Stochasticity-induced stabilization weakens in diverse communities.

2021 ◽  
Author(s):  
Jayant Pande ◽  
Nadav Shnerb
Keyword(s):  
Species Richness ◽  
Temporal Variations ◽  
Environmental Stochasticity ◽  
Storage Effect ◽  
Demographic Rates ◽  
Diverse Communities ◽  
Environmental Variations ◽  
Autocorrelation Time ◽  
Coexistence State ◽  
Competing Populations

Environmental stochasticity and the temporal variations of demographic rates associated with it are ubiquitous in nature. The ability of these fluctuations to stabilize a coexistence state of competing populations (sometimes known as the storage effect) is a counterintuitive feature that has aroused much interest. Here we consider the performance of environmental stochasticity as a stabilizer in diverse communities. We show that the effect of stochasticity is buffered because of the differential response of populations to environmental variations, and its stabilizing effect disappears as the number of populations increases. Of particular importance is the ratio between the autocorrelation time of the environment and the generation time. Species richness grows with stochasticity only when this ratio is smaller than the inverse of the fundamental biodiversity parameter. When stochasticity impedes coexistence and lowers the species richness, the ratio between the strength of environmental variations and the speciation (or migration) rate governs its effect.

scholarly journals Species coexistence and temporal environmental fluctuations: a quantitative comparison between stochastic and seasonal variations.

2021 ◽  
Author(s):  
Immanuel Meyer ◽  
bnaya Steinmetz ◽  
Nadav Shnerb
Keyword(s):  
Species Coexistence ◽  
Temporal Variations ◽  
Analytic Solutions ◽  
Environmental Stochasticity ◽  
Community Size ◽  
Periodic Environment ◽  
Stochastic Fluctuations ◽  
Time To Extinction ◽  
Environmental Variations ◽  
Mean Time

Temporal environmental variations may promote diversity in communities of competing populations. Here we compare the effect of environmental stochasticity with the effect of periodic (e.g., seasonal) cycles, using analytic solutions and individual-based Monte-Carlo simulations. Even when stochasticity facilitates coexistence it still allows for rare sequences of bad years that may drive a population to extinction, therefore the stabilizing effect of periodic variations is stronger. Correspondingly, the mean time to extinction grows exponentially with community size in periodic environment and switch to power-law dependence under stochastic fluctuations. On the other hand, the number of temporal niches in periodic environment is typically lower, so as diversity increases stochastic temporal variations may support higher species richness.

Community characteristics of forest understory birds along an elevational gradient in the Horn of Africa: A multi-year baseline

The Condor ◽  
2021 ◽  
Author(s):  
Kyle D Kittelberger ◽  
Montague H C Neate-Clegg ◽  
Evan R Buechley ◽  
Çağan Hakkı Şekercioğlu
Keyword(s):  
Species Richness ◽  
Species Turnover ◽  
Survival Rates ◽  
Elevational Gradient ◽  
Forest Understory ◽  
Bird Abundance ◽  
Tropical Mountains ◽  
Demographic Rates ◽  
Understory Birds ◽  
Over Time

Abstract Tropical mountains are global hotspots for birdlife. However, there is a dearth of baseline avifaunal data along elevational gradients, particularly in Africa, limiting our ability to observe and assess changes over time in tropical montane avian communities. In this study, we undertook a multi-year assessment of understory birds along a 1,750 m elevational gradient (1,430–3,186 m) in an Afrotropical moist evergreen montane forest within Ethiopia’s Bale Mountains. Analyzing 6 years of systematic bird-banding data from 5 sites, we describe the patterns of species richness, abundance, community composition, and demographic rates over space and time. We found bimodal patterns in observed and estimated species richness across the elevational gradient (peaking at 1,430 and 2,388 m), although no sites reached asymptotic species richness throughout the study. Species turnover was high across the gradient, though forested sites at mid-elevations resembled each other in species composition. We found significant variation across sites in bird abundance in some of the dietary and habitat guilds. However, we did not find any significant trends in species richness or guild abundances over time. For the majority of analyzed species, capture rates did not change over time and there were no changes in species’ mean elevations. Population growth rates, recruitment rates, and apparent survival rates averaged 1.02, 0.52, and 0.51 respectively, and there were no elevational patterns in demographic rates. This study establishes a multi-year baseline for Afrotropical birds along an elevational gradient in an under-studied international biodiversity hotspot. These data will be critical in assessing the long-term responses of tropical montane birdlife to climate change and habitat degradation.

scholarly journals First reports of short-term temporal variations in crustacean species richness in north Patagonian coastal temporary pools

Nauplius ◽  
2021 ◽  
Vol 29 ◽  
Author(s):  
Patricio De los Ríos-Escalante ◽  
Francisco Encina-Montoya ◽  
Eriko Carreño ◽  
Francisco Correa-Araneda ◽  
Carlos Esse
Keyword(s):  
Species Richness ◽  
Temporal Variations ◽  
Temporary Pools ◽  
Short Term ◽  
Crustacean Species

scholarly journals Responses of the molluscan fauna to environmental variations in a Halodule wrightii Ascherson ecosystem from Northeastern Brazil

