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1.
《Acta Oecologica》1999,20(5):499-508
Post-fire regeneration patterns (plant cover and richness) in the Valencia region (eastern Iberian Peninsula) are studied by analysing data from two different samplings after two periods of large fires (1991 and 1994). Emphasis is given to comparing different environmental conditions (thermo-Mediterranean vs. meso-Mediterranean; south facing vs. north facing slopes) and different bedrock types (limestone vs. marls). Results suggest that the highest post-fire cover and species richness is reached in thermo-Mediterranean conditions on limestone, and the main species are the resprouters Quercus coccifera and Brachypodium retusum. North-facing sites have higher plant cover than south-facing ones, and most life forms (trees, shrubs, grasses) have higher cover in these sites. Species richness is higher on north-facing sites than on the south-facing ones at the small scale (1 to 200 m2), but differences were not significant at the highest scale studied (1 000 m2). Plant species richness with increasing sampling area follows the classical log-log relationship; however, when species are segregated by life forms (woody species and herbs), different species-area relationships were found. 相似文献
2.
Lorenzo Marini Andrea Battisti Enzo Bona Germano Federici Fabrizio Martini Marco Pautasso Philip E. Hulme 《Global Ecology and Biogeography》2012,21(5):534-544
Aim To investigate whether differences in the elevational trend in native and alien species richness were dependent on climate or human pressures. Specifically we tested whether life‐form and/or alien/native status modifies the response of plant species richness to human population and temperature along: (1) a complete elevational gradient, and (2) within separate elevational bands that, by keeping temperature within a narrow range, elucidate the effects of human pressures more clearly. Location Two provinces (c. 7507 km2) on the southern border of the European Alps (Italy), subdivided into 240 contiguous sampling cells (c. 35.7 km2). Methods We used an extensive dataset on alien and native species richness across an elevation gradient (20–2900 m a.s.l.). Richness of natives and naturalized aliens were separately related to temperature, human population and Raunkiaer life‐form using general linear mixed models. Life‐form describes different plant strategies for survival during seasons with adverse cold/arid conditions. Results The relationship between species richness and temperature for natives was strongly dependent on life‐form, while aliens showed a consistent positive trend. Similar trends across alien and native life‐forms were found for the relationship between species richness and human population along the whole gradient and within separate elevational bands. Main conclusions The absence of life‐form‐dependent responses amongst aliens supports the hypothesis that the distribution of alien plant species richness was more related to propagule pressure and availability of novel niches created by human activities than to climatic filtering. While climate change will potentially contribute to relaxing species thermal constraints, the response of alien species to future warming will also be contingent on changes in anthropogenic pressures. 相似文献
3.
Laura Meneses Calvillo Virginia Meléndez Ramírez Víctor Parra-Tabla Jorge Navarro 《Journal of Insect Conservation》2010,14(4):323-334
The effects of fragmentation on tropical bee communities are not well understood. The present study investigated these effects
on wild bee species richness and diversity in fragments of tropical forest in the Yucatan Estate (Mexico). We present an analysis
of bee community structure based on fragment size, connectivity, and bee life form, and include an analysis of m-dominance to evaluate if large fragments sustain greater species diversity compared to small fragments. Results indicated
that the bee community within each fragment was composed of different bee species, and that species richness and diversity
increased with fragment size, although this relationship varied between the life forms. Results suggest a high degree of isolation
between fragments and greater differences in species composition. The m-dominance analysis indicated that 37% of the species recorded were restricted to medium and large-size fragments, while all
other species were randomly distributed across fragments of different size in general; ours results indicate that not only
do large fragments support greater species diversity than small fragments, but they are also essential for the conservation
of wild bee species. 相似文献
4.
