西双版纳地区小型哺乳动物群落结构及其季节变动

2008年10月—2009年6月,选择云南西双版纳地区7个不同类型生境,分别在旱季、雾凉季和雨季,采用铗夜法对小型哺乳动物群落展开调查。共布2100铗日,捕得小型哺乳动物3科10种127只,其中啮齿目(Rodentia)鼠科(Muridae)8种,食虫目(Instectivo-ra)鼩鼱科(Soricidae)和猬科(Erinaceidae)各1种,平均捕获率为6%。社鼠(Niviventer con-fucianus)是该地区小型哺乳动物群落中的优势种,其捕获率在季节之间的差异达到显著水平(P=0.023),在生境之间的差异不显著(P0.05)。在所调查的7个生境中,以生境最原始的热带雨林中的小型哺乳动物物种多样性指数最高(1.91);热带山地常绿阔叶林物种均匀度最高(0.95);热带季节性湿润林物种优势度最高(0.94)。人工橡胶林中未捕获到小型哺乳动物。3个季节中以旱季捕获小型哺乳动物数量最多。对不同生境内群落相似性指数进行聚类分析,6个生境在相似性指数0.21处全部聚合在一起。本研究结果表明,不同生境中小型哺乳动物物种多样性的丰富度与人类干扰程度有关,在人类干扰越小的生境中,小型哺乳动物种类越丰富,生物多样性指数越高;人为干扰频繁的生境物种多样性较低。     

都江堰地区小型哺乳动物群落与生境类型关系的初步研究

于2000年10月底至11月初,对都江堰地区中亚热带常绿阔叶林带不同生境类型中小型哺乳动物群落的多样性变化进行了初步研究。其捕获小型哺乳动物12种,其中啮齿目（Rodentia）鼠科（Muridae）10种,食虫目（Insce-tivora）JuQin科（Soricidae）2种,总捕获率为10.67%,在所调查的7个生境中,以干扰较轻的次生林中小型哺乳动物物种多样性指数（1.8438）和均匀度（0.9475）最高,灌丛、次生林1、原生林和弃耕地均有较高的多样性指数,农田受人类的干扰最严重,物种单一,优势度（0.5703）明显;柳杉林中的多样性指数（1.3380）和均匀度(0.8313）均较低。但原生林的物种多样性指数（1.4305）略低于次生林（1.8475和1.4610）,灌丛（1.6398）和弃耕地(1.6566）。根据不同生境内群落相似性指数进行系统聚类,7个生境在相似性指数0.0952处全部聚合在一起,灌丛、原生林和次生林中主要分布有森林型小型哺乳动物,聚为一类,为森林群落型;柳杉林和农田以大足鼠（Rattus nitidus）为优势种,聚为一类,为农田群落型;弃耕地一方面由于群落多样性指数较高（1.6566）,另一方面其农田型小型哺乳动物仍占较高比例（46.67%）,所以在聚类图中另成一类,为农林交错型。结果表明,人类活动过度干扰的生境（如农田、柳杉林）多样性指数最低,适度干扰的生境（如次生林、灌丛、弃耕地）多样性指数最高,干扰较少的生境（如原生林）多样性指数略低。     

群落结构特性的分析方法探讨-以高寒草甸和高寒灌丛为例

 从种—多度关系和物种多样性对高寒草甸和高寒灌丛在不同放牧强度下群落结构特性的分析表明,种在群落中的相对重要性发生了变化,种相对多度的分布模式符合对数正态分布,并随放牧强度的变化显示出有规律的改变;同时,表示群落结构特性的指数(Simpson多样性指数λ、Shannon信息多样性指数H′、McIntosh多样性指数Dmc、均匀性指数E和物种丰富度指数R)值在各放牧强度群落间却未表现出统计学上的显著差异(P>0.05)。这表明在有些情况下单纯对物种多样性等指数值的比较并不一定能准确地反映出群落结构上的变化,同时也证实了West关于多样性指数值保持不变或近似但群落结构可能发生变化的推断。     