2013 ◽  
Vol 85 (4) ◽  
pp. 1397-1410 ◽  
Author(s):  
KCRISHNA V.S. BARROS ◽  
CRISTINA A. ROCHA-BARREIRA
Keyword(s):  
Seasonal Changes ◽  
Common Species ◽  
Temporal Variations ◽  
Northeastern Brazil ◽  
Halodule Wrightii ◽  
Hypnea Musciformis ◽  
Spatial And Temporal Distributions ◽  
Environmental Variations ◽  
Vertical Variations ◽  
Molluscan Fauna

ABSTRACT This study observed the spatial and temporal distributions of molluscs in a Halodule wrightii meadow, verifying if they respond satisfactorily to seasonal changes in this seagrass ecosystem. Twenty-four species were identified. Chitons were rare, bivalves had greater number of species (11), followed by gastropods (9) which were also the most abundant class (73%). All classes were more abundant in the belowground. The most common species was Tricolia affinis, especially in aboveground. The occurrence of some species in both strata or out of the expected stratum may have been influenced by shallow layer of the sediment considered in this study, hydrodynamic, and low biomass of the studied meadow. According to univariate and multivariate analyses, despite of molluscan descriptors had been related to variables associated with rainfall, the seagrasses had an important role on the seasonal and vertical variations of the molluscan fauna. The biomass of the epiphyte Hypnea musciformis was correlated to temporal variations of the species from aboveground, indicating its secondary role for this community. The molluscs were sensible to environmental variations, and also reflected seasonal changes of the seagrass, showing that damages on these meadows reflect even at lower levels of the marine food web.

Grasshopper (Orthoptera: Acrididea) assemblages in forests and savanna areas in Center, West and South-west regions of Cameroon

2019 ◽  
Vol 12 (1) ◽  
pp. 17-32
Author(s):  
ALAIN CHRISTEL WANDJI ◽  
SÉVILOR KEKEUNOU ◽  
MARCELLE MBADJOUN NZIKE ◽  
ALAIN SIMEU NOUTCHOUM ◽  
ABRAHAM FOMENA
Keyword(s):  
Species Richness ◽  
Vegetation Type ◽  
Forest Degradation ◽  
Dissimilarity Index ◽  
Grasshopper Species ◽  
Crop Fields ◽  
Environmental Variations ◽  
Capture Method ◽  
First Time

Forest degradation due to human activities is a major threat to the long-term persistence of many species. It affects species richness, abundance and can lead to the extinction of some species. The present work aimed at identifying the effect of environmental variations on the species richness and composition of grasshoppers in three regions Cameroon. In each region, four vegetations (forests, agroforests, fallows and crop fields) were investigated using sweep nets and pitfalls trapping for specimens’ capture from February 2016 to February 2018. From this study, 92 grasshoppers species belonging to 3 families, 13 subfamilies and 70 genera were collected. The Acrididae was the most diverse family with 77 species. The Catantopinae was the richest subfamily (22 species), while the Pterotiltus was the richest genus with 7 species. Overall, the average sample success was 92.49%. We found that the species richness was strongly influenced by the study site (region), the vegetation type, and the capture method. The dissimilarity index revealed that the grasshopper communities of West and Center region were similar to each other, like those of fallows and crop fields.  Twenty-four species of grasshopper could be reported for the first time in Cameroon. This study updates the database on the grasshopper fauna of Cameroon and brings to 238 the number of grasshopper species known in Cameroon. Key words: Grasshoppers, species richness, forests, agroforests, fallows, crop fields

scholarly journals Saturating effects of species diversity on life-history evolution in bacteria

2015 ◽  
Vol 282 (1815) ◽  
pp. 20151794 ◽  
Author(s):  
Francesca Fiegna ◽  
Thomas Scheuerl ◽  
Alejandra Moreno-Letelier ◽  
Thomas Bell ◽  
Timothy G. Barraclough
Keyword(s):  
Life History ◽  
Species Richness ◽  
Species Interactions ◽  
Evolutionary Dynamics ◽  
Life History Evolution ◽  
Relative Strength ◽  
Recent Theory ◽  
Mechanistic Models ◽  
As Species ◽  
Diverse Communities

Species interactions can play a major role in shaping evolution in new environments. In theory, species interactions can either stimulate evolution by promoting coevolution or inhibit evolution by constraining ecological opportunity. The relative strength of these effects should vary as species richness increases, and yet there has been little evidence for evolution of component species in communities. We evolved bacterial microcosms containing between 1 and 12 species in three different environments. Growth rates and yields of isolates that evolved in communities were lower than those that evolved in monocultures, consistent with recent theory that competition constrains species to specialize on narrower sets of resources. This effect saturated or reversed at higher levels of richness, consistent with theory that directional effects of species interactions should weaken in more diverse communities. Species varied considerably, however, in their responses to both environment and richness levels. Mechanistic models and experiments are now needed to understand and predict joint evolutionary dynamics of species in diverse communities.

scholarly journals Short term changes in zooplankton community during the summer-autumn transition in the open NW Mediterranean Sea: species composition, abundance and diversity

