Aspects of the ecology of Patella spp. on the Portuguese coast

Three species of the genus Patella were studied on the Portuguese coast as a specific contribution to the COST 647 programme. With little prior information existing, this paper presents new basic data on the geographical distribution, relative abundance, habitats, size-structure of populations, and reproductive cycles of P. depressa Pennant, 1777, P. aspera Roding, 1798, and P. vulgata L. 1758. Comparisons with N.W. Europe provide evidence of distinct latitudinal trends in the population dynamics and reproductive biology of these species.     

Diets and resource partitioning between larvae of three anisopteran species

Analysis of resource partitioning between larvae of three Anisopteran species showed that Aeshna cyanea and Anax imperator (both Aeshnidae) tended to occupy similar ecological niches which were not shared by Libellula depressa (Libellulidae).The diets of these predators and comparisons between trophic availability and diets indicated that prey species eaten varied according to season and predator species, and that some selection of prey species occurred.     

The ability of several high arctic plant species to utilize nitrate nitrogen under field conditions

The ability to utilize NO _inf3 ^sup– in seven high arctic plant species from Truelove Lowland, Devon Island, Canada was investigated, using an in vivo assay of maximum potential nitrate reductase (NR) activity and applications of ¹⁵N. Plant species were selected on the basis of being characteristic of nutrient-poor and nutrient-rich habitats. In all species leaves were the dominant site of NR activity. Root NR activity was negligible in all species except Saxifraga cernua. NO _inf3 ^sup– availability per se did not appear to limit NR activity of the species typically found on nutrient-poor sites (Dryas integrifolia, Saxifraga oppositifolia, and Salix arctica), or in Cerastium alpinum, as leaf NR activities remained low, even after NO _inf3 ^sup– addition. ¹⁵NO _inf3 ^sup– uptake was limited in D. integrifolia and Salix arctica. However, the lack of field induction of NR activity in C. alpinum and Saxifraga oppositifolia was not due to restricted nitrate uptake, as ¹⁵NO _inf3 ^sup– labelled NO _inf3 ^sup– entered the roots and shoots of both species. Leaf NR activity rates were low in three of the species typical of nutrient-rich habitats (O. digyna, P. radicatum and Saxifraga cernua), sampled from a site containing low soil NO _inf3 ^sup– . Additions of NO _inf3 ^sup– significantly increased leaf NR activity in these latter species, suggesting that potential NR activity was limited by the availability of NO _inf3 ^sup– . ¹⁵N labelled NO _inf3 ^sup– was taken up by O. digyna. P. radicatum and Saxifraga cernua. Although two species (D. integrifolia and Salix arctica) showed little utilization of NO _inf3 ^sup– , we concluded that five of the seven selected high arctic plant species (C. alpinum, O. digyna, P. radicatum, Saxifraga cernua and Saxifraga oppositifolia) do have the potential to utilize NO _inf3 ^sup– as a nitrogen source under field conditions, with the highest potential to utilize NO _inf3 ^sup– occurring in three of the species typically found on fertile habitats.     

Silurian Leptaeninae (Brachiopoda) from Gotland, Sweden

Strophomenid brachiopods belonging to the generaLeptaena andLepidoleptaena are described from the uppermost Llandovery — Ludlow succession of Gotland, Sweden. In Gotland,Lepidoleptaena comprises the single speciesL. poulseni, andLeptaena includes four species:L. rhomboidalis, L. sperion, L. depressa andL. parvirugata n. sp.L. depressa shows a considerable amount of morphological variation, which is recognised in the two new subspeciesLeptaena depressa visbyensis n. ssp. from the Llandoverian — Wenlockian Visby Formation, andL. depressa lata n. ssp. from the mid-Wenlockian Slite Group. The distribution of the different species is largely substrate-dependent, withLeptaena rhomboidalis andLepidoleptaena poulseni adapted to high-energy environments with firm substrates, whereas the remaining species preferred fine-grained substrates in low-energy environments.      

Ecological correlates of invasion by <Emphasis Type="Italic">Arundo donax</Emphasis> in three southern California riparian habitats

Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature, incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies also suggests that a high degree of environmental tolerance contributes to invasion success.     