放牧对沼泽化草甸土壤纤毛虫群落的影响

通过对甘南玛曲县3个不同放牧强度(全年禁牧、季节性放牧、全年放牧)的沼泽化草甸土壤纤毛虫群落研究调查,共鉴定纤毛虫105种,分别隶属于8纲、17目、30科、39属。在3种放牧强度下,季节性放牧纤毛虫物种多样性指数最高,全年禁牧次之,全年放牧最小;C/P系数(肾形类纤毛虫与多膜类纤毛虫种类数的比值)排序为季节性放牧全年禁牧全年放牧;全年禁牧和季节性放牧土壤纤毛虫的群落相似性较高,而全年放牧和全年禁牧样点之间群落差异较大。土壤含水量、有机质与物种数、密度及多样性指数呈极显著正相关(P0.01),全磷与密度呈极显著正相关(P0.01)且与物种数和物种多样性指数呈显著正相关(P0.05)。对土壤纤毛虫群落组成参数(物种数、物种多样性指数、密度)与土壤环境因子(土壤温度、含水量、pH、有机质、全氮、全磷、速效磷、无机氮)进行冗余分析,结果表明,土壤含水量、有机质、全氮对纤毛虫的群落组成影响较大,其中有机质对土壤纤毛虫群落的影响最大。     

Species turnover drives grassland community to phylogenetic clustering over long-term grazing disturbance

放牧通过改变草地群落物种组成和生物多样性,进而影响草地群落结构,对草地生态系统服务和功能产生深远的影响。然而,有关系统发育多样性和系统发育群落结构对长期放牧干扰的响应和适应的研究仍然很少,尤其是对于分布在极端环境中的生态系统。我们在青藏高原高寒草地上开展了多放牧强度的试验,探讨放牧干扰对植物系统发育多样性和群落结构的影响。研究发现,放牧干扰增加了植物群落的物种丰富度,促进了群落物种周转,从而改变了群落物种组成。低强度放牧对系统发育多样性和群落结构没有显著影响,而高强度放牧促使群落结构由分散向聚集变化。高强度放牧通过强烈的环境过滤作用,选择了一些耐牧的草地植物物种。在高强度放牧条件下,草地群落的聚集结构由近缘种的入侵和远缘种的丢失共同驱动。在植物功能性状水平上,我们发现与低强度放牧相比,高强度放牧通过改变根系深度对物种入侵产生影响,在很大程度上提升了物种的入侵性。我们的研究强调,仅仅利用物种丰富度和多样性并不能全面反映放牧干扰对草地群落的影响,而且在以后的放牧生态学研究中应该更加关注物种周转对群落系统发育多样性和群落结构的影响。     

退化草原冷蒿群落13年不同放牧强度后的植物多样性

放牧过程通过家畜的啃食、践踏干扰草原环境,使草原的物种组成发生变化,植物种群的优势地位发生更替。对退化草原中的冷蒿群落在经历13a不同放牧强度——无牧（0．00只羊,hm^2）、轻牧（1．33只羊／hm^2）、中牧（4．00只羊／hm^2）、重牧（6．67只羊,hm^2）的围栏放牧后的植物群落多样性进行研究,结果表明：经过13a的演替变化,（1）无牧处理下植被密度显著低于其它3个放牧处理下的植被密度,而其它3个放牧处理之间的植被密度差异不显著;（2）无牧处理下羊草成为群落的优势种,轻牧和中牧处理下冷蒿依然是群落的优势种。这3种处理下寸草苔的种群密度最大;重牧处理下优势种变为星毛委陵菜,并且其种群密度最大;随着放牧强度增加,不同放牧退化阶段指示植物的种群密度的变化趋势是：冷蒿为先增大后减小,而星毛委陵菜为先急剧增大,然后平缓增大,最后再急剧增大;（3）植物多样性和均匀度指数在中牧处理下最大,在无牧处理下最小,说明中牧处理下群落的多样性最高,无牧处理下群落的多样性最小。而优势度指数正相反。植物群落结构和多样性的变化主要是由放牧家畜选择性采食、不同植物对放牧响应的不同策略、植物种间的竞争、动植物协同进化以及由放牧改变的土壤理化性质等因素综合决定的。此研究有助于进一步认识退化草原在继续放牧干扰下的演替规律以及为退化草原的保护和恢复提供理论依据。     

