Niche Modification Research Articles

Effect of habitat degradation on competition, carrying capacity, and species assemblage stability.

Changes in species’ trophic niches due to habitat degradation can affect intra‐ and interspecific competition, with implications for biodiversity persistence. Difficulties of measuring species’ interactions in the field limit our comprehension of competition outcomes along disturbance gradients. Thus, information on how habitat degradation can destabilize food webs is scarce, hindering predictions regarding responses of multispecies systems to environmental changes. Seagrass ecosystems are undergoing degradation. We address effects of Posidonia oceanica coverage reduction on the trophic organization of a macroinvertebrate community in the Tyrrhenian Sea (Italy), hypothesizing increased trophic generalism, niche overlap among species and thus competition and decreased community stability due to degraded conditions. Census data, isotopic analysis, and Bayesian mixing models were used to quantify the trophic niches of three abundant invertebrate species, and intra‐ and interspecific isotopic and resource‐use similarity across locations differing in seagrass coverage. This allowed the computation of (1) competition strength, with respect to each other and remaining less abundant species and (2) habitat carrying capacity. To explore effects of the spatial scale on the interactions, we considered both individual locations and the entire study area (“‘meadow scale”). We observed that community stability and habitat carrying capacity decreased as P. oceanica coverage declined, whereas niche width, similarity of resource use and interspecific competition strength between species increased. Competition was stronger, and stability lower, at the meadow scale than at the location scale. Indirect effects of competition and the spatial compartmentalization of species interactions increased stability. Results emphasized the importance of trophic niche modifications for understanding effects of habitat loss on biodiversity persistence. Calculation of competition coefficients based on isotopic distances is a promising tool for describing competitive interactions in real communities, potentially extendible to any subset of ecological niche axes for which specimens’ positions and pairwise distances can be obtained.

Differential effects of dominant and subordinate plant species on the establishment success of target species in a grassland restoration experiment

AbstractQuestionsWe investigated how the establishment of sown target species for ecological restoration is affected by the early introduction of either dominant or subordinate species during the assembly of a restored topsoil‐stripped, nutrient‐poor grassland. Do dominant or subordinate species exert different priority effects on either wanted target species or unwanted pioneer species? If priority effects are detected, are these exerted via niche preemption or niche modification mechanisms? Are the resulting patterns of species establishment related to differences in functional trait composition?LocationMeerdaal forest, Oud‐Heverlee, Belgium.MethodsA 2‐yr field experiment on a topsoil‐stripped site of 8.5 ha was carried out. We manipulated the early arrival of dominant and subordinate species. The ‘dominant species’ set consisted of three generalist grass species, and the ‘subordinate species’ set consisted of nine species of forbs and graminoids that often occur in nutrient‐poor grasslands. After 4 wk, we sowed nine target species for ecological restoration. We recorded plant species cover during 2 yr. We used repeated measures ANOVA to test for effects of time (2013, 2014) and treatment (dominant, subordinate and control) on plant species richness, evenness, cover, functional diversity and species and trait composition dissimilarity.ResultsBoth dominant and subordinate species successfully suppressed undesirable early colonizing species. Dominants did not exert priority effects on target species. However, subordinate species exerted strong priority effects via niche preemption, and suppressed their establishment of target species.ConclusionsManipulating the arrival order of dominant species has potential as a restoration tool that can allow restoration practitioners to enhance the establishment success of target species for restoration. We suggest that seed mixtures for restoration should contain dominant species, because they will not affect the establishment of subordinate (target) species, but will impede the establishment of unwanted pioneer and ruderal species. We also demonstrate that implementing trait‐based measures in restoration projects can help to adequately predict assembly processes.

A test of priority effect persistence in semi-natural grasslands through the removal of plant functional groups during community assembly.