Species-specific patterns of hydraulic lift in co-occurring adult trees and grasses in a sandhill community

Plants can significantly affect ecosystem water balance by hydraulic redistribution (HR) from dry to wet soil layers via roots (also called hydraulic lift, HL, when the redistribution is from deep to shallow soil). However, the information on how co-occurring species in natural habitats differ in HL ability is insufficient. In a field study, we compared HL ability of four tree species (including three congeneric oak species) and two C4 bunch grass species that co-occur in subxeric habitats of fall-line sandhills in southeastern USA. Soil water potentials (_s) were recorded hourly for 3 years both in large chambers that isolated roots for each species and outside the chambers. Outside of root chambers, soil drying occurred periodically in the top 25 cm and corresponded with lack of precipitation during the summer growing season. Soil moisture was continuously available at a 1 m depth. HL activity was observed in three of the tree species, with greater frequency for Pinus palustris than for Quercus laevis and Q. incana. The fourth tree species Q. margaretta did not exhibit HL activity even though it experienced a similar _s gradient. For the C4 bunch grasses, Aristida stricta exhibited a small amount of HL activity, but Schizachyrium scoparium did not. The capacity for HL activity may be linked to the species ecological distribution. The four species that exhibited HL activity in this subxeric habitat are also dominant in adjacent xeric sandhill habitats, whereas the species that did not exhibit HL are scarcely found in the xeric areas. This is consistent with other studies that found greater fine root survival in dry soil for the four xeric species exhibiting HL activity. The differential ability of these species to redistribute water from the deep soil to the rapidly drying shallow soil likely has a strong effect on the water balance of sandhill plant communities, and is likely linked to their differential distribution across edaphic gradients.An erratum to this article can be found at     

扎龙湿地不同生境芦苇功能性状变异及其对土壤因子的响应

物种的遗传特征和外在环境条件的差异共同决定了植物功能性状的表达,植物功能性状可以反映物种对环境条件的适应策略。采用大样本抽样调查与统计分析方法,比较研究扎龙湿地4种生境（盐碱生境、旱生生境、湿生生境和水生生境）芦苇分株和叶功能性状,分析不同生境芦苇功能性状的分异规律及其对土壤因子的响应。结果表明：（1）不同生境芦苇功能性状均表现出中等程度变异。其中分株和叶性状均以盐碱生境最低（P<0.05）,分株及除叶面积和比叶面积以外的叶性状均以水生生境最高;株高和株重在种群内的变异系数为15.96%-48.61%和38.65%-87.82%,种群间的变异系数为46.58%和66.39%;叶性状在种群内的变异系数为13.21%-72.37%,种群间的变异系数为26.46%-57.03%;（2）不同生境芦苇功能性状间存在协同变化特征。芦苇的株高、株重、叶长、叶宽、叶面积和叶重之间均呈极显著正相关关系（P<0.01）,比叶面积与其他性状的相关性因生境不同存在一定变化;（3）不同生境芦苇的原位土壤因子表现出异质性特征,芦苇功能性状的变异是含水量、pH、有机质和速效氮等土壤因子综合作用的结果。其中含水量、有机质和速效氮为正向驱动,而pH为负向驱动。因此,芦苇通过自我调节功能性状更好地适应不同的生存环境,局域尺度不同生境的土壤因子是引起芦苇功能性状产生分异的导因。     