茂兰喀斯特峰丛地貌森林是目前罕见的一类原生性强、人为干扰少的非地带性森林生态系统,与常态地貌地带性森林生态系统相比差异大。该研究采用典型样地调查方法对茂兰喀斯特森林海拔在620~910 m之间的垂直样带11个样方进行调查,分析研究区顶级群落物种丰富度的垂直梯度变化特征,并用冗余分析(RDA)法分析环境因子对物种丰富度的影响,以明确垂直梯度上物种丰富度与环境因子的关系,为喀斯特自然森林生态系统的维持与恢复、保护与管理提供理论基础。结果表明:(1)该调查茂兰喀斯特峰丛共记录有维管植物511种,隶属于124科272属。(2)单因素方差分析表明,该群落不同生活型的丰富度之间存在极显著差异(P<0.01);LSD多重比较分析表明,群落丰富度水平表现为总体>灌木层>草本层>乔木层。(3)随海拔梯度的升高,群落总物种丰富度和草本层物种丰富度与海拔呈显著负相关关系(P<0.05),乔木层丰富度和灌木层丰富度与海拔无明显规律。(4)冗余分析表明,土壤C/N/P的解释率达到58%,是影响物种丰富度的主要因素。 相似文献
5.
BURAK K. PEKIN ROY S. WITTKUHN MATTHIAS M. BOER CRAIG MACFARLANE PAULINE F. GRIERSON 《Austral ecology》2012,37(3):330-338
Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency. 相似文献
6.
Milan Chytrý Jiří Danihelka Irena Axmanová Jana Božková Eva Hettenbergerová Ching‐Feng Li Zuzana Rozbrojová Lucia Sekulová Lubomír Tichý Marie Vymazalová David Zelený 《植被学杂志》2010,21(6):1125-1137
Questions: Does plant species richness and composition of eastern Mediterranean dwarf shrubland (phrygana) correlate with soil pH? How important is the effect of pH on species diversity in relation to other environmental factors in this ecosystem? What is the evolutionary background of the diversity–pH relationship? Location: Western Crete, Greece. Methods: Species composition of vascular plants, soil and other environmental variables were sampled in 100‐m2 plots on acidic and basic bedrock in phrygana vegetation. The relationships between species composition and environmental variables (including climate) were tested using canonical correspondence analysis, and relationships between species richness and environment using correlation and regression analyses. Data were analysed separately for different plant functional types based on life form and life span. Results: Although soil pH varied across a narrow range (5.9‐8.1), species composition changed significantly along the pH gradient within all plant functional types. For most functional types, the effect of soil pH on species composition was stronger than that of other environmental variables. Species richness of annuals, geophytes and suffruticose chamaephytes increased with soil pH, while richness of hemicryptophytes and shrubs was not correlated with pH. Conclusions: The results are consistent with the evolutionary species pool hypothesis. High numbers of calcicole annuals, geophytes and suffruticose chamaephytes may be a result of the evolution of these groups on base‐rich dry soils in the Mediterranean climate. In contrast, hemicryptophytes, a life form typical of the temperate zone, evolved on both acidic and basic soils and therefore their species numbers do not respond to soil pH across the narrow range studied. The lack of a relationship between shrub species richness and pH is difficult to explain: it may reflect the more diverse or older origin of Mediterranean woody species and their conservative niches. 相似文献
7.
为明晰放牧强度对高寒草甸物种、生活型以及功能群多样性和生物量的时间累积作用以及对多样性与生物量之间相互关系的影响。选择青藏高原东北缘高寒草甸,在6个放牧强度样地连续4 a(2012—2015)进行物种、生活型、功能群多样性和生物量调查。采用重复测量方差分析和线性回归法分析放牧强度和放牧年份对物种、生活型、功能群多样性以及多样性与生物量之间的相关关系的影响。结果表明:(1)放牧强度和放牧年份均对生物量产生显著影响。随放牧强度增加,生物量显著降低。但随放牧年份延长,不同放牧强度区生物量无一致的变化规律。(2)放牧年份对物种、生活型和功能群丰富度、均匀度和优势度的影响均达到显著水平。但放牧强度和放牧年份只对物种丰富度产生交互作用,放牧强度对物种丰富度的影响具有时间的累积效应。(3)放牧干扰下不同层次多样性,仅物种丰富度与所有多样性指数显著相关,物种丰富度可以作为物种多样性测度的代表性指标。(4)多样性与生物量关系的研究,对丰富度而言,仅低放牧强度样地(Plot2)中物种丰富度随生物量增加而显著降低,其余放牧强度样地的物种、生活型和功能群丰富度均与生物量无关。对均匀度而言,高放牧强度样地(Plot4、Plot5、Plot6)生活型均匀度随生物量的增加而显著降低。对优势度而言,高放牧强度样地生活型优势度随生物量的增加而显著增加。生活型多样性可作为放牧干扰下生物量变化快速预测的有效指标。 相似文献
8.