放牧强度对短花针茅荒漠草原甲虫群落分布格局的影响

放牧对脆弱的荒漠草原生态系统有着重要影响,且随放牧强度及持续时间不同而变化。鞘翅目昆虫是环境监测与生物多样性变化的指示生物。利用巴氏罐诱法对短花针茅荒漠草原不同放牧强度草地的甲虫群落组成和多样性进行调查,探究放牧对荒漠草原甲虫群落的影响。结果表明:(1)步甲科、金龟科为短花针茅荒漠草原甲虫群落优势类群,埋葬甲科、芫菁科、拟步甲科和花金龟科为常见类群。(2)放牧强度增加不利于维持更多的捕食性甲虫;对照和轻度放牧样地可维持更多的腐食性甲虫。(3)甲虫数量随放牧强度增加而递减;群落多样性以重度放牧草地最大,轻度放牧草地最小;群落优势度为对照、中度、重度显著高于轻度放牧草地。各甲虫类群在不同放牧强度草地出现时间、高峰期均不同。(4)对照、轻度、重度放牧样地的甲虫优势类群群落结构不同于其他生境,但均与中度放牧样地存在相似性。轻度、中度、重度放牧样地的甲虫稀有类群群落结构不同于其他生境,但均与对照样地存在相似性。(5)甲虫群落个体数与植物群落物种丰富度、盖度、植物平均高度、生物量呈显著正相关。Shannon-Wiener多样性指数、Margalef丰富度指数均与植物群落物种丰富度、生物量显著负相关。研究结果为荒漠草原甲虫多样性保护提供参考依据。     

小兴安岭林区不同生境梯度中小型哺乳动物生物多样性

利用铗日法和陷阱法,于2000年7～8月,对小兴安岭林区7个不同生境梯度中小型哺乳动物群落的多样性变化进行了初步研究。结果表明：(1)铗日法所捕获的物种数和个体数明显大于陷阱法．但后者更适合捕获小体型动物;(2)共捕获小型哺乳动物9种．其中啮齿目(Rodentia)松鼠科(Sciuridae)1种．田鼠亚科(Microtine)3种．鼠科(Muridae)4种．食虫目(Insectivora)鼩鲭科(Soricidae)1种．所捕获的物种中．棕背解(Clethrionomys rufocanus)为优势种．占总数的48．77％．与黑线姬鼠(Apodemus agrarius )、大林姬鼠(A．speciosus)和红背Ping(C．rutilus)一起构成本地区的常见种;(3)物种在不同的生境类型中呈明显的不均匀分布．以中度干扰的灌丛生境内小型哺乳动物从物种丰富度和多样性指数最高．次生林1和农田生境均有较高的物种丰富度和多样性指数,无干扰的原生林1、2中物种丰富度最低,而轻微干扰的原生林3中物种多样性指数最低．受严重干扰的农田生境中小型哺乳动物均匀度最高．其次是次生林1和灌丛,原生林3和干扰较重的次生林2中小型哺乳动物群落均匀度最小;(4)从物种多样性与林地郁闭度和地表草本植物覆盖度的相关分析看出：物种多样性与郁闭度相关性不显著．而与覆盖度呈显著的正相关关系．反映了这些物种对草本植物选择倾向;(5)根据不同生境内群落相似性指数进行系统聚类,将所有的生境聚类为3组．即原生林组(原生林1、原生林2和原生林3)、次生林组(次生林1和次生林2)和农田组(灌丛和农田)．表明组内各生境间小型哺乳动物成分的相似性和组间的明显差异。研究表明．小型哺乳动物多样性受生境内植被演替阶段、食物和隐蔽条件等环境因素影响．而人类干扰也是主要因素之一。     