BackgroundIt is known that during plant community assembly, the early colonizing species can affect the establishment, growth or reproductive success of later arriving species, often resulting in unpredictable assembly outcomes. These so called ‘priority effects’ have recently been hypothesized to work through niche-based processes, with early colonizing species either inhibiting the colonization of other species of the same niche through niche preemption, or affecting the colonization success of species of different niches through niche modification. With most work on priority effects performed in controlled, short-term mesocosm experiments, we have little insight in how niche preemption and niche modification processes interact to shape the community composition of natural vegetations. In this study, we used a functional trait approach to identify potential niche-based priority effects in restored semi-natural grasslands. More specifically, we imposed two treatments that strongly altered the community’s functional trait composition; removal of all graminoid species and removal of all legume species, and we compared progressing assembly with unaltered control plots.ResultsOur results showed that niche preemption effects can be, to a limited extent, relieved by species removal. This relief was observed for competitive grasses and herbs, but not for smaller grassland species. Although competition effects acting within functional groups (niche preemption) occurred for graminoids, there were no such effects for legumes. The removal of legumes mainly affected functionally unrelated competitive species, likely through niche modification effects of nitrogen fixation. On the other hand, and contrary to our expectations, species removal was after 4 years almost completely compensated by recolonization of the same species set, suggesting that priority effects persist after species removal, possibly through soil legacy effects.ConclusionsOur results show that both niche modification and niche preemption priority effects can act together in shaping community composition in a natural grassland system. Although small changes in species composition occurred, the removal of specific functional groups was almost completely compensated by recolonization of the same species. This suggests that once certain species get established, it might prove difficult to neutralize their effect on assembly outcome, since their imposed priority effects might act long after their removal.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0077-9) contains supplementary material, which is available to authorized users.

Historical Contingency in Community Assembly: Integrating Niches, Species Pools, and Priority Effects

The order and timing of species immigration during community assembly can affect species abundances at multiple spatial scales. Known as priority effects, these effects cause historical contingency in the structure and function of communities, resulting in alternative stable states, alternative transient states, or compositional cycles. The mechanisms of priority effects fall into two categories, niche preemption and niche modification, and the conditions for historical contingency by priority effects can be organized into two groups, those regarding regional species pool properties and those regarding local population dynamics. Specifically, two requirements must be satisfied for historical contingency to occur: The regional pool contains species that can together cause priority effects, and local dynamics are rapid enough for early-arriving species to preempt or modify niches before other species arrive. Organizing current knowledge this way reveals an outstanding key question: How are regional species pools that yield priority effects generated and maintained?

Cancer Ecology: Niche Construction, Keystone Species, Ecological Succession, and Ergodic Theory

Parallels between cancer and ecological systems have been increasingly recognized and extensively reviewed. However, a more unified framework of understanding cancer as an evolving dynamical system that undergoes a sequence of interconnected changes over time, from a dormant microtumor to disseminated metastatic disease, still needs to be developed. Here, we focus on several examples of such mechanisms, namely, how in cancer niche construction a metabolic adaptation and consequent change to the tumor microenvironment (niche modification) becomes an important factor in evasion of the predator (immune system), facilitating disease progression; how tumor establishment and propagation is driven by the tumor’s own keystone species, the cancer stem cells; and how the succession of stages of metastatic dissemination can be informed by ergodic theory and forest ecology.

Effects of organic pollution on biological communities of marine biofilm on hard substrata

We examined the effect of organic enrichment on diatom and bacterial assemblages of marine epilithic biofilms on two locations in the Mediterranean, one situated in Spain and the other in Greece. Total organic carbon, total organic nitrogen, stable isotopes (δ13C and δ15N) and chlorophyll a indicated significant incorporation of organic wastes, increased primary production and trophic niche modifications on the biofilms close to the organic enrichment source. In Spain, where the organic load was higher than in Greece, diatom and, to some extent, bacterial assemblages varied following the organic enrichment gradient. The taxonomic richness of diatom and bacterial communities was not influenced by organic enrichment. Classical community parameters showed consistent patterns to organic pollution in both locations, whereas community assemblages were only influenced when organic pollution was greatest. The successional patterns of these communities were similar to other epilithic communities. The modification of community assemblages induced by organic pollution may affect ecological functions.

Niche construction initiates the evolution of mutualistic interactions.