不同盐渍化生境野生乌拉尔甘草土壤细菌群落结构及功能预测分析

【目的】探究典型盐生药用植物野生乌拉尔甘草在不同盐渍化生境下土壤细菌群落多样性、组成和功能特征,有助于建立土壤盐分与甘草生长发育、药材品质形成相关的微生物组之间的联系,对栽培甘草药材品质提高具有重要意义。【方法】从野生乌拉尔甘草的6个主分布区采集原生境土壤,采用高通量测序技术比较非盐渍(un-salinization, US)、轻度盐渍(light salinization, LS)、中度盐渍(moderate salinization, MS)以及重度盐渍(heavy salinization, HS)生境中土壤细菌群落多样性、组成及功能的差异,并挖掘不同生境中优势细菌。【结果】野生乌拉尔甘草原生境土壤细菌群落丰富度和多样性在轻度盐渍(LS)组和中度盐渍(MS)组中明显高于非盐渍(US)组、重度盐渍(HS)组,且重度盐渍(HS)组最低。主成分分析(principal component analysis, PCA)表明不同盐渍程度组间的野生乌拉尔甘草土壤细菌群落组成和功能具有显著差异(P<0.05);冗余分析(redundancy analysis, RDA)表明,土壤盐分(total salt, TS)既是影响原生境土壤细菌群落组成也是影响群落功能的重要因子。属水平,非盐渍(US)组和轻度盐渍(LS)组中的显著优势细菌相同,均为植物有益菌,包括类诺卡氏菌属(Nocardioides)、链霉菌属(Streptomyces)、栖大理石菌属(Marmoricola);重度盐渍(MS)组中显著优势属既包括有益菌未鉴定_酸杆菌属(unidentified_Acidobacteria),也包括嗜盐菌盐单胞菌属(Halomonas)、海杆菌属(Marinobacter);重度盐渍(HS)组中显著优势细菌以嗜盐菌或耐盐菌为主,包括盐单胞菌属(Halomonas)、海杆菌属(Marinobacter)、楚帕氏菌属(Truepera)、别样矿生菌属(Aliifodinibius)、盐坑微菌属(Salinimicrobium)和需盐杆菌属(Salegentibacter)。PICRUSt功能预测分析强调非盐渍(US)组、轻度盐渍(LS)组和中度盐渍(MS)组中的土壤细菌群落与植物互作方面的潜力,表明非盐渍、轻度盐渍和中度盐渍生境中的有益菌对野生乌拉尔甘草生长发育、品质形成具有重要影响。PICRUSt功能预测同时也强调了重度盐渍(HS)组在自我修复适应高盐环境以及参与野生乌拉尔甘草耐盐性提高方面具有潜能,表明重度盐渍生境中的嗜盐菌和耐盐菌对乌拉尔甘草抗盐能力具有重要作用。中度盐渍生境兼具以上二者优势菌群的特征,是值得关注的类型。【结论】野生乌拉尔甘草土壤细菌群落多样性和丰富度在轻度盐渍和中度盐渍生境中明显高于非盐渍和重度盐渍生境;细菌群落的组成和功能在非盐渍和轻度盐渍生境中具有相似性,并与重度盐渍生境存在显著差异,中度盐渍生境兼具以上二者的特征。     

山地虎耳草和棒腺虎耳草转录组SSR和SNP分析

利用Illumina HiSeqTM2000对山地虎耳草和棒腺虎耳草进行转录组测序,分析和比较其SSR和SNP特征。结果表明:山地虎耳草63 763条Unigene序列中含有4 622个SSR,发生频率为7.25%,有110种重复基元,平均每10.00kb出现一个SSR位点;棒腺虎耳草60 972条Unigene序列中含有4 542个SSR,发生频率为7.45%,有85种重复基元,平均每10.40kb出现一个SSR位点,略低于山地虎耳草。山地虎耳草和棒腺虎耳草转录组序列的SSR优势基元均为三核苷酸重复。2个物种的转录组SSR以5~10次的较低重复次数为主,长度主要集中于12~30bp,具有较高的多态性。山地虎耳草和棒腺虎耳草中分别获得118 424个和112 006个SNP位点,编码区的SNP位点分别占30.40%和28.59%,且在编码SNP中同义突变所占比例(30.27%、28.48%)远高于非同义突变(0.13%、0.11%)。比较发现,2个物种的各项检索结果基本一致,推测与选取的组织部位、组织的发育阶段以及物种的亲缘关系有关。     

Physiological integration helps a clonal macrophyte spread into competitive environments and coexist with other species

Physiological integration may help clonal macrophytes invade or escape from existing communities. No studies have tested the above hypothesis in aquatic plants. In an outdoor pond experiment, we subjected clonal fragments of the submerged macrophyte Vallisneria spiralis L. to heterogeneous environments in which V. spiralis spread from bare habitats towards vegetated habitats occupied by Myriophyllum spicatum L. or V. spiralis spread from vegetated habitats towards bare habitats. V. spiralis stolons between ramets in bare habitats and in vegetated habitats were either intact or severed. We investigated the habitat selection of V. spiralis by examining the allocation of biomass and ramets to heterogeneous habitats during its vegetative spread phase. Results showed that the stolon connection had different effects on the habitat selection of V. spiralis with regard to invasion and escape. When V. spiralis spread from bare to vegetated habitats, in comparison to severing the stolon, the stolon connection eventually facilitated a 49% increase in biomass and a 27% increase in number of ramets allocated to vegetated habitats. However, when V. spiralis spread from vegetated to bare habitats, biomass and ramets allocated to bare habitats were not significantly changed by the stolon connection (only a 5% increase in biomass and a 6% increase in number of ramets). These results indicate that clonal integration facilitated V. spiralis not to escape from but invade into vegetated habitats. The study provides evidence that physiological integration is important for survival and tolerance of ramets in competitively stressful environments and can help clonal macrophytes coexist with other species.     