Navendu V. Page Qamar Qureshi Gopal S. Rawat Cheppudira G. Kushalappa 《Plant Ecology》2010,206(2):237-250
The effect of fragmentation on different life forms within tropical forest plant communities is poorly understood. We studied
the effect of degree of fragmentation and surrounding matrix on trees, lianas, shrubs and epiphytes in tropical forest fragments
of Kodagu, Western Ghats, India. These fragments exist as sacred groves amidst a highly modified agricultural landscape, and
have been preserved by the religious sentiments of local communities. Plants were sampled at two sites in continuous forests
and 11 forest fragments. A total of 122 species of trees, 29 species of lianas, 60 species of shrubs and 66 species of epiphytes
were recorded. Trees exhibited a significant species–area relationship (R
2 = 0.74). Richness estimates after controlling for stem density (rarefaction) revealed that observed species–area relationship
was not an artefact of passive sampling. Variation in species richness of the other three groups was explained by stem density
and structural diversity. Linear distance from the reserve forest did not explain any variation in species richness. All life
forms exhibited significant nested pattern. Trees were nested along the area gradient while nestedness in the other three
groups showed evidence in support of habitat nestedness. The four life forms thus responded variably to degree of fragmentation.
Our study revealed that 74% of the regional diversity for trees was contributed by diversity among plots, highlighting the
importance of inter-patch habitat diversity in maintaining the total regional species pool. We conclude that trees alone cannot
serve as good indicator for taking appropriate conservation measures to mitigate species loss resulting from habitat fragmentation. 相似文献
9.
10.
Contrasting response of native and alien plant species richness to environmental energy and human impact along alpine elevation gradients 总被引:1,自引:0,他引:1
Lorenzo Marini Kevin J. Gaston Filippo Prosser Philip E. Hulme 《Global Ecology and Biogeography》2009,18(6):652-661
Aim We tested whether the species–energy and species–human relationships vary between native and both naturalized and casual alien species richness when other environmental variables had been taken into account. Location Trento Province, a region (c. 6200 km2) on the southern border of the European Alps (Italy), subdivided into 156 contiguous (c. 37.5 km2) cells and ranging in elevation from 66 to 3769 m. Methods Data were separated into three subsets, representing richness of natives, naturalized aliens and casual aliens and separately related to temperature, human population and various environmental correlates of plant species diversity. We applied ordinary least squares and simultaneous autoregressive regressions to identify potential contrasting responses of the three plant status subsets and hierarchical partitioning to evaluate the relative importance of the predictor variables. Results Variation in alien plant species richness along the region was almost entirely explained by temperature and human population density. The relationships were positive but strongly curvilinear. Native species richness was less strongly related to either factor but was positively related to the presence of calcareous bedrock. Native species richness had a decelerating positive relationship with temperature (R2= 55%), whereas naturalized and casual aliens had a positive accelerating relationship explaining 86% and 62% of the variation in richness, respectively. Native species richness had a positive decelerating relationship with population density (R2= 42%), whilst both alien subsets had a positive accelerating relationship. Main conclusions Alien species richness was higher in areas with the most rich and diverse assemblages of native species. Areas at high altitudes are not especially prone to alien invasion due to energy constraints, low propagule pressure and disturbance, even considering a potential increased in temperature. Thus, if we consider future environmental change, we should expect a stronger response of aliens than natives in the currently warm, urbanized, low‐altitude areas than in cold, high‐altitude areas where human population density is low. 相似文献
11.
