NULL MODELS OF EXOTIC INVASION AND SCALE-DEPENDENT PATTERNS OF NATIVE AND EXOTIC SPECIES RICHNESS

Ecology ◽  
2004 ◽  
Vol 85 (12) ◽  
pp. 3215-3222 ◽  
Author(s):  
Jason D. Fridley ◽  
Rebecca L. Brown ◽  
John F. Bruno
Keyword(s):  
Species Richness ◽  
Exotic Species ◽  
Null Models ◽  
Exotic Invasion

scholarly journals Worldwide patterns in species richness of falconiformes: analytical null models, geometric constraints, and the mid-domain effect

2004 ◽  
Vol 64 (2) ◽  
pp. 209-308
Author(s):  
T. F. L.V. B. Rangel ◽  
J. A. F. Diniz-filho
Keyword(s):  
Species Richness ◽  
Primary Productivity ◽  
Net Primary Productivity ◽  
Empirical Support ◽  
Null Models ◽  
Geometric Constraints ◽  
Global Level ◽  
Spatial Gradients ◽  
Available Energy ◽  
Surrogate Variable

Recently, the hypothesis that the geographic distribution of species could be influenced by the shape of the domain edges, the so-called Mid-Domain Effect (MDE), has been included as one of the five credible hypotheses for explaining spatial gradients in species richness, despite all the unsuccessful current attempts to prove empirically the validity of MDE. We used data on spatial worldwide distributions of Falconiformes to evaluate the validity of MDE assumptions, incorporated into two different sorts of null models at a global level and separately across five domains/landmasses. Species richness values predicted by the null models of the MDE and those values predicted by Net Primary Productivity, a surrogate variable expressing the effect of available energy, were compared in order to evaluate which hypothesis better predicts the observed values. Our tests showed that MDE continues to lack empirical support, regardless of its current acceptability, and so, does not deserve to be classified as one possible explanation of species richness gradients.

Exotic plant invasion and understorey species richness: a comparison of two types of eucalypt woodland in agricultural Western Australia

1998 ◽  
Vol 4 (1) ◽  
pp. 21 ◽  
Author(s):  
Max Abensperg-Traun ◽  
Lyn Atkins ◽  
Richard Hobbs ◽  
Dion Steven
Keyword(s):  
Species Richness ◽  
Exotic Species ◽  
Plant Species ◽  
Plant Invasion ◽  
Native Plants ◽  
Exotic Plants ◽  
Exotic Plant ◽  
Native Plant ◽  
Road Verge ◽  
Exotic Plant Invasion

Exotic plants are a major threat to native plant diversity in Australia yet a generic model of the invasion of Australian ecosystems by exotic species is lacking because invasion levels differ with vegetation/soil type and environmental conditions. This study compared relative differences in exotic species invasion (percent cover, spp. richness) and the species richness of herbaceous native plants in two structurally very similar vegetation types, Gimlet Eucalyptus salubris and Wandoo E. capillosa woodlands in the Western Australian wheatbelt. For each woodland type, plant variables were measured for relatively undisturbed woodlands, woodlands with >30 years of livestock grazing history, and woodlands in road-verges. Grazed and road-verge Gimlet and Wandoo woodlands had significantly higher cover of exotic species, and lower species richness of native plants, compared with undisturbed Gimlet and Wandoo. Exotic plant invasion was significantly greater in Gimlet woodlands for both grazed (mean 78% cover) and road-verge sites (mean 42% cover) than in comparable sites in Wandoo woodlands (grazed sites 25% cover, road-verge sites 19% cover). There was no significant difference in the species richness of exotic plants between Wandoo and Gimlet sites for any of the three situations. Mean site richness of native plants was not significantly different between undisturbed Wandoo and undisturbed Gimlet woodlands. Undisturbed woodlands were significantly richer in plant species than grazed and road-verge woodlands for both woodland types. Grazed and road-verge Wandoo sites were significantly richer in plant species than communities in grazed and road-verge Gimlet. The percent cover of exotics was negatively correlated with total (native) plant species richness for both woodland types (Wandoo r = ?0.70, Gimlet r = ?0.87). Of the total native species recorded in undisturbed Gimlet, 83% and 61% were not recorded in grazed and road-verge Gimlet, respectively. This compared with 40% and 33% for grazed and road-verge Wandoo, respectively. Grazed Wandoo and grazed Gimlet sites had significantly fewer native plant species than did road-verge Wandoo and road-verge Gimlet sites. Ecosystem implications of differential invasions by exotic species, and the effects of grazing (disturbance) and other factors influencing susceptibility to exotic plant invasion (landscape, competition and allelopathy) on native species decline are discussed. Exclusion of livestock and adequate methods of control and prevention of further invasions by exotic plants are essential requirements for the conservation of these woodland systems.

