch scale); analysed the effects of Hypericum shrubs on total species richness
in the community (site scale); and evaluated the consistency of our results among four sites within the same region
(between-site scale).
Results: Average species richness, Shannon diversity, and the abundance of common forbs and conspecific shrubs were
consistently higher inside the Hypericum shrub, while the exotic Rumex acetosella was more abundant in open areas.
However, the aggregated spatial distribution of conspecifics and other species extended beyond the local plant scale and
there were no clear effects of Hypericum shrubs on community-level species richness.
Conclusions: Shrubs can function as foundation species in tropical alpine environments, modifying local community
structure and alpha diversity, but not necessarily the species richness of the overall community. Our results stress the
need of analysing multiple spatial scales to interpret the role of plant–plant interactions (facilitation/competition) in
heterogeneous alpine ecosystems.

Plants serve as both basal resources and ecosystem engineers, so plant invasion may exert trophic influences on consumers both via bottom-up processes and by altering the environmental context in which trophic interactions occur. To determine how these mechanisms affect a native predator we used a mark-recapture study in eight pairs of 58m2 field enclosures to measure the influence of Japanese stilt-grass invasion on 3200 recently metamorphosed American toads. Toad survivorship was lower in invaded habitats despite abiotic effects that favor amphibians. Prey densities were also lower in invaded habitats, but growth was unaffected. Frequent spider predation events in invaded habitats led us to use factorial field cage manipulations of stilt-grass and lycosid spiders to determine if invasion increases predation rates. Spiders persisted at higher densities in the presence of stilt-grass, and toad survival was lowest in cages with both grass and spiders. Invasion alone did not significantly reduce toad survival. Our results demonstrate that despite prey reductions and abiotic effects, it is increased spider persistence that reduces toad survival in invaded habitats. Invasion therefore affects resident forest floor consumers by modifying trophic interactions between native species, causing structurally mediated reductions in intraguild predation rates among spiders, with cascading implications for toad survival.

Nonnative species that form novel habitats strongly affect ecosystem processes. The effects of these ecosystem engineers can be both positive and negative but the mechanisms behind their effects are not well described. In this study we determined the relative importance of three main mechanisms by which invasive ecosystem engineers can facilitate native fauna. The engineer may provide new physical structure that reduces harsh abiotic conditions or gives refuge from predation (both engineering mechanisms), or provide a new profitable food resource (a trophic mechanism). The invasive seaweed Gracilaria vermiculophylla is a novel addition to estuarine intertidal mudflats of the southeastern United States. The epifaunal amphipod Gammarus mucronatus is up to 100 times more abundant on Gracilaria-invaded mudflats compared to uninvaded mudflats. Feeding assays, a survivorship experiment and stable isotope analysis demonstrated that Gammarus consumes little Gracilaria and cannot survive on Gracilaria alone. However, the structural engineering effects of Gracilaria greatly enhanced the survivorship of Gammarus in the presence of predators during high tide and when exposed to harsh abiotic conditions during low tide. Our results demonstrate that invasive ecosystem engineers can dramatically affect the distribution and abundance of native species by providing a novel protective structure.

Read More: http://www.esajournals.org/doi/abs/10.1890/14-0127.1

The disappearance of the soft-bodied Ediacara biota at the Ediacaran–Cambrian boundary potentially represents the earliest mass extinction of complex life, although the precise driver(s) of this extinction remain unresolved. The ‘biotic replacement’ model proposes that an evolutionary radiation of metazoan ecosystem engineers in the latest Ediacaran profoundly altered marine palaeoenvironments, resulting in the extinction of Ediacara biota and setting the stage for the subsequent Cambrian Explosion. However, metazoan ecosystem engineering across the Ediacaran–Cambrian transition has yet to be quantified. Here, we test this key tenet of the biotic replacement model by characterizing the intensity of metazoan bioturbation and ecosystem engineering in trace fossil
assemblages throughout the latest Ediacaran Nama Group in southern Namibia. The results illustrate a dramatic increase in both bioturbation and ecosystem engineering intensity in the latest Ediacaran, prior to the Cambrian boundary. Moreover, our analyses demonstrate that the highest-impact ecosystem engineering behaviours were present well before the onset of the Cambrian. These data provide the first support for a fundamental prediction of the biotic replacement model, and evidence for a direct link between the early evolution of ecosystem engineering and the extinction of the Ediacara biota.

New knowledge on soil structure highlights its importance for hydrology and soil organic matter (SOM) stabilization, which however remains neglected in many wide used models. We present here a new model, KEYLINK, in which soil structure is integrated with the existing concepts on SOM pools, and elements from food web models, that is, those from direct trophic interactions among soil organisms. KEYLINK is, therefore, an attempt to integrate soil functional diversity and food webs in predictions of soil carbon (C) and soil water balances. We present a selection of equations that can be used for most models as well as basic parameter intervals, for example, key pools, functional groups’ biomasses and growth rates. Parameter distributions can be determined with Bayesian calibration, and here an example is presented for food web growth rate parameters for a pine forest in Belgium. We show how these added equations can improve the functioning of the model in describing known phenomena. Fo...