不同干扰形式对砂生槐群落结构特征的影响

在雅鲁藏布江中游流域以放牧、封育和水淹3种不同干扰形式下的砂生槐群落为研究对象,从林分特征、物种组成、优势种种群发育状况和物种多样性等对群落特征进行对比研究,以揭示不同干扰形式对砂生槐群落结构的影响.结果显示:(1)砂生槐群落以群落A(放牧)的林分状况最好,其次为群落B(封育),群落C(水淹)最差;(2)不同干扰形式下群落中植物种类分别为群落A(13种)＞群落C(9种)＞群落B(6种);(3)优势种群生长状况说明放牧和封育形式下砂生槐生长情况基本一致,高度级和幅度级小的个体均较多,而水淹干扰下群落仅有少数生长旺盛的个体存在,种群呈衰退趋势;(4)物种多样性指数为群落A＞群落B＞群落C.研究表明:一定程度放牧干扰能够促进砂生槐种群更新,增加群落物种丰富度和物种多样性,封育可促进砂生槐种群萌蘖更新,而水淹则促使群落衰退.     

牦牛放牧率对小嵩草高寒草甸暖季草场植物群落组成和植物多样性的影响

两年的牦牛放牧试验结果表明:在暖季草场,随着放牧率的提高,禾草和莎草类功能群的盖度、生物量及其组成与高度减小,它们与放牧率呈显著的负相关 P<0.05 可食杂草和毒杂草类功能群的盖度、生物量及其组成与高度增加,它们与放牧率呈显著的正相关 P<0.05 各功能群的盖度与生物量之间是显著的正相关关系 P<0.05 .对照草地由于没有牦牛的采食,群落由少数优势种植物所统治,群落结构趋于简单,物种组成贫乏,物种多样性和均匀度指数最小;轻度放牧牦牛选择采食对植物群落的影响较小,群落的物种丰富度指数、均匀度指数和多样性指数均不高;中度放牧提高了资源的利用效率,增加了群落结构的复杂性,草地的物种丰富度指数、均匀度指数和多样性指数均最高,该结果支持 中度干扰理论 ;重度放牧由于牦牛采食过于频繁,改变了植物的竞争能力,导致植物种的均匀度下降,多样性减少.不同放牧率草地群落的物种数 S 、丰富度指数 Ma 、多样性指数 Shan-non-Wiener指数H′和Simpson指数D 、均匀度指数 Pielow指数J′ 的排序为:对照<轻度放牧<重度放牧<中度放牧,优势度指数 Berger-Parke指数 的变化趋势则与之相反.     

Grazing response groups among understorey plants in arid rangelands

Abstract. We analysed attributes of the understorey flora in different plant communities along two grazing gradients in arid Australian rangelands. We aimed to determine if there were patterns among species in response to grazing, and easily recognizable ‘indicator response types’ for monitoring grazing-induced change in community composition. Measurements were stratified by vegetation patch type, in woody groves and open patches. Trait selection and analyses followed a hierarchical approach which searched for patterns within major plant life forms. Patch type exerted a dominant influence on both life forms and species attributes, but interacted with grazing. Grazing was associated with loss in differentiation of species composition between patch types, rather than loss in numbers of species overall. Heavy grazing was variously associated with small size, prostrate habit, low meristems, small leaves, coated leaves, high regrowth potential, plasticity in response to grazing, and high fecundity; and light grazing with opposing attributes. Many attributes tended to vary independently of each other and grazing-related attribute syndromes were recognisable only among grasses. This could be because the environmental filters acting on the communities have given rise to many different species with different natural attribute combinations, few of which are closely associated with grazing resistance. For grassy communities ‘large, erect tussocks branching above-ground’ and ‘small, sprawling basal tussocks’ may have potential as response types indicative of light and heavy grazing respectively, but no response types could be identified for herbaceous communities.     

