9,358 research outputs found
The shape of ecological networks
We study the statistics of ecosystems with a variable number of co-evolving
species. The species interact in two ways: by prey-predator relationships and
by direct competition with similar kinds. The interaction coefficients change
slowly through successful adaptations and speciations. We treat them as
quenched random variables. These interactions determine long-term topological
features of the species network, which are found to agree with those of
biological systems.Comment: 4 pages, 2 figure
Interplay of spatial dynamics and local adaptation shapes species lifetime distributions and species-area relationships
The distributions of species lifetimes and species in space are related,
since species with good local survival chances have more time to colonize new
habitats and species inhabiting large areas have higher chances to survive
local disturbances. Yet, both distributions have been discussed in mostly
separate communities. Here, we study both patterns simultaneously using a
spatially explicit, evolutionary community assembly approach. We present and
investigate a metacommunity model, consisting of a grid of patches, where each
patch contains a local food web. Species survival depends on predation and
competition interactions, which in turn depend on species body masses as the
key traits. The system evolves due to the migration of species to neighboring
patches, the addition of new species as modifications of existing species, and
local extinction events. The structure of each local food web thus emerges in a
self-organized manner as the highly non-trivial outcome of the relative time
scales of these processes. Our model generates a large variety of complex,
multi-trophic networks and therefore serves as a powerful tool to investigate
ecosystems on long temporal and large spatial scales. We find that the observed
lifetime distributions and species-area relations resemble power laws over
appropriately chosen parameter ranges and thus agree qualitatively with
empirical findings. Moreover, we observe strong finite-size effects, and a
dependence of the relationships on the trophic level of the species. By
comparing our results to simple neutral models found in the literature, we
identify the features that are responsible for the values of the exponents.Comment: Theor Ecol (2019
Species assembly in model ecosystems, II: Results of the assembly process
In the companion paper of this set (Capitan and Cuesta, 2010) we have
developed a full analytical treatment of the model of species assembly
introduced in Capitan et al. (2009). This model is based on the construction of
an assembly graph containing all viable configurations of the community, and
the definition of a Markov chain whose transitions are the transformations of
communities by new species invasions. In the present paper we provide an
exhaustive numerical analysis of the model, describing the average time to the
recurrent state, the statistics of avalanches, and the dependence of the
results on the amount of available resource. Our results are based on the fact
that the Markov chain provides an asymptotic probability distribution for the
recurrent states, which can be used to obtain averages of observables as well
as the time variation of these magnitudes during succession, in an exact
manner. Since the absorption times into the recurrent set are found to be
comparable to the size of the system, the end state is quickly reached (in
units of the invasion time). Thus, the final ecosystem can be regarded as a
fluctuating complex system where species are continually replaced by newcomers
without ever leaving the set of recurrent patterns. The assembly graph is
dominated by pathways in which most invasions are accepted, triggering small
extinction avalanches. Through the assembly process, communities become less
resilient (e.g., have a higher return time to equilibrium) but become more
robust in terms of resistance against new invasions.Comment: 14 pages, 13 figures. Revised versio
Species assembly in model ecosystems, I: Analysis of the population model and the invasion dynamics
Recently we have introduced a simplified model of ecosystem assembly (Capitan
et al., 2009) for which we are able to map out all assembly pathways generated
by external invasions in an exact manner. In this paper we provide a deeper
analysis of the model, obtaining analytical results and introducing some
approximations which allow us to reconstruct the results of our previous work.