Fabio Bulleri Lisandro Benedetti‐Cecchi Andrej Jaklin Ljiljana Ivea 《Ecology and evolution》2016,6(7):2010-2021
Biological invasions threaten biodiversity worldwide. Nonetheless, a unified theory linking disturbance and resistance to invasion through a mechanistic understanding of the changes caused to biodiversity is elusive. Building on different forms of the disturbance‐biodiversity relationship and on the Biotic Resistance Hypothesis (BRH), we constructed conceptual models showing that, according to the main biodiversity mechanism generating invasion resistance (complementary vs. identity effects), disturbance can either promote or hinder invasion. Following the Intermediate Disturbance Hypothesis (IDH), moderate levels of disturbance (either frequency or intensity) are expected to enhance species richness. This will promote invasion resistance when complementarity is more important than species identity. Negative effects of severe disturbance on invasion resistance, due to reductions in species richness, can be either overcompensated or exacerbated by species identity effects, depending on the life‐traits becoming dominant within the native species pool. Different invasion resistance scenarios are generated when the diversity‐disturbance relationship is negative or positive monotonic. Predictions from these models were experimentally tested on rocky reefs. Macroalgal canopies differing in species richness (1 vs. 2 vs. 3) and identity, were exposed to either a moderate or a severe pulse disturbance. The effects of different canopy‐forming species on the seaweed, Caulerpa cylindracea, varied from positive (Cystoseira crinita) to neutral (Cystoseira barbata) to negative (Cystoseira compressa). After 2 years, severely disturbed plots were monopolized by C. compressa and supported less C. cylindracea. Our study shows that the effects of disturbance on invasion depend upon its intensity, the main mechanism through which biodiversity generates invasion resistance and the life‐traits selected within the native species pool. Disturbance can sustain invasion resistance when promoting the dominance of competitively subordinate species possessing traits that allow outperforming invaders. 相似文献
12.
《Plant Ecology & Diversity》2013,6(4):343-351
Background: Species-rich Nardus stricta grasslands are a priority habitat for conservation in Europe. They typically occur on siliceous substrates and less frequently are found on calcareous bedrock.Aims: The present paper aimed to identify the environmental factors (i.e. bedrock type, topographic, and climatic factors) that are related with community diversity and to assess if differences in plant diversity between N. stricta communities on calcareous and siliceous bedrock occur. We hypothesised that Nardus grasslands on calcareous bedrock hosted a higher vascular plant diversity than those on siliceous bedrock.Methods: Based on 579 vegetation surveys carried out in the south-western Alps, we assessed vascular plant diversity (species richness, Shannon diversity, and Pielou’s equitability index) of species-rich Nardus grasslands and compared it between N. stricta communities on calcareous and siliceous bedrock.Results: Elevation was identified as the main factor related to species composition, while species diversity was mostly related to mean annual precipitation and bedrock type. Species richness, Shannon diversity, and Pielou’s equitability index were higher within the communities on calcareous rather than on siliceous bedrock and a total of 89 and 34 indicator species were detected, respectively.Conclusions: Based on our results, we suggest to protect primarily, as a habitat of priority interest, N. stricta grasslands on calcareous substrates for the higher vascular plant diversity hosted. 相似文献
13.