Long-Term Grazing Accelerated Litter Decomposition in Northern Temperate Grasslands

Livestock grazing affects plant community composition, diversity, and carbon (C) and nutrient cycling in grasslands. Grazing leads to plant communities that have higher relative abundance of grazing-tolerant species, which in turn may alter the chemical composition of biomass and subsequent litter decomposition rates. To better understand the effects of long-term grazing and associated vegetation shifts on biogeochemical cycling in northern temperate grasslands of western Canada, we studied litter decomposition over 18 months at 15 locations, stratified across the Mixed-grass Prairie, Central Parkland, and Foothills Fescue natural subregions. At each location, we examined decomposition in an area exposed to grazing and an area where cattle were excluded. We used litterbags containing leaf litter from seven major grass species representing different grazing tolerances and included a local source of community litter from each study site and cellulose paper as standards. Decomposition was affected by litter types, with litter from grazing-tolerant species such as Poa pratensis and Bouteloua gracilis having faster decomposition rates compared to grazing-intolerant species, supporting the hypothesis that changes in vegetation composition due to grazing influences biogeochemical cycling by modifying litter decomposition in grasslands. Litter decomposition was also overall most rapid in the cool–wet Foothills Fescue, followed by the temperate mesic Central Parkland, and slowest in the warmer–drier Mixed-grass Prairie. Combined with known grazing-induced changes in grassland composition, these findings indicate that livestock grazing may accelerate litter decomposition rates in the more mesic Foothills Fescue and parkland regions, but not the more arid Mixed-grass Prairie. Overall, this study elucidates the role of livestock grazing and its associated effects on litter decomposition and ecosystem processes in northern grassland ecosystems.     

Regional productivity mediates the effects of grazing disturbance on plant cover and patch‐size distribution in arid and semi‐arid communities

Patch‐size distribution and plant cover are strongly associated to arid ecosystem functioning and may be a warning signal for the onset of desertification under changes in disturbance regimes. However, the interaction between regional productivity level and human‐induced disturbance regime as drivers for vegetation structure and dynamics remain poorly studied. We studied grazing disturbance effects on plant cover and patchiness in three plant communities located along a regional productivity gradient in Patagonia (Argentina): a semi‐desert (low‐productivity community), a shrub‐grass steppe (intermediate‐productivity community) and a grass steppe (high‐productivity community). We sampled paddocks with different sheep grazing pressure (continuous disturbance gradients) in all three communities. In each paddock, the presence or absence of perennial vegetation was recorded every 10 cm along a 50 m transect. Grazing effects on vegetation structure depended on the community and its association to the regional productivity. Grazing decreased total plant cover while increasing both the frequency of small patches and the inter‐patch distance in all communities. However, the size of these effects was the greatest in the high‐productivity community. Dominant species responses to grazing explained vegetation patch‐ and inter‐patch‐size distribution patterns. As productivity decreases, dominant species showed a higher degree of grazing resistance, probably because traits of species adapted to high aridity allow them to resist herbivore disturbance. In conclusion, our findings suggest that regional productivity mediates grazing disturbance impacts on vegetation mosaic. The changes within the same range of grazing pressure have higher effects on communities found in environments with higher productivity, markedly promoting their desertification. Understanding the complex interactions between environmental aridity and human‐induced disturbances is a key aspect for maintaining patchiness structure and dynamics, which has important implications for drylands management.     

Desertification,no‐change or alternative states: Can we trust simple models on livestock impact in dry rangelands?

Abstract. It is remarkable that after many thousands of years of pastoralism in arid and semi‐arid savannas, there is still no clear answer to the basic question: Does livestock grazing have more than a marginal effect on the dynamics of arid and semi‐arid land vegetation? A small study of semi‐arid savanna vegetation along a spatial gradient in grazing pressure, repeated three times over 19 years is used as a basis for discussing the behaviour of dry land vegetation under heavy grazing. Three basic theories are compared: (1) the theory that heavy grazing causes desertification; (2) the theory that heavy grazing causes no directed change in the vegetation of arid and semi‐arid rangelands; and (3) the theory that heavy grazing leads to a switch between alternative states of vegetation. On the basis of the current data the first two theories are rejected, but the conclusion is that there is much evidence for a more complex behaviour of dry rangelands under grazing than what is accommodated in any of the three theories. Probably, site‐specific properties including interactive and indirect effects of herbivory in the system are important for vegetation development under grazing in arid and semi‐arid rangelands.     