Niche construction theory explains how organisms' niche modifications may feed back to affect their evolutionary trajectories. In theory, the evolution of other species accessing the same modified niche may also be affected. We propose that this niche construction may be a general mechanism driving the evolution of mutualisms. Drosophilid flies benefit from accessing yeast-infested fruits, but the consequences of this interaction for yeasts are unknown. We reveal high levels of variation among strains of Saccharomyces cerevisiae in their ability to modify fruits and attract Drosophila simulans. More attractive yeasts are dispersed more frequently, both in the lab and in the field, and flies associated with more attractive yeasts have higher fecundity. Although there may be multiple natural yeast and fly species interactions, our controlled assays in the lab and field provide evidence of a mutualistic interaction, facilitated by the yeast's niche modification.

Mobilization of hematopoietic stem/progenitor cells: general principles and molecular mechanisms.

Hematopoietic stem/progenitor cell mobilization can be achieved by a variety of bone marrow niche modifications, although efficient mobilization requires simultaneous expansion of the stem/progenitor cell pool and niche modification. Many of the mechanisms involved in G-CSF-induced mobilization have been described. With regard to mobilization of hematopoietic stem/progenitor cells, challenges for the future include the analysis of genetic factors responsible for the great variability in mobilization responses, and the identification of predictors of mobilization efficiency, as well as the development of mobilizing schemes for poor mobilizers. Moreover, improved regimens for enhanced or even preferential mobilization of nonhematopoietic stem/progenitor cell types, and their therapeutic potential for endogenous tissue repair will be questions to be vigorously pursued in the near future.

Dietary niche partitioning in a piscivorous fish guild in response to stocking of an additional competitor – The role of diet specialisation

Species belonging to the same ecological guild can coexist only if there are differences in their responses to limiting resources. Thus, competitor introductions may modify the niches of the resident competitors, but empirical studies are rare. The extent of niche modification might further depend on the species’ trophic specialisation along the specialists-to-generalists axis. In this study, we performed a semi-natural experiment by introducing a trophically specialised piscivorous fish (pikeperch) to the resident predator guild of a trophic generalist (perch) and a trophic specialist (pike) in a temperate freshwater lake. Individual diet data were used to calculate total niche hypervolume and inter- and intraspecific dietary niche overlap to evaluate strength of competitive interactions before and after pikeperch introduction. In both pike and perch, there was a moderate niche compression in response to pikeperch stocking. Furthermore, whereas perch diet hypervolume did not overlap at all with that of pikeperch, the intersection of niche space between the two trophic specialists was highly asymmetrical in favour of pike due to its less specialised diet composition in comparison with pikeperch. The intraspecific dietary niche overlap between perch size classes reflected an enhanced partitioning, whereas that of pike size classes was found almost unchanged in response to pikeperch stocking. These empirical results corroborate that competitive interactions and the degree of specialisation may strongly shape the success of introductions of top-predators in freshwater ecosystems. The most specialised species may persist only if the competitors belong rather to the generalists along the specialisation continuum.

Migration of Cells From the Yolk Sac to Hematopoietic Tissues After Transplantation of Early and Mid Gestation Canine Fetuses

Migration of Cells From the Yolk Sac to Hematopoietic Tissues After Transplantation of Early and Mid Gestation Canine Fetuses

Differential niche modification by males and females of a dioecious herb: extending the Jack Sprat effect

Males and females of dioecious plants often differ in morphological, physiological and life-history traits, probably as a result of their different requirements for reproduction. We found that the growth and reproductive effort of individuals of the dioecious herb Mercurialis annua depended on whether males or females had been growing in the soil previously. This suggests that males and females of M. annua differentially modify the soil in which they are growing. Our study indicates that sexual dimorphism in dioecious plants can give rise to increased environmental heterogeneity as a consequence of sex-specific niche modification.

Chondroitin Sulfate, a Major Niche Substance of Neural Stem Cells, and Cell Transplantation Therapy of Neurodegeneration Combined with Niche Modification

Chondroitin sulfate (CS), a polysaccharide moiety of proteoglycans, is one of the major components of the extracellular matrix in the central nervous system and is involved in various cellular events in the formation and maintenance of the neural network. In the developing brain, CS in the milieu of neural stem/progenitor cells (NSPCs) is believed to participate in the regulation of their functions such as proliferation and differentiation. NSPCs are expected to act as a potent cell type in cell replacement therapy for neurodegeneration in various neurological diseases. Recently, it has been shown that transplantation of NSPCs combined with removal of extracellular CS from the host nervous tissues gives a satisfactory outcome in some animal models of nervous tissue injuries including neonatal hypoxic-ischemic injury and adult spinal cord injury. The combination of cell transplantation with modification of the extracellular matrix of the host tissue could be a novel strategy for the treatment of incurable neurodegenerative diseases.