Do natural container habitats impede invader dominance? Predator-mediated coexistence of invasive and native container-dwelling mosquitoes

Predator-mediated coexistence of competitors occurs when a species that is superior in competition is also more vulnerable to a shared predator compared to a poorer competitor. The invasive mosquito Aedes albopictus is usually competitively superior to Ochlerotatus triseriatus. Among second instar larvae, A. albopictus show a lesser degree of behavioral modification in response to water-borne cues from predation by the larval midge Corethrella appendiculata than do O. triseriatus, rendering A. albopictus more vulnerable to predation by C. appendiculata than O. triseriatus. The hypothesis that C. appendiculata predation favors coexistence of these competitors predicts that C. appendiculata abundances will be negatively and positively correlated with A. albopictus and O. triseriatus abundances, respectively, and that coexistence will occur where C. appendiculata are common. Actual abundances of O. triseriatus, A. albopictus, and C. appendiculata in three habitats fit this prediction. In natural container habitats like tree holes, C. appendiculata were abundant and competitors co-existed at similar densities. In cemeteries and tires, which occur primarily in non-forested, human-dominated habitats, A. albopictus dominated, with abundances twice those found in tree holes, but C. appendiculata and O. triseriatus were rare or absent. We also tested for whether antipredatory behavioral responses of A. albopictus differed among habitats or populations, or were correlated with local C. appendiculata abundances. We could detect no differences in A. albopictus antipredatory behavioral responses to water-borne cues from predation. Tree hole habitats appear to promote co-existence of O. triseriatus and A. albopictus through interactions with predatory C. appendiculata, and this predator effect appears to limit invasion success of A. albopictus in tree holes. There are many studies on predator-mediated coexistence in natural habitats but to our knowledge this is the first study to suggest differential predator-mediated coexistence between natural and man-made habitats. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ecological significance of light controlled seed germination in two contrasting tropical habitats

Summary The effects of temperature, photoperiod, phytochrome photoreversion and the response to a R/FR ratio gradient were investigated in seeds of four species from two contrasting tropical habitats; two species from a rain forest (Cecropia obtusifolia and Piper umbellatum) and two from a high altitude lava field covered by low vegetation (Buddleja cordata and Chenopodium ambrosioides). In the rain forest seed species the photoblastic response seems to be adapted to light quality changes due to canopy destruction, on the other hand, the lava field seed species seem to be adapted to instantaneous light stimulus such as would be produced by the sudden exposure of a buried seed to the soil surface light environment.     

Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.     

不同生境下假臭草生长特征分析

通过测定庄稼地、弃耕地、桉树林、公路边4种生境下假臭草叶面积(LA)、比叶面积(SLA)、LDMC和株高等形态特征、植株各构件生物量及生物量分配比和假臭草种群盖度、密度等种群数量性状,研究不同生境类型下假臭草个体的形态特征、生物量及生物量分配和种群生长状况的差异。结果表明:光照和土壤养分对假臭草的形态特征、生物量及生物量分配和种群数量性状的影响显著;低光照、高土壤养分生境下假臭草的LA、SLA、株高较高,假臭草叶片的LDMC较小,植株的花序数较少,生物量主要向叶和茎器官进行分配,根和花果器官的生物量分配则受到限制;高光照、养分贫瘠生境下假臭草的LA、SLA、株高较低,假臭草叶片的LDMC较大,生物量主要向根和花果器官进行分配,种群的盖度、密度、生物量和高度等种群数量性状较低,种群生长状况较差;高光照、肥沃养分生境为假臭草的最适生境,假臭草构件的资源配置较为优化,株高、基径粗、冠宽和花序数等形态指标较大,种群盖度、密度、生物量等种群数量性状较大,种群生长较好。     

石灰土和酸性土生境下金花茶组植物叶片钙形态差异

为探究不同生境下金花茶组植物的叶片钙形态特征，该研究以10种石灰土生境和4种酸性土生境的金花茶为对象，测定了其生境土壤的钙含量和pH值，以及该生境下金花茶组植物叶中的硝酸钙和氯化钙、水溶性有机酸钙、果胶酸钙、磷酸钙和碳酸钙、草酸钙、硅酸钙和总钙的含量。结果表明：(1)石灰土生境的土壤钙含量和土壤pH均极显著(P<0.01)高于酸性土。(2)在石灰土生境中，金花茶组植物的叶钙形态以草酸钙(41.17%)为主，而在酸性土生境中则以果胶酸钙(43.10%)为主，除硝酸钙和氯化钙、果胶酸钙外，石灰土金花茶的各叶钙形态和总钙含量均极显著(P<0.01)高于酸性土金花茶。(3)相关性分析结果显示，大部分叶钙形态含量与土壤pH和土壤钙含量呈极显著(P<0.01)正相关，表明土壤环境对金花茶组植物叶钙形态特征具有重要影响。(4)单因素方差分析结果显示，各叶钙形态含量在物种间存在极显著(P<0.01)差异，表明金花茶组植物在物种分化过程中叶钙形态特征具有多样性。(5)基于叶钙形态特征的聚类分析显示，14种金花茶可归为3大类。总体而言，不同生境背景下金花茶组植物的叶钙形态差异可能是...     