Are plant functional types relevant to describe degradation in arid,southern Tunisian steppes?

Abstract. In the Tunisian arid zone disturbances (e.g. overgrazing and agriculture) and stresses (e.g. aridity, low fertility) drive changes in the structure and functioning of rangelands, with a decrease in perennial plant cover, changes in floristic composition and erosion. Long‐term monitoring requires (1) an understanding of the dynamics of vegetation change and associated ecological processes and (2) identification of relevant indicators. Using data from the arid zone of southern Tunisia we tested the hypothesis that plant functional response types could be used to address these two goals. We identified plant functional response types in response to a gradient of soil and vegetation types characterized by changes in perennial plant cover, dominant species and associated soil types. Vegetation samples were stratified by contrasted vegetation patch types with varying perennial plant cover (1.6 to 22%). We focused our analysis of trait responses within dwarf–shrubs, which are the dominants in typical steppe ecosystems of south Tunisia. Available trait data concerned morphology (plant height, leaf type), regeneration (dispersal mode, phenology and regeneration mode) and grazing value. Although we found it difficult to recognize ‘indicator response types’ that could be used directly to monitor changes in community composition, we were able to identify plant response syndromes that are relevant to long‐term vegetation changes, and in particular degradation processes, in the region. Two main response types were identified: the decreaser type, made up of small or medium chamaephytes with high grazing palatability and the increaser type with medium to tall chamaephytes and low grazing palatability. These response types are proposed as key elements in a state‐and‐transition model of vegetation dynamics in the context of agropastoral disturbances and climatic and edaphic stresses.     

Response of soil bacterial communities to moisture and grazing in the Tibetan alpine steppes on a small spatial scale

As the Third Pole of the world, the Tibetan Plateau provides a typical alpine grassland environment for soil bacteria with its unique frigid and arid climate. Owing to clear changes in spatial moisture and increased grazing intensity, moisture and livestock grazing have become key factors influencing the microbial communities. Accordingly, we investigated the diversity and composition of soil bacteria in a selected alpine grassland within the dual gradients of moisture and grazing using high-throughput sequencing. Our results showed that grazing changed the soil bacterial diversity and composition, whereas moisture only influenced the relative abundance of the segmental community at the small spatial scale. Species richness was found to be increased by moderate grazing compared with that by high or low-grazing intensity. The relative abundance of dominant species and β-diversity of soil bacteria both showed differences with heavy, moderate, and low grazing. Some dominant bacteria were altered with the moisture content. However, there were no significant differences according to the moisture gradient in terms of the overall bacterial β diversity and composition. These results might be taken account into the small spatial scale as well as the compensation of grazing to moisture on this scale. This work provides new insights into the soil bacterial response to moisture gradients and grazing intensity in alpine steppe habitat.     

Identifying trends in land degradation in non-equilibrium rangelands

1. Change in environmental conditions in the complex non-equilibrium rangelands of arid Australia is difficult to monitor. We show how trends in rangeland condition can be identified from changes over time in the pattern of vegetation growth across gradients of differing grazing intensity.
2. Grazing intensity was measured indirectly using distance from water. Vegetation growth was derived from remotely sensed vegetation index values before and after large rainfalls. The amount of growth was adjusted for initial vegetation cover to give a standard measure of vegetation response.
3. A vegetation response ratio was derived by comparing areas less than 4 km from water with benchmark areas further away. Systematic changes in this ratio over time indicate a trend.
4. Ratio values from test areas suggested decline, improvement and no change, consistent with recent management history.
5. The method can be applied where the whole area is affected by grazing and relatively pristine benchmarks are unavailable. It could therefore be useful in the semi-arid rangelands where paddocks are smaller than in the arid part of Australia. It also has possible uses in the rangelands of Africa and the Americas. There is potential for applying the method to traditional grazing systems as well as to commercial pastoralism.
6. The method is cheaper and more effective than other techniques and increases the capacity of grazing gradient-based monitoring schemes for arid and semi-arid areas.     