Not armour, but biomechanics, ecological opportunity and increased fecundity as keys to the origin and expansion of the mineralized benthic metazoan fauna

This paper offers a new biotic interaction hypothesis for the Cambrian ‘explosion’ of mineralized, benthic, metazoan diversity. It proposes that organic-mineral composite structures (e.g. shells and muscle lever-arms) originated in Proterozoic lineages of primary larva-like, but reproductively competent, pelagic bilaterians because mineralization was both mechanically and energetically favourable, not because it provided armour against predation. Increased strength and rigidity of composite structures permitted growth to sizes incompatible with a continued pelagic existence, while the increased density resulting from massive mineralization facilitated settlement into, and stability in, a nutrient-rich, Proterozoic benthic zone that offered new ecological opportunities. Because evolutionary success is recognized by the formation of recoverable fossils, which requires large, enduring populations, successful lineages are those that responded to the new opportunities by achieving broad niche occupancy through the evolution of metamorphosis to larger, mineralized ‘adult’ body forms with more efficient food-collecting apparatus and higher fecundity. Niche modification (e.g. reef and shell-bed formation) by early mineralized benthic settlers may have increased the likelihood of further successful settlement, leading to the appearance of a period of ‘explosive’ increase in benthic, mineralized, metazoan diversity. Predator-prey arms races may then have followed, causing early faunal turnover and possible selection for improved armour. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 483‐490. ADDITIONAL KEYWORDS: benthic settlement - Cambrian explosion ‐ metamorphosis - organic-mineral composite.

Relating Species Diversity to Ecosystem Functioning: Mechanistic Backgrounds and Experimental Approach with a Decomposer Food Web

Hypotheses have recently been formulated to elucidate the relationship between species diversity and ecosystem functioning. Using previously published mechanisms as a starting point we suggest that common mechanisms can be provided for this relationship by using the concepts of niche and trophic-level dynamics. The reasoning is the following: if remaining species within a trophic level can modify their niches as other species disappear, production within the level remains unchanged, whereas in the absence of niche modification production decreases. Decreased production within a trophic level affects biomass and production at other levels as predicted by trophic-dynamic models. Changes in biomass and production finally bring about changes in ecosystem functioning. In the redundant species hypothesis remaining species can modify their niches, and so functioning remains unchanged. In the predictable change hypothesis (our counterpart for the rivet hypothesis), and in the idiosyncratic response hypothesis, remaining species cannot modify their niches, leading to predictable and unpredictable changes in functioning, respectively. Unpredictable changes are due to differences in the characteristics of species and indirect interactions between populations. We tested the hypotheses and the suggested mechanisms using a soil food web with three trophic levels: microbes, microbivorous nematodes and a predatory nematode. We established one diverse (3 bacterivores and 3 fungivores) and three simple (1 bacterivore and 1 fungivore) food webs and found that differences in trophic-level biomasses between the diverse and simple food webs were idiosyncratic. Unpredictability resulted from differences in microbivore characteristics - their efficiency in resource utilisation and vulnerability to predation and competition. Changes in microbial respiration and total mineralisation of C and N, i.e., system functioning, were also idiosyncratic rather than redundant or predictable when diversity was reduced, although idiosyncracy was not as clear as in the case of trophic-level biomasses. We conclude that predicting the influence of declining species diversity on trophic-level dynamics and ecosystem processes is difficult, at least in food webs with a small initial number of species, unless the characteristics of species and the nature of their interactions are known.