Null models and spatial patterns of species richness in South American birds of prey

2002 ◽  
Vol 5 (1) ◽  
pp. 47-55 ◽  
Author(s):  
Jose Alexandre Felizola Diniz-Filho ◽  
Carlos Eduardo Ramos de Sant'Ana ◽  
Marcia Christianne de Souza ◽  
Thiago F. L. V. B. Rangel
Keyword(s):  
Species Richness ◽  
Spatial Patterns ◽  
Null Models ◽  
Birds Of Prey ◽  
South American

Vegetation change in an urban grassy woodland 1974 - 2000

2004 ◽  
Vol 52 (5) ◽  
pp. 597 ◽  
Author(s):  
J. B. Kirkpatrick
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Exotic Species ◽  
Native Species ◽  
Vegetation Change ◽  
Structural Changes ◽  
Linear Models ◽  
Tree Cover ◽  
Native Plant ◽  
Native Species Richness

Few temporal studies document vegetation change in Australian temperate grassy woodlands. Floristic and structural data were collected from 68 randomly located sites in the Queens Domain, an urban grassy woodland remnant, in 1974, 1984, 1994 and 2000 and a search made for rare species. Species of conservation significance were concentrated at highly disturbed sites, whereas vegetation types of conservation significance decreased in area as a result of increases in the numbers of Allocasuarina verticillata, which caused a change in many unmown areas from Eucalyptus viminalis grassy woodland to E. viminalis–A. verticillata woodland/forest or A. verticillata open/closed forest. Structural changes were associated with changes in species composition and an increase in native-species richness. Increases in tree cover occurred where fires were most frequent, possibly as a result of the lack of mammalian herbivores. The frequencies of herbs and annual grasses were strongly affected by precipitation in the month of sampling. Half of the species that showed a consistent rise or fall through time were woody plants, approximately twice the number expected. In the dataset as a whole, species-richness variables were largely explained by varying combinations of variables related to moisture availability, altitude and the incidence of mowing. The strongest influences on species composition were the same, although slope and time since the last fire also contributed to multiple regression and generalised linear models. Compositional stability was positively related to native-species richness, whereas high levels of exotic-species richness occurred at both low and high levels of native-species richness. The maintenance of native-plant biodiversity on the Domain requires such counterintuitive measures as the maintenance of exotic trees and the control of native trees, demonstrating the contingencies of conservation management in fragmented vegetation that consists of a mixture of native and exotic species.

Germination response to heat and smoke of 22 Poaceae species from grassy woodlands

2005 ◽  
Vol 53 (5) ◽  
pp. 445 ◽  
Author(s):  
S. Clarke ◽  
K. French
Keyword(s):  
Heat Treatment ◽  
Species Richness ◽  
Exotic Species ◽  
Fire Regime ◽  
Fire Regimes ◽  
Grass Species ◽  
Percentage Germination ◽  
Germination Response ◽  
Eastern Australia ◽  
Smoke Water

Grasses form an important component of grassy woodlands, although their response to fire has been understudied. In this study, fire germination responses of 22 Poaceae species from an endangered grassy-woodland community in eastern Australia were investigated. Seeds of 20 native and two exotic species were subjected to heat (no heat, 40, 80 and 120°C) and smoke treatment (10% dilution smoke water) and the percentage germination was compared. Germination response of species showed no consistent pattern to phylogeny and was highly variable. Germination in six species was unaffected by the application of heat or smoke. In five species, heat, irrespective of smoke application, influenced germination. Smoke, irrespective of heat treatment, influenced six species. For a further six species, the effect of smoke varied with temperature. These results suggest that fire regimes will influence the recruitment of grass species differentially and maintaining regional species richness is likely to require the maintenance of a heterogeneous fire regime across the landscape.