Grazing as a factor structuring grasslands in the Pyrenees

Questions: What are the relative roles of abiotic and grazing management factors on plant community distribution in landscapes? How are livestock type and stocking rate related to changes in vegetation structure and composition? Location: Sub‐alpine grasslands in the central and eastern Pyrenees. Methods: Multivariate analysis and variance partitioning methods were used to evaluate the relative roles of environmental factors in structuring vegetation composition and diversity patterns in three surveys on differently managed grasslands. Results: Vegetation composition within a region was affected by environmental factors hierarchically, changing first according to abiotic factors and then to grazing management. At landscape scales, abiotic factors explained two‐fold more variation in vegetation composition than grazing factors. Within landscape units, cattle grazing increased vegetation heterogeneity at landscape and patch scales, while sheep grazing favoured the presence of a specific set of species with high conservation value. Species composition was highly responsive to management variables compared to diversity components. Conclusions: The combination of sheep and cattle grazing at various stocking rates is an effective tool to preserve the diversity of plant species and communities within a region with a long tradition of livestock management, through the scaling up of effects by local processes occurring in patches at smaller scales.     

Small mammalian herbivore determines vegetation response to patchy nutrient inputs

Nutrient inputs to plant communities are often spatially heterogeneous, for example those deriving from the dung and urine of large grazing animals. The effect of such localised elevation of nutrients on plant growth and composition has been shown to be modified by the grazing of large herbivores. However, there has been little work on interactions between small mammalian herbivores and such patchy nutrient inputs, even though these interactions are potentially of major significance for plant performance and community structure.
We examined the effect of simulated cattle urine deposition on the vegetation structure, above-ground biomass and species composition of chalk grassland within enriched patches. Short-term exclosures were used to determine whether a small herbivore (rabbit) would preferentially graze the vegetation in enriched patches and what impact this interaction would have on the performance of plants in such patches. Rabbit grazing pressure determined whether nutrient inputs had a negative or positive effect on plant biomass. Nutrients increased plant biomass in the absence of grazing, but when exposed to grazing, plants in nutrient-rich patches had more biomass consumed by herbivores than neighbouring plants. Further, nutrients increased the relative palatability of a less preferred forage species ( Brachypodium pinnatum ), contributing to changes in plant community composition. We conclude that a small herbivore can drive plant responses to patchily distributed nutrients.     

Cattle grazing, raptor abundance and small mammal communities in Mediterranean grasslands

Abundance and diversity of small mammals are usually affected strongly by grazing either due to decreased food availability or quality, decreased suitability of soil for building burrow systems due to trampling and/or due to increased predation risk in the structurally simpler grazed areas. We estimated the effects of grazing-induced changes in vegetation and soil and of increased predation on small mammals in a Mediterranean grassland landscape. We measured vegetation structure, soil compaction and small mammal abundance and species composition in 22 plots of 8 Sherman live traps each, arranged according to an unbalanced two-way ANOVA design with two grazing levels (grazed areas and cattle exclosures) and two predator abundance levels (increased densities of Eurasian kestrels Falco tinnunculus by means of nest boxes and control). Plots were sampled during 2 consecutive years in early summer and early fall. Exclosure from cattle increased significantly vegetation height and volume and decreased soil compaction. Grazing-induced changes in vegetation height and volume and in soil compaction produced strong effects on small mammal abundance and species richness. Increased kestrel densities did not have significant additive or interactive effects, with the effects of grazing-induced vegetation and soil gradients on abundance or richness of small mammals. Our results suggest that the effects of grazing on small mammal communities in Mediterranean montane grasslands were mainly due to reduced food availability and by negative effects of trampling on the suitability of soils for building burrow systems. Decreased food quality and increased predation in grazed areas seemed to play a minor role, if any. Reductions in stock densities would then favor generalist predator populations in Mediterranean grasslands through the expected positive effects of such reductions on the availability of food and burrows for small mammals.