Hua-Feng Wang Xiaoting Xu Xia-Lan Cheng Yunpeng Liu Ao Luo Tong Lyu Wen-Long Wang Mir Muhammad Nizamani Zhiheng Wang 《Journal of Plant Ecology》2022,15(6):1142
Understanding large-scale patterns of biodiversity and their drivers remains central in ecology. Many hypotheses
have been proposed, including hydrothermal dynamic hypothesis, tropical niche conservatism hypothesis, Janzen’s
hypothesis and a combination model containing energy, water, seasonality and habitat heterogeneity. Yet, their
relative contributions to groups with different lifeforms and range sizes remain controversial, which have limited
our ability to understand the general mechanisms underlying species richness patterns. Here we evaluated how
lifeforms and species range sizes influenced the relative contributions of these three hypotheses to species richness
patterns of a tropical family Moraceae. The distribution data of Moraceae species at a spatial resolution of 50km
×50 km and their lifeforms (i.e. shrubs, small trees and large trees) were compiled. The species richness patterns
were estimated for the entire family, different life forms and species with different range sizes separately. The effects
of environmental variables on species richness were analyzed, and relative contributions of different hypotheses
were evaluated across life forms and species range size groups. The species richness patterns were consistent across
different species groups and the species richness was the highest in Sichuan, Guangzhou and Hainan provinces,
making these provinces the hotspots of this family. Climate seasonality is the primary factor in determining richness
variation of Moraceae. The best combination model gave the largest explanatory power for Moraceae species
richness across each group of range size and life forms followed by the hydrothermal dynamic hypothesis, Janzen’s
hypothesis and tropical niche conservatism hypothesis. All these models has a large shared effects but a low
independent effect (< 5%), except rare species. These findings suggest unique patterns and mechanisms underlying
rare species richness and provide a theoretical basis for protection of the Moraceae species in China. 相似文献
14.
Aim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition. Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W). Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data. Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition. Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships. 相似文献
15.
16.
Botanical surveys from prior to 1949 documented the plant species composition of the mulga (Acacia aneura) communities in the eastern Mulga Lands Bioregion of Queensland, Australia. These surveys recorded 282 vascular plant species
including 268 natives and 14 exotics. Since 1949, mulga communities have experienced considerable modification through continuous
grazing by domestic sheep and cattle even during drought periods and extensive vegetation clearance. To increase our knowledge
on floristic composition and diversity change over this time, floristic data were recollected from mulga communities in the
same region between 2007 and 2010 using a more systematic procedure. These surveys recorded 292 vascular plant species including
269 natives and 23 exotics. Species richness and composition within five life forms: tree, shrub, vine, forb and graminoid
were compared between the recent survey data and the historical survey data. The majority of native plant species were either
in the forb (45.4% of total native species) or graminoid (25.7% of total native species) life forms over the 60-year period.
There was no significant difference in species richness between the historical and recent surveys within tree or shrub life
forms, but there were differences in species richness in vine, forb and graminoid life forms over time. Similarities in native
species between the historical and recent surveys were high. Sorensen Similarity Indices (ISS) were: 0.77 at species level,
0.84 at genus level and 0.87 at family level. In contrast, the similarity indices for exotic species was low (0.59) for species
and genera (0.61), but high for families (0.86). More exotic species were recorded recently than historically. Among these,
buffel grass (Pennisetum ciliare) and colocynth (Citrullus colocynthis) were more commonly encountered than other exotic species in the eastern mulga communities of south central Queensland, Australia. 相似文献
17.