Competitive Trophic Niche Modifications in Three Populations of Detritivores

Competitive Trophic Niche Modifications in Three Populations of Detritivores

Niche modification and stability of competitive systems. III. Simulation model analysis

SummarySimulation model for niche shift in ecological time scale was constructed on the basis of the optimal foraging theory. In accordance with the previous experimental study (Shimada andFujii, 1985), the model competitive system consisted of 2 parasitoid wasp species utilizing 4 host stages. Wasps were assumed to choose host stages in the manner that they realized the maximal gain/cost values, where gain was represented by body weight of a wasp progeny emerging from each host stage and cost was expressed by time required to search for and detect an unparasitized host. The number of parasitized hosts in each host stage was calculated numerically by usingArditt's (1983) model for avoidance of superparasitism.The model simulated well the experimental results ofShimada andFujii (1985) andShimada (1985). Sensitivity analysis of the model showed that the experimentally derived criterion for competitive coexistence (different second‐best host stages between competing species even with the common best) was not necessarily the indispensable condition for niche shift and separation, but that if the criterion was not satisfied, stable competitive coexistence occurred only in the narrow range of the parametric values. Further, niche shift in ecological time scale made the competitive coexistence more stable than fixed niche on which the current niche theory stands.

Niche modification and stability of competitive systems. II. Persistence of interspecific competitive systems with parasitoid wasps

SummaryEffects of niche shift in ecological time scale on the population dynamics of competing species were studied in the experimental populations of two parasitoid wasp species, Anisopteromalus calandrae and Heterospilus prosopidis (both are solitary parasites), on a host, the azuki bean weevil, Callosobruchus chinensis. Four resource conditions were set up with combination of kind of bean (azuki or black eye), and host distribution (uniform or clumped). In each resource condition, four developmental stages of hosts were provided as a resource spectrum for parasitoid wasps.Population dynamics of the two wasp populations were investigated in each resource condition in Multi‐Generation Competitive Systems (MGCS), in which fresh hosts of four developmental stages were periodically introduced and were parasitized competitively by the two wasp species. Competitive coexistence of both wasps occurred in the azuki‐clumped condition, where the peaks of the resource utilization curves separated in the two species; pupae in A. calandrae and the early or late fourth instar in H. prosopidis, A. calandrae was eliminated in the azuki‐uniform condition and H. prosopidis went extinct in two black eye conditions irrespective of host distributions. The degrees of overlap of the resource utilization patterns of the two wasp species during population dynamics were not significantly different among resource conditions irrespective of the results of coexistence or extinction. Even in the azuki‐clumped condition, however, extinction of A. calandrae was observed when resource partitioning could not be realized with only the late fourth instar larvae available to wasps. Further analytical experiments showed that parasitizing ability of A. calandrae increased with host density per bean with azuki beans, but A. calandrae could express higher parasitizing ability with black eye beans than H. prosopidis irrespective of host density per bean.The flexibility in parasitizing ability by A. calandrae for various host stages under different resource conditions was thought to be the major factor in determining the competitive coexistence or the extinction of either species under different resource conditions. The present experiments also suggested that different second‐best host stages between competitors could be a major contributing factor to competitive coexistence.

Niche modification and stability of competitive systems. I. Niche modification process

On mesure trois types d'utilisation des ressources chez Anisopteromalus calandrae et heterospilus prosopidis (niche preferentielle sans competition, niche avec competition intra- ou interspecifique). But des recherches: proposer une explication generale des processus de modification de la niche ecologique sous la pression de la competition a l'echelle chronologique ecologique

Niche Modification in Chaetognatha Infected with Larval Trematodes (Digenea)

AbstractInfection by larval trematode parasites caused sympatric chaetognath species to live nearer the surface than normal, hence to select more upper water prey than did non‐parasitized chaetognaths of the same species. This was associated with contagious distribution of parasites within the population.Trematode larvae appear as opaque objects in their almost transparent chaetognath hosts. Since they also induced their hosts to be larger and to live in better‐lit habitat than non‐parasitized ones, the parasites render their hosts more conspicuous and thus probably more susceptible to sight hunting fish predators. Available data from seasonal cycles of parasitism in chaetognaths confirms that trematode‐parasitized chaetognaths suffer higher mortality than normal, probably ascribable to predation. However, the size increase also may discourage predation by smaller, incorrect final host species.Localization of parasitism (which lowers individual reproductive potential). and predation in the same segment of the population should minimize loss of reproductive potential for the chaetognath population as a whole. This conservation of host resources can be considered primarily of benefit to the trematodes.Knowledge of parasite‐induced host modification should enable prediction of mode of parasite transmission, and vice‐versa. Contagious distribution of parasites in their host populations can help damp population cycling.