scholarly journals Species richness, phylogenetic diversity and phylogenetic structure patterns of exotic and native plants along an elevational gradient in the Himalaya

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Kumar Manish
Keyword(s):  
Species Richness ◽  
Exotic Species ◽  
Native Species ◽  
Phylogenetic Diversity ◽  
Elevational Gradient ◽  
Species Assemblages ◽  
Native Plant ◽  
Phylogenetic Structure ◽  
Phylogenetic Overdispersion ◽  
The Himalaya

Abstract Background So far, macroecological studies in the Himalaya have mostly concentrated on spatial variation of overall species richness along the elevational gradient. Very few studies have attempted to document the difference in elevational richness patterns of native and exotic species. In this study, this knowledge gap is addressed by integrating data on phylogeny and elevational distribution of species to identify the variation in species richness, phylogenetic diversity and phylogenetic structure of exotic and native plant species along an elevational gradient in the Himalaya. Results Species distribution patterns for exotic and native species differed; exotics tended to show maximum species richness at low elevations while natives tended to predominate at mid-elevations. Native species assemblages showed higher phylogenetic diversity than the exotic species assemblages over the entire elevational gradient in the Himalaya. In terms of phylogenetic structure, exotic species assemblages showed majorly phylogenetic clustering while native species assemblages were characterized by phylogenetic overdispersion over the entire gradient. Conclusions The findings of this study indicate that areas with high native species richness and phylogenetic diversity are less receptive to exotic species and vice versa in the Himalaya. Species assemblages with high native phylogenetic overdispersion are less receptive to exotic species than the phylogenetically clustered assemblages. Different ecological processes (ecological filtering in case of exotics and resource and niche competition in case of natives) may govern the distribution of exotic and native species along the elevational gradient in the Himalaya.

scholarly journals A century of ecosystem change: human and seabird impacts on plant species extirpation and invasion on islands

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2208 ◽  
Author(s):  
Thomas K. Lameris ◽  
Joseph R. Bennett ◽  
Louise K. Blight ◽  
Marissa Giesen ◽  
Michael H. Janssen ◽  
...  
Keyword(s):  
Species Richness ◽  
Exotic Species ◽  
Plant Species ◽  
Plant Communities ◽  
Soil Depth ◽  
Rapid Change ◽  
Ecosystem Change ◽  
Native Plant ◽  
Native Plant Species ◽  
Species Cover

We used 116 years of floral and faunal records from Mandarte Island, British Columbia, Canada, to estimate the indirect effects of humans on plant communities via their effects on the population size of a surface-nesting, colonial seabird, the Glaucous-winged gull (Larus glaucescens). Comparing current to historical records revealed 18 extirpations of native plant species (32% of species historically present), 31 exotic species introductions, and one case of exotic introduction followed by extirpation. Contemporary surveys indicated that native species cover declined dramatically from 1986 to 2006, coincident with the extirpation of ‘old-growth’ conifers. Because vegetation change co-occurred with an increasing gull population locally and regionally, we tested several predictions from the hypothesis that the presence and activities of seabirds help to explain those changes. Specifically, we predicted that on Mandarte and nearby islands with gull colonies, we should observe higher nutrient loading and exotic plant species richness and cover than on nearby islands without gull colonies, as a consequence of competitive dominance in species adapted to high soil nitrogen and trampling. As predicted, we found that native plant species cover and richness were lower, and exotic species cover and richness higher, on islands with versus without gull colonies. In addition, we found that soil carbon and nitrogen on islands with nesting gulls were positively related to soil depth and exotic species richness and cover across plots and islands. Our results support earlier suggestions that nesting seabirds can drive rapid change in insular plant communities by increasing nutrients and disturbing vegetation, and that human activities that affect seabird abundance may therefore indirectly affect plant community composition on islands with seabird colonies.

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