Broad Niche Overlap Research Articles

Niches of nine mangrove species in a Sonneratia apetala-colonized area of Dongzhai Harbor, Hainan Island, China.

The distribution of mangroves is influenced by the environment. We aimed to understand the ecological adaptability of various mangrove species within the range of the exotic species, Sonneratia apetala Buch.‐Ham., in Dongzhai Harbor, Hainan Island, China. We used three niche breadth indexes (Simpson, Levins, and Shannon–Weiner) and two niche overlap indexes (Pianka and Levins) to quantitatively determine the niche characteristics of nine mangrove species. The results showed that the order of the niche breadth values of mangrove species was as follows: Aegiceras corniculatum (Linn.) Blanco > Kandelia obovata Sheue et al. > Bruguiera gymnorrhiza (L.) Poir. > Avicennia marina (Forsk.) Vierh. Hailanci > S. apetala > S. caseolaris (L.) Engl. > Rhizophora stylosa Griff > Ceriops tagal (Perr.) C. B. Rob. > B. sexangula (Lour.) Poir. Pearson correlation analysis revealed that the niche breadth of each population was significantly correlated with the importance value of the population in the whole sample (R1 = R2 = 0.771, R3 = 0.644, p < .05). The nine mangrove species were divided into three groups by Bray–Curtis cluster analysis; the groups were similar to the distribution of mangrove species in the natural state as determined by tide level. Niche similarity analysis showed that the niche similarity of most mangroves ranged between 0.5 and 0.8 and that the species pairs A. corniculatum–B. gymnorrhiza, A. corniculatum–Avicennia marina, and K. obovata–S. caseolaris were characterized by large niche similarity ratios. Although it had a moderate niche breadth, S. apetala had a relatively broad niche overlap with mangroves in the mid‐ and low‐tide zones (S. caseolaris, A. corniculatum, K. obovata, and Avicennia marina), a moderate overlap with B. gymnorrhiza and R. stylosa, only a slight overlap with C. tagal, and no overlap with B. sexangular. There was no obvious linear relationship between niche width and niche overlap of mangroves. Due to its inefficiency in utilizing certain resources and relatively high degree of resource selection, it seems likely that S. apetala will not pose a threat to the survival of native plants, let alone completely replace native species.

New records and a revision of the actual and potential distribution of Discoglossus montalentii to facilitate future conservation assessments

Abstract The Corsican Painted Frog Discoglossus montalentii has received little research attention since its discovery, which creates uncertainty about its distribution and conservation status. We here use a combination of field surveys, ecological niche modelling (ENM) and niche overlap analyses to (i) update the D. montalentii distribution; (ii) determine its potential range, and (iii) assess if presence of Discoglossus sardus influences that of D. montalentii. Our surveys reveal presence of D. montalentii at low and mid-altitudes throughout Cap Corse and near the north-western coast, while ENMs suggest that similar climatically and topographically suitable habitats occur beyond the confirmed range in northern- and westernmost Corsica. No evidence for competitive exclusion by D. sardus was found, with both species displaying broad niche overlap at macroscale. Whether potential differences between these species do exist at microhabitat level remains worth exploring. We finally review the conservation status of D. montalentii, and assemble practical knowledge to inform future conservation assessments.

Temperature effects on the distribution of two invasive tilapia species (Tilapia zillii and Oreochromis niloticus) in the rivers of South China

Competitive interactions not only exist between invasive and native fish species but also between different invasive species, especially between those that have broad niche overlap. Nile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia zillii) are the most common invasive tilapia species in the rivers of South China. There may be specific factors that influence their competitive interactions and disturbance patterns, and temperature has been considered the most important factor. To study how temperature affects the distribution patterns and competitive interactions of these two invasive tilapia species, field surveys and laboratory experiments were conducted. Field surveys showed that latitude affected the ratio but not the biomass of all tilapia species. Nile tilapia was more abundant in the southern (warmer) sites, and Redbelly tilapia was more abundant in the northern (colder) sites. The distribution patterns of the two tilapia species were also related to latitude and minimum winter temperature. The results of the laboratory-based temperature experiments further confirmed that Redbelly tilapia can tolerate lower temperatures than Nile tilapia. However, the Nile tilapia were larger in field surveys, and laboratory experiments also showed that Nile tilapia are stronger competitors in warmer water because of their larger body size. Therefore, we suggest that the distribution patterns of these two invasive tilapia species were related to temperature conditions.