Species richness and cover along a 60-year chronosequence in old-fields of southeastern Spain 总被引:1,自引:1,他引:0
We analyse changes in plant cover and species richness along a 60-year chronosequence in semi-arid Mediterranean old-fields
of southeastern Spain. The objectives were: (i) to study patterns of species richness along the abandonment gradient in semi-arid
conditions (e.g., to test the “humped-back model” in our system); (ii) to test whether different broad life forms (annuals,
forbs, grasses and woody species) showed different patterns along the abandonment gradient, and (iii) to examine to what extent
plants with different dispersal strategies dominate at different stages of succession. The explained variance of the regression
relating species richness to years since abandonment is improved when considering different life forms. The results suggest
that cover and richness of different functional groups show a non-linear unimodal (often positive-skewed) pattern along the
gradient (age since abandonment). Maximum total richness is found at young stages of abandonment (<20 years), when most life
forms and dispersal strategies coexist. Annuals and perennial forbs reached their maximum richness during the first 10 years
of abandonment. About 45% of total woody species richness is reached at this time as a consequence of early colonization of
zoochorous shrubs. While the results showed a tendency towards a life-form replacement sequence, the pattern is not so clear
when looking at the different dispersal strategies. The results complement previous results in Mediterranean conditions and
emphasise the importance of considering different functional types when studying successional patterns.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
The aim of this research was to evaluate plant diversity and the relationships between the distribution of Raunkiaer life forms and community structure, and species richness, at different successional stages in communities of Quercus ilex L., Erica arborea L. and Sarcopoterium spinosum (L.) Spach., distributed as enclaves in Sinop Province. Permanent sample plots were selected to determine plant diversity. The cover percentage of each plant species was recorded monthly during two vegetation periods. Raunkiaer life forms, and the Shannon–Wiener, Evenness, Simpson and Margalef indexes were determined. Twenty-three species in Quercus ilex, 96 species in Erica arborea, and 148 species in Sarcopoterium spinosum were identified. Hemicryptophyte dominancy was observed followed by phanerophytes in the Q. ilex community, and therophyte and hemicryptophyte dominancy in the E. arborea and S. spinosum communities, respectively. It was determined that the S. spinosum community was the most heterogeneous community while the Q. ilex community was more uniform than other communities. The variation in diversity indexes, homogeneity, and composition of life forms among communities adopting a similar climatic environment could result from a differentiation of environmental factors, which impact on community structuring, from biotic to abiotic at different successional stages of Mediterranean communities. 相似文献
19.
《Plant Ecology & Diversity》2013,6(3):313-321
Background: Most studies on tropical bryophytes deal with epiphytic species. This is the first ecological study of tropical forests that focuses specifically on terrestrial bryophytes. Aim: To investigate the differences between slope and ridge environments in upper montane forests of southern Ecuador in terms of species diversity (richness, abundance), species composition and life forms of terrestrial bryophytes. Methods: We used Non-metric Multidimensional Scaling (NMDS) to group bryophyte relevés by study location, habitat type and exposure class. Species indicator values were calculated and compared for different habitats. Results: In total, 140 species were recorded, the majority being liverworts. NMDS analyses and Mantel correlations clearly separated between slope and ridge relevés, and between sunny and shaded microhabitats on ridges. Bryophyte life forms also showed different distribution patterns in slope and in ridge habitats. Mosses were more prominent in sunny than in shaded microhabitats. Conclusions: Environmental differentiation between ridges and slopes, and small-scale variation in microclimatic conditions caused by differences in exposure, were stronger predictors of species richness and composition than geographical distance between study sites. 相似文献
20.
RUTH B. RAUBER MARTA B. COLLANTES PABLO A. CIPRIOTTI JUAN ANCHORENA 《Austral ecology》2013,38(4):436-442
The biotic resistance theory relates invader success to species richness, and predicts that, as species richness increases, invasibility decreases. The relationship between invader success and richness, however, seems to be positive at large scales of analysis, determined by abiotic constraints, and it is to be expected that it is negative at small scales, because of biotic interactions. Moreover, the negative relationship at small scales would be stronger within species of the same functional group, because of having similar resource exploitation mechanisms. We studied the relationship between the cover of a worldwide invader of grasslands, Hieracium pilosella L., and species richness, species diversity and the cover of different growth forms at two different levels of analysis in 128 sites during the initial invasion process in the Fuegian steppe, Southern Patagonia, Argentina. At regional level, the invader was positively correlated to total (r = 0.28, P = 0.003), exotic (r = 0.273, P = 0.004), and native species richness (r = 0.210, P = 0.026), and to species diversity (r = 0.193, P = 0.041). At community level, we found only a weak negative correlation between H. pilosella and total richness (r = ?0.426, P = 0.079) and diversity (r = ?0.658, P = 0.063). The relationship between the invader and other species of the same growth form was positive both at regional (r = 0.484, P < 0.001) and community (r = 0.593, P = 0.012) levels. Consequently, in the period of establishment and initial expansion of this exotic species, our results support the idea that invader success is related to abiotic factors at large scales of analysis. Also, we observed a possible sign of biotic constraint at community level, although this was not related to the abundance of species of the same growth form. 相似文献