Seed weight increases with altitude in the Swiss Alps between related species but not among populations of individual species

Seed weight is a crucial plant life history trait, determining establishment success and dispersal ability. Especially in stressful environments, larger seeds may be selected at the expense of seed number, because larger seeds have a better chance of giving rise to an established offspring. We tested the hypotheses that between related species-pairs and among populations of single species a similar trend for increasing seed weight with increasing altitude should be present. Firstly, we measured seed weights from 29 species-pairs, with one species occurring in lowland areas and a congeneric species from high altitudes. Seeds of the alpine species were 28±8% larger than seeds from lowland species (P<0.01). Compared to the related lowland species, 55% of the alpine species had heavier seeds, 3% (one species) had lighter, and 41% had seeds of approximately equal weight. Secondly, we compared seed weights among populations of four species from different habitats and with different life histories. Seeds from between 11 and 34 populations per species were sampled along altitudinal gradients of 800–1,500 m (ca. 800 m in Scabiosa lucida, ca. 1,000 m in Saxifraga oppositifolia, ca. 1,000 m in Epilobium fleischeri, and ca. 1,500 m in Carex flacca). In all the four species, we found no indication for heavier seeds at higher altitudes. Our results indicate a selection pressure for species with heavier seeds at higher altitude, but the trend does not seem to operate across all cases. Phylogenetic constraints may limit the correlation among altitude and seed weight, operating particularly against selection for larger seed size, the closer populations and species are related to each other.     

水菜花种群潜在生境选择与空间格局预测

国家二级保护野生植物水菜花(Ottelia cordata)，喜生于清洁的水环境中，对环境变化极为敏感，是检验湿地环境及气候变化的关键指示物种之一，在我国仅零星分布于海南北部的火山熔岩湿地区，生存状况不容乐观。研究水菜花种群潜在生境选择及其空间格局演变，有利于加强濒危物种保护保育及湿地生态系统修复、管理。该研究基于GIS平台和MaxEnt模型，结合气候、地形和土壤因子，探究水菜花种群环境限制因子及其在气候变化背景下潜在适宜生境的演变格局。结果表明，水菜花种群对温差与降水量变化敏感，等温性、最冷季度降水量、土壤类型和年均降水量对水菜花种群分布影响显著；全新世中期-当前-2070年气候变化背景下，水菜花适宜生境面积先减小后增大，分布重心呈西南-东北-西南转移格局；未来气候情景下，水菜花种群高度和中度适宜生境缩减，低适宜生境增加，南部地区将出现新增适宜生境，东北、西北及西南部适宜生境将发生消减。该研究从气候环境角度论证了水菜花种群的潜在生境选择及空间变化特征，可为濒危物种保护保育、湿地管理及其生物多样性维护工作提供参考和指导。     

Spatial and Temporal Dynamics of Exotic Earthworm Communities Along Invasion Fronts in a Temperate Hardwood Forest in South-Central New York (USA)

The invasion of North American forests by exotic earthworms is producing profound ecosystem changes, such as alterations in soil nutrient cycling, and redistribution and loss of soil organic matter. However, the present and future extent of these invasions is difficult to evaluate without a better understanding of the factors that control the distribution and abundance of earthworms in previously non-invaded habitats. In this study, the species composition and short-term dynamics of three exotic earthworm invasion fronts were studied at a northern hardwood forest in south-central New York State (USA). Belt transects were established at each of the three locations to sample from earthworm-invaded areas through transition zones and into invasion front areas. Lumbricus rubellus, L. terrestrisandOctolasion tyrtaeum were the most common species, but their distribution was not homogeneous along the transects. Whereas, L. rubellus was the only species with relatively high adult densities at transition zones and invasion fronts, L. terrestris and O. tyrtaeum occurred mostly in the heavily earthworm-invaded areas and were rare at the invasion fronts. The density of earthworms along the transects decreased by 60–87 from June 2001 to October 2002 and then recovered in 2003 to values similar to those of 2001. This decrease was apparently caused by reduced recruitment of immature earthworms, probably related to the severe drought periods that the study area experienced in 2001 and 2002. Our data suggest that climate and topography, through their effects on soil moisture patterns, can be critical factors controlling the distribution and spread of exotic earthworms in previously non-invaded habitats.