Pure polyploidy: Closing the gaps in autopolyploid research

AbstractPolyploidy (whole‐genome duplication, WGD) is an integral feature of eukaryotic evolution with two main forms typically recognized, autopolyploidy and allopolyploidy. In plants, a growing body of research contradicts historical assumptions that autopolyploidy is both infrequent and inconsequential in comparison to allopolyploidy. However, the legacy of these assumptions still persists through a lack of research on central facets of autopolyploid evolution. This review highlights recent research that has significantly increased scientific understanding of autopolyploidy. Key advances include: 1) unreduced female gametes contribute disproportionally to polyploidization through the formation of triploids, 2) niche divergence in autopolyploids can occur immediately or gradually after WGD through a diverse set of mechanisms, but broad niche overlap is also common between diploids and autopolyploids, and 3) the degree of genomic and transcriptomic changes following WGD is lower in autopolyploids than allopolyploids, but is highly variable both within and between species in both types of polyploids. We discuss the implications of these and other recent findings, present promising systems for future research, and advocate for expanded research in diverse areas of autopolyploid evolution.

Broad Niche Overlap between Invasive Nile Tilapia Oreochromis niloticus and Indigenous Congenerics in Southern Africa: Should We be Concerned?

This study developed niche models for the native ranges of Oreochromis andersonii, O. mortimeri, and O. mossambicus, and assessed how much of their range is climatically suitable for the establishment of O. niloticus, and then reviewed the conservation implications for indigenous congenerics as a result of overlap with O. niloticus based on documented congeneric interactions. The predicted potential geographical range of O. niloticus reveals a broad climatic suitability over most of southern Africa and overlaps with all the endemic congenerics. This is of major conservation concern because six of the eight river systems predicted to be suitable for O. niloticus have already been invaded and now support established populations. Oreochromis niloticus has been implicated in reducing the abundance of indigenous species through competitive exclusion and hybridisation. Despite these well-documented adverse ecological effects, O. niloticus remains one of the most widely cultured and propagated fish species in aquaculture and stock enhancements in the southern Africa sub-region. Aquaculture is perceived as a means of protein security, poverty alleviation, and economic development and, as such, any future decisions on its introduction will be based on the trade-off between socio-economic benefits and potential adverse ecological effects.

Niches of Major Associated Species in Natural Mixed Moso Bamboo Forests

Niche characteristics of nineteen main associated tree populations in moso bamboo mixed forests in Luoboyan Natural Reserve were investigated. The results show that associated populations ofSarcandra glabra,Ilex purpureaandEurya japonica, with high important values have great capacity of adapting to environment and also have broader niche breadths.Liquidamba formosanaseldom appear as associated trees and have narrow niche breadth.Castanopsis fargesii,Engelhardia fenzelii,Castanopsis kawakamii,Schima superba,Nyssa aquaticandCarpinus turczaninowiihave close niche breadth and similar distribution range within the community.Ilex purpurea-Castanopsis fargesii,Ilex purpurea-Engelhardia fenzelii,Engelhardia fenzelii-Liquidamba formosana,Castanopsis kawakamii-Dendropanax dentiger,Rhododendron pulchrum-Schima superba,Dendropanax dentiger-Castanopsis lamontiiandCastanopsis lamontii-Carpinus turczaninowiihave high niche overlaps which prove that species having similar or same circumstances demands high niche overlap indexes. Species with broader niches have more chances for niche overlap with other species.Sarcandra glabradistributes widely and has broad niche breadth but low overlap index with other species, which indicates that species with broad niche breadth is not inevitable to have broad niche overlap with other species.

Spatial and environmental effects on hydrophytic macrophyte occurrence in the Upper Rhine floodplain (Germany)

The occurrence of exclusively submerged macrophytes (hydrophytes) was analyzed on a data set of 608 mapped stream segments with a total length of 106 km from the Upper Rhine floodplain. There were three objectives. The first was to test the evidence of plot-sized bias which occurs when structural homogenous river sections are mapped. In the dataset, with a broad range of areas sampled, this bias was small but the mapping procedure nevertheless had some disadvantages for ecological interpretation of hydrophyte data. The second objective was to test for spatial autocorrelation of species composition among consecutive stream sections. Results showed that spatial autocorrelation is an intrinsic and not easily interpretable feature, which might weaken the interpretative strength of pure species–environment relationships in streams. The third objective was to analyse species–environment relationships, by redundancy analysis. The analyses gave satisfying distribution patterns of the 25 most frequent hydrophytes, using a small group of environmental parameters—current, shading, turbidity and maximum depth. They could be assigned into three groups—rheophilic, potamale and related to groundwater influence. The high amount of unexplained variability in species data is due to the large data set where the high plasticity of most hydrophytes becomes apparent and thus resulting in a broad niche overlap. The study gives a representative overview over one of the richest regions in Germany for hydrophytes.