2008 ◽  
Vol 5 (6) ◽  
pp. 1765-1782 ◽  
Author(s):  
V. Raybaud ◽  
P. Nival ◽  
L. Mousseau ◽  
A. Gubanova ◽  
D. Altukhov ◽  
...  
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Zooplankton Community ◽  
Mesh Size ◽  
Temporal Variations ◽  
Water Masses ◽  
Short Term ◽  
Low Salinity ◽  
Low Salinity Water ◽  
Salinity Water

Abstract. Short term changes in zooplankton community were investigated at a fixed station in offshore waters of the Ligurian Sea (DYNAPROC 2 cruise, September–October 2004). Mesozooplankton were sampled with vertical WP-II hauls (200 μm mesh-size) and large mesozooplankton, macrozooplankton and micronekton with a BIONESS multinet sampler (500 μm mesh-size). Temporal variations of total biomass, species composition and abundance of major taxa were studied. Intrusions of low salinity water masses were observed two times during the cruise. The first one, which was the most intense, was associated with changes in zooplankton community composition. Among copepods, the abundance of Calocalanus, Euchaeta, Heterorhabdus, Mesocalanus, Nannocalanus, Neocalanus, Pleuromammaand also calanoid copepodites increased markedly. Among non-copepod taxa, only small ostracods abundance increased. After this low salinity event, abundance of all taxa nearly returned to their initial values. The influence of salinity on each zooplankton taxon was confirmed by a statistical analysis (Perry's method). The Shannon diversity index, Pielou evenness and species richness were used to describe temporal variations of large copepod (>500 μm) diversity. The Shannon index and Pielou evenness decreased at the beginning of the low salinity water intrusions, but not species richness. We suggest that low salinity water masses contained its own zooplankton community and passed through the sampling area, thus causing a replacement of the zooplankton population.

scholarly journals The effect of environmental stochasticity on species richness in neutral communities

2016 ◽  
Vol 409 ◽  
pp. 155-164 ◽  
Author(s):  
Matan Danino ◽  
Nadav M. Shnerb ◽  
Sandro Azaele ◽  
William E. Kunin ◽  
David A. Kessler
Keyword(s):  
Species Richness ◽  
Environmental Stochasticity

scholarly journals Stochasticity-induced stabilization in ecology and evolution

2019 ◽  
Author(s):  
Antony Dean ◽  
Nadav M. Shnerb
Keyword(s):  
Population Genetics ◽  
Species Richness ◽  
Diffusion Approximation ◽  
Generation Time ◽  
Overlapping Generations ◽  
Storage Effect ◽  
Asymmetric Competition ◽  
Bet Hedging ◽  
Qualitative And Quantitative ◽  
Hedging Strategies

AbstractThe ability of random environmental variation to stabilize competitor coexistence was pointed out long ago and, in recent years, has received considerable attention. Here we suggest a novel and generic synthesis of stochasticity-induced stabilization (SIS) phenomena. The storage effect in the lottery model, together with other well-known examples drawn from population genetics, microbiology and ecology, are placed together, reviewed, and explained within a clear, coherent and transparent theoretical framework. Implementing the diffusion approximation we show that in all these systems (including discrete and continuous dynamics, with overlapping and non-overlapping generations) the ratio between the expected growth and its variance governs both qualitative and quantitative features of persistence and invasibility. We further clarify the relationships between bet-hedging strategies, generation time and SIS, study the dynamics of extinction when SIS fails and the explain effects of species richness and asymmetric competition on the stabilizing mechanism.

scholarly journals Low virulence evolves as a bet-hedging strategy in fluctuating environment

2015 ◽  
Author(s):  
Anne Nguyen ◽  
Etienne Rajon ◽  
David Fouchet ◽  
Dominique Pontier ◽  
Jorge Rabinovich ◽  
...  
Keyword(s):  
Adaptive Dynamics ◽  
Environmental Stochasticity ◽  
Bet Hedging ◽  
Hedging Strategy ◽  
Insect Ecology ◽  
Evolution Of Virulence ◽  
Evolutionary Epidemiology ◽  
Long Time ◽  
Environmental Variations ◽  
Risk Spreading

The effect of fluctuating environmental conditions (i.e. environmental stochasticity) on the evolution of virulence has been broadly overlooked, presumably due to a lack of connection between the fields of evolutionary epidemiology and insect ecology. Practitioners of the latter have known for a long time that stochastic environmental variations can impact the population dynamics of many insects, some of which are vectors of infectious diseases. Here we investigate whether environmental stochasticity affecting a vector's life history can have an indirect impact on the evolutionarily expected virulence of the parasite, using Chagas disease as an example. We model the evolution of virulence using the adaptive dynamics framework, showing that parasite virulence should decrease when the vector's dynamics randomly change in time. The decrease is even more pronounced when environmental variations are frequent and ample. This decrease in virulence can be viewed as a bet-hedging strategy: when a parasite is at a risk of not being transmitted (e.g. because vectors are scarce), its best option is to stay in the host longer - that is, to be less virulent. Lowering virulence is thus very similar to increasing iteroparity, a well-known risk-spreading strategy, and should be expected to evolve whenever parasite transmission varies randomly in time.

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