In particular, we show that the population dynamics equations of a very general
class of trophic-level structured food-web have an unique interior equilibrium
point which is globally stable. We show analytically that communities found as
end states of the assembly process are pyramidal and we find that the
equilibrium abundance of any species at any trophic level is approximately
inversely proportional to the number of species in that level. We also find
that the per capita growth rate of a top predator invading a resident community
is key to understand the appearance of complex end states reported in our
previous work. The sign of these rates allows us to separate regions in the
space of parameters where the end state is either a single community or a
complex set containing more than one community. We have also built up
analytical approximations to the time evolution of species abundances that
allow us to determine, with high accuracy, the sequence of extinctions that an
invasion may cause. Finally we apply this analysis to obtain the communities in
the end states. To test the accuracy of the transition probability matrix
generated by this analytical procedure for the end states, we have compared
averages over those sets with those obtained from the graph derived by
numerical integration of the Lotka-Volterra equations. The agreement is
excellent.Comment: 16 pages, 8 figures. Revised versio
On the interplay of speciation and dispersal: An evolutionary food web model in space
We introduce an evolutionary metacommunity of multitrophic food webs on
several habitats coupled by migration. In contrast to previous studies that
focus either on evolutionary or on spatial aspects, we include both and
investigate the interplay between them. Locally, the species emerge, interact
and go extinct according to the rules of the well-known evolutionary food web
model proposed by Loeuille and Loreau in 2005. Additionally, species are able
to migrate between the habitats. With random migration, we are able to
reproduce common trends in diversity-dispersal relationships: Regional
diversity decreases with increasing migration rates, whereas local diversity
can increase in case of a low level of dispersal. Moreover, we find that the
total biomasses in the different patches become similar even when species
composition remains different. With adaptive migration, we observe species
compositions that differ considerably between patches and contain species that
are descendant from ancestors on both patches. This result indicates that the
combination of spatial aspects and evolutionary processes affects the structure
of food webs in different ways than each of them alone.Comment: under review at JT
Mutual information in the Tangled Nature Model
We consider the concept of mutual information in ecological networks, and use
this idea to analyse the Tangled Nature model of co-evolution. We show that
this measure of correlation has two distinct behaviours depending on how we
define the network in question: if we consider only the network of viable
species this measure increases, whereas for the whole system it decreases. It
is suggested that these are complimentary behaviours that show how ecosystems
can become both more stable and better adapted.Comment: 7 pages, 5 figures. To appear in Ecological Modellin
Ecological criteria for evaluation candidate sites for marine reserves
Several schemes have been developed to help select the locations of marine reserves. All of them combine social, economic, and biological criteria, and few offer any guidance as to how to prioritize among the criteria identified. This can imply that the relative weights given to different criteria are unimportant. Where two sites are of equal value ecologically, then socioeconomic criteria should dominate the choice of which should be protected. However, in many cases, socioeconomic criteria are given equal or greater weight than ecological considerations in the choice of sites. This can lead to selection of reserves with little biological value that fail to meet many of the desired objectives. To avoid such a possibility, we develop a series of criteria that allow preliminary evaluation of candidate sites according to their relative biological values in advance of the application of socioeconomic criteria. We include criteria that, while not strictly biological, have a strong influence on the species present or ecological processes. Our scheme enables sites to be assessed according to their biodiversity, the processes which underpin that diversity, and the processes that support fisheries and provide a spectrum of other services important to people. Criteria that capture biodiversity values include biogeographic representation, habitat representation and heterogeneity, and presence of species or populations of special interest (e.g., threatened species). Criteria that capture sustainability of biodiversity and fishery values include the size of reserves necessary to protect viable habitats, presence of exploitable species, vulnerable life stages, connectivity among reserves, links among ecosystems, and provision of ecosystem services to people. Criteria measuring human and natural threats enable candidate sites to be eliminated from consideration if risks are too great, but also help prioritize among sites where threats can be mitigated by protection. While our criteria can be applied to the design of reserve networks, they also enable choice of single reserves to be made in the context of the attributes of existing protected areas. The overall goal of our scheme is to promote the development of reserve networks that will maintain biodiversity and ecosystem functioning at large scales. The values of ecosystem goods and services for people ultimately depend on meeting this objective
A bio-economic model for the ecosystem-based management of the coastal fishery in French Guiana
This paper offers a theoretical and empirical modeling for ecosystem-based fishery management (EBFM). A multi-species and multi-fleets model integrating Lokta-Volterra trophic dynamics and profit functions is developed for the coastal fishery of French Guiana. This small-case fishery constitutes a challenging example with high fish biodiversity, several non selective fleets and a potentially increasing local food demand due to demographic pressure. The dynamic model is calibrated with thirteen species and four fleets using catch and effort data on a monthly basis from 2006 to 2009. Several contrasting fishing scenarios including status quo, total closure, economic and viable strategies are simulated and compared from both biodiversity preservation and socio-economic performance viewpoints. We show that fishing outputs including food supply and profitability of fleets can be sustained although a significant loss of biodiversity cannot be avoided.Small-scale fishery, biodiversity, sustainability, profitability, food security, multi-species, multi-fleets
- …