SEEDLING SURVIVAL AND GROWTH OF THREE FOREST TREE SPECIES: THE ROLE OF SPATIAL HETEROGENEITY

Spatial heterogeneity in microenvironments may provide unique regeneration niches for trees and may promote forest diversity. We examined how heterogeneity in understory cover, mineral nutrients, and moisture and their interactions with canopy gaps contribute to the coexistence of three common, co-occuring tree species. We measured survival and height growth of 1080 seedlings of Acer rubrum (red maple), Liriodendron tulipifera (yellow poplar), and Quercus rubra (red oak) that were planted in one of five understory treatments: removal of understory vegetation, trenched, trenched plus removal of understory vegetation, fertilization, and a control. Understory treatments were replicated in 12 paired gap and canopy environments. Survivorship varied among species, with Q. rubra having the highest probability of surviving beyond the 1135-day experiment (probability = 0.64), followed by A. rubrum (probability = 0.27) and L. tulipifera (probability = 0.07). Although canopy gaps and understory treatments had large effects on survivorship, species survival rankings changed little across microenvironments; Q. rubra had the highest survival in all microenvironments. In contrast to survival, L. tulipifera had a relative growth rate for height that was three times greater than that of A. rubrum and Q. rubra in high-resource microenvironments. There was broad overlap among species in relative growth rates in the remaining seven microenvironments, with no clear top-ranked species. Differences in seedling growth and survival across these 10 microenvironments may contribute to the coexistence of two of the three species studied, L. tulipifera and Q. rubra, but not A. rubrum. Q. rubra had higher survival than A. rubrum and L. tulipifera in all microenvironments, but L. tulipifera tended to grow faster than A. rubrum and Q. rubra in high-resource microenvironments. Despite the generally poor performance of A. rubrum, it was the only surviving species in some quadrats at the end of the experiment, indicating that stochastic effects, in conjunction with broad niche overlap, may also contribute to species coexistence. The importance of stochastic effects will probably increase when differential fecundity across these three species is considered because the high fecundity of A. rubrum offsets survival and growth disadvantages of its seedlings through their greater total abundance.

Interspecific and Intraspecific Competition among Pinworms in the Hindgut of Periplaneta americana

To determine the relative importance of inter- and intraspecific factors in regulating number and fecundity of pinworms in the hindgut of Periplaneta americana, repeated samples of roaches, each consisting of an adult male, an adult female, a late instar, and an early instar, were collected from each of 2 colonies, 1 colony (mixed) infected with Thelastoma sp., Hammerschmidtiella diesingi, and Leidynema appendiculatum and the other (isolate) infected with only the last-named species. Roaches were dissected, volume of hindgut estimated, and the number of female worms of each species was recorded. Female worms were dissected and the number of uterine eggs was counted. Gut volume was a significant predictor of numbers of all species except H. diesingi, numbers of which were correlated positively with those of its 2 interspecific associates. There was little evidence of interspecific competition within the host. In the mixed colony, L. appendiculatum occurred with Thelastoma sp. less often than expected, but this was the only negative interspecific interaction observed. Fecundity was not significantly correlated with numbers of interspecifics but was strongly and negatively cor- related with numbers of intraspecifics in all species. Leidynema appendiculatum occurred at about the same intensity in isolate and mixed colonies. These results suggest that the number of each species is independently regulated. Typically this occurs through nonoverlapping niches, but all evidence points to there being broad niche overlap in the species. Unpublished findings suggest that L. appendiculatum and Thelastoma sp. limit their own numbers by intraspecific interference, a phenomenon reported in several other pinworms. Reduced fecundity is presumably a sublethal manifestation of this interference. We propose that intraspecific interference holds numbers of each species below carrying capacity and permits their coexistence despite broad niche overlap. Prevalence was below 50% in the mixed colony and was 100% in the isolate colony. This suggests that the community in the mixed colony is the result of a 2-stage process where interspecific effects play an important role in establishment of a species but where intraspecific effects dominate the in-host environment.

