2,061 research outputs found
Modelling Emergent Patterns of Dynamic Desert Ecosystems
In many desert ecosystems vegetation is both patchy and dynamic: vegetated areas are interspersed with patches of bare ground, and both the positioning and the species composition of the vegetated areas exhibit change through time. These characteristics lead to the emergence of multi-scale patterns in vegetation that arise from complex relationships between plants, soils and transport processes. Previous attempts to probe the causes of spatial complexity and predict responses of desert ecosystems tend to be limited in their focus: models of dynamics have been developed with no consideration of the inherent patchiness in the vegetation, or else models have been developed to generate patterns with no consideration of the dynamics. Here we develop a general modelling framework for the analysis of ecosystem change in deserts that is rooted in the
concept of connectivity and is derived from a detailed process-based understanding. We explicitly consider spatial interactions among multiple vegetation types and multiple resources, and our model is formulated to predict responses to a variety of endogenous and exogenous disturbances. The model is implemented in the deserts of the American Southwest both to test hypotheses of the causes of the invasion of woody shrubs, and to test its ability to reproduce
16 observed spatial differences in response to drought in the twentieth century. The model’s performance leads us to argue that vertical and lateral connectivity are key emergent properties of the ecosystem, which both control its behaviour and provide indicators of its state. If this argument is shown to be compatible with field observations, the model presented here will provide a more certain approach towards preventing further degradation of semi-arid grasslands.
http://www.esajournals.org/doi/pdf/10.1890/12-1253.
Plant clonal morphologies and spatial patterns as self-organized responses to resource-limited environments
We propose here to interpret and model peculiar plant morphologies (cushions,
tussocks) observed in the Andean altiplano as localized structures. Such
structures resulting in a patchy, aperiodic aspect of the vegetation cover are
hypothesized to self-organize thanks to the interplay between facilitation and
competition processes occurring at the scale of basic plant components
biologically referred to as 'ramets'. (Ramets are often of clonal origin.) To
verify this interpretation, we applied a simple, fairly generic model (one
integro-differential equation) emphasizing via Gaussian kernels non-local
facilitative and competitive feedbacks of the vegetation biomass density on its
own dynamics. We show that under realistic assumptions and parameter values
relating to ramet scale, the model can reproduce some macroscopic features of
the observed systems of patches and predict values for the inter-patch distance
that match the distances encountered in the reference area (Sajama National
Park in Bolivia). Prediction of the model can be confronted in the future to
data on vegetation patterns along environmental gradients as to anticipate the
possible effect of global change on those vegetation systems experiencing
constraining environmental conditions.Comment: 14 pages, 6figure
Extended patchy ecosystems may increase their total biomass through self-replication
Patches of vegetation consist of dense clusters of shrubs, grass, or trees,
often found to be circular characteristic size, defined by the properties of
the vegetation and terrain. Therefore, vegetation patches can be interpreted as
localized structures. Previous findings have shown that such localized
structures can self-replicate in a binary fashion, where a single vegetation
patch elongates and divides into two new patches. Here, we extend these
previous results by considering the more general case, where the plants
interact non-locally, this extension adds an extra level of complexity and
shrinks the gap between the model and real ecosystems, where it is known that
the plant-to-plant competition through roots and above-ground facilitating
interactions have non-local effects, i.e. they extend further away than the
nearest neighbor distance. Through numerical simulations, we show that for a
moderate level of aridity, a transition from a single patch to periodic pattern
occurs. Moreover, for large values of the hydric stress, we predict an opposing
route to the formation of periodic patterns, where a homogeneous cover of
vegetation may decay to spot-like patterns. The evolution of the biomass of
vegetation patches can be used as an indicator of the state of an ecosystem,
this allows to distinguish if a system is in a self-replicating or decaying
dynamics. In an attempt to relate the theoretical predictions to real
ecosystems, we analyze landscapes in Zambia and Mozambique, where vegetation
forms patches of tens of meters in diameter. We show that the properties of the
patches together with their spatial distributions are consistent with the
self-organization hypothesis. We argue that the characteristics of the observed
landscapes may be a consequence of patch self-replication, however, detailed
field and temporal data is fundamental to assess the real state of the
ecosystems.Comment: 38 pages, 12 figures, 1 tabl
Assessing Simulations of Imperial Dynamics and Conflict in the Ancient World
The development of models to capture large-scale dynamics in human history is
one of the core contributions of cliodynamics. Most often, these models are
assessed by their predictive capability on some macro-scale and aggregated
measure and compared to manually curated historical data. In this report, we
consider the model from Turchin et al. (2013), where the evaluation is done on
the prediction of "imperial density": the relative frequency with which a
geographical area belonged to large-scale polities over a certain time window.
We implement the model and release both code and data for reproducibility. We
then assess its behaviour against three historical data sets: the relative size
of simulated polities vs historical ones; the spatial correlation of simulated
imperial density with historical population density; the spatial correlation of
simulated conflict vs historical conflict. At the global level, we show good
agreement with population density (), and some agreement with
historical conflict in Europe (). The model instead fails to
reproduce the historical shape of individual polities. Finally, we tweak the
model to behave greedily by having polities preferentially attacking weaker
neighbours. Results significantly degrade, suggesting that random attacks are a
key trait of the original model. We conclude by proposing a way forward by
matching the probabilistic imperial strength from simulations to inferred
networked communities from real settlement data
Diversity and Distribution Patterns of Geometrid Moths (Geometridae, Lepidoptera) in Mongolia
Geometrids are a species-rich group of moths that serve as reliable indicators for environmental changes. Little is known about the Mongolian moth fauna, and there is no comprehensive review of species richness, diversity, and distribution patterns of geometrid moths in the country. Our study aims to review the existing knowledge on geometrid moths in Mongolia. We compiled geometrid moth records from published scientific papers, our own research, and from the Global Biodiversity Information Facility (GBIF) to produce a checklist of geometrid moths of Mongolia. Additionally, we analyzed spatial patterns, species richness, and diversity of geometrid moths within 14 ecoregions of Mongolia and evaluated environmental variables for their distribution. In total, we compiled 1973-point records of 388 geometrid species. The most species-rich ecoregion in Mongolia was Daurian Forest Steppe with 142 species. Annual precipitation and maximum temperature of the warmest month were the most important environmental variables that correlated with NMDS axes in an analysis of geometrid assemblages of different ecoregions in Mongolia
Fairy circle landscapes under the sea
Short-scale interactions yield large-scale vegetation patterns that, in turn,
shape ecosystem function across landscapes. Fairy circles, which are circular
patches bare of vegetation within otherwise continuous landscapes, are
characteristic features of semiarid grasslands. We report the occurrence of
submarine fairy circle seascapes in seagrass meadows and propose a simple model
that reproduces the diversity of seascapes observed in these ecosystems as
emerging from plant interactions within the meadow. These seascapes include two
extreme cases, a continuous meadow and a bare landscape, along with
intermediate states that range from the occurrence of persistent but isolated
fairy circles, or solitons, to seascapes with multiple fairy circles, banded
vegetation, and "leopard skin" patterns consisting of bare seascapes patterns
consisting of bare seascapes dotted with plant patches. The model predicts that
these intermediate seascapes extending across kilometers emerge as a
consequence of local demographic imbalances along with facilitative and
competitive interactions among the plants with a characteristic spatial scale
of 20 to 30 m, consistent with known drivers of seagrass performance. The
model, which can be extended to clonal growth plants in other landscapes
showing fairy rings, reveals that the different seascapes observed hold
diagnostic power as to the proximity of seagrass meadows to extinction points
that can be used to identify ecosystems at risks
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