Niche Breadth and Overlap of Four Species of Sphagnum in Southern Ecuador

Niche breadth and overlap values ofS. magellanicum, S. recurvum, S. sancto-joseph- ense, and S. subsecundum var. rufescens from four peatlands in southern Ecuador are similar to those reported for Sphagnum-dominated peatlands in North America. The pH, conductivity, and concentrations ofFe, K, Mg, Mn, Na, and P indicate that these peatlands are similar to intermediate or transitional poor fens in the Northern Hemisphere. Niche diversification of Sphagnum in North America has been investigated by Vitt and Slack (1984). They examined microhabitat parameters of conductivity, pH, Ca, K, Mg, Na, height above the water table, and shade for 13 Sphagnum species in northern Minnesota. Calculations of niche breadth and overlap suggested independent species utiliza- tion of the gradients. In the peatlands they exam- ined, they found that niche breadths of Ca and pH become narrower from hollow to hummock, but the broadest niche breadths were for midhummock spe- cies along the height gradient. Individual species appear to interact independently to different gra- dients. This led Vitt and Slack to conclude that species of Sphagnum are largely equilibrium species as opposed to fugitive species. Slack (1982) suggests that equilibrium species have well-defined niches distinct from close competitors, whereas fugitive species are characterized by strong niche overlap with similar species. Vitt and Slack (1984) noted an exception with one species, S. russowii Warnst., which they believe to be a fugitive species since it is found in a wider range of habitats than the other species. The broad niche overlap of such species is attributed to the ruderal nature (Andrus 1986). Andrus (1986) does not quite agree with Slack's (1982) interpretation that Sphagnum species are best classed as equilibrium species. He feels that this is probably more appropriate for species in well-de- veloped and slowly evolving peatlands. The distri- bution of Sphagnum in peatlands is envisioned by Slack (1982) as a function of colonizing ability and competitive interactions since the last disturbance event, with the establishment of Sphagnum as a short phase compared to growth of the Sphagnum in an established peatland, which is viewed as a relatively long-lived habitat. However, Andrus notes that periodic drought and fire are common phe- nomena in northern peatlands. Such disturbances create short-lived habitats that are often character- istic of fugitive species.

Interference competition as a mechanism of coexistence between two sympatric species of the grass shrimp Palaemonetes (Decapoda: Palaemonidae)

Various theories have been developed to explain the puzzling coexistence of species which have broad niche overlap in critical resource utilization. The coexistence of two sympatric species of grass shrimp, Palaemonetes pugio Holthuis and P. vulgaris (Say), whose niches overlap with respect to space, food, and time, was examined in an experimental field and laboratory study. A seasonal fluctuation between sympatric and contiguous allopatric distribution of the two species of grass shrimp on natural shell, mud, and eelgrass substrata suggests that competition may be an important factor determining distribution of Palaemonetes. Field and laboratory experiments confirm that P. vulgaris can competitively displace P. pugio from the preferred shell substratum by interference competition but the tendency of grass shrimp to separate spatially in winter by bottomdepths (as in field enclosure cages) could have allowed both species to coexist on shell. Spatial separation by bottom-depth was not so evident in spring, since P. vulgaris apparently displaced P. pugio from shell to mud substratum. Occupancy of shell substratum is shown to be adaptive in that shell provides greater protection from predators than does mud. It is suggested that the spatial partitioning resulting from this interference competition promotes coexistence by reducing agonism while permitting efficient utilization of other common resources.

An Analysis of the Feeding Ecology of the Salamanders (Amphibia, Urodela) of the Hubbard Brook Experimental Forest, New Hampshire

The gut contents of 486 salamanders representing all five species (Plethodon cinereus, Desmognathus fuscus, Eurycea bislineata, Gyrinophilus porphyriticus, and Notophthalmus viridescens) occurring in the northern hardwoods forest of central New Hampshire were analyzed. These data show that there is broad niche overlap in the feeding ecology of the five species but spatial (habitat) separation, and gradients in size of adult salamanders effectively reduce competition for food resources. The food habits of all five species in the forest are described in detail. Generally, all five species are euryphagic predators and feed on any food they can capture in the proper size category.