Analizando la diversidad vegetal en dos áreas de contrastado efecto de Herbívoros invasores en la isla de Tenerife.

Plant - Invertebrate Interactions in Agriculturally Managed Grasslands Under Functional Group Manipulation

Because the quantity, quality, and heterogeneity of resources should affect the diversity of consumers, plant productivity, plant composition, and plant diversity may influence the diversity of trophic levels higher up the food chain (bottom-up control of diversity). Increasing plant productivity may increase herbivore diversity by: increasing the abundance of rare resources (resource rarity hypothesis), increasing herbivore abun- dance and local persistence (consumer rarity hypothesis) or increasing intraspecific den- sity dependence (density dependence hypothesis). Increasing plant diversity may increase the diversity of herbivores because herbivores specialized on these new plant species can persist locally. Increasing the diversity of herbivores could likewise increase the diversity of predators and parasites, although parasite and predator diversity may also respond directly to changes in vegetation. Here I use data from a well-replicated grassland experiment at Cedar Creek, Minnesota, to analyze the responses of arthropod diversity to independent manipulations of (1) plant productivity and (2) plant diversity and composition. Long-term nitrogen addition (historical treatment) decreased plant diversity and favored C3 grasses. Short-term nitrogen addition (modern treatment) increased plant productivity without appreciably changing plant diversity or plant composition. Arthropods were sampled using both sweep nets and vacuum samplers. Total arthropod species richness and abundance, as well as species richness and abun- dance of every trophic group (detritivores, herbivores, parasites, and predators), were sig- nificantly greater in plots with higher levels of modern fertilization and greater plant pro- ductivity. Path analysis supported the consumer rarity hypothesis, because modern fertil- ization increased herbivore species richness only indirectly by increasing herbivore abun- dance. Surprisingly, higher levels of historical fertilization that lowered plant species richness (but did not change plant productivity) significantly increased total arthropod species richness, did not affect detritivore or herbivore species richness, and significantly increased parasite and predator species richness. Direct and indirect effects of historical fertilization on the species richness of trophic groups were separated statistically using block regression chain modeling. Herbivore species richness was decreased through the direct pathway, but this was offset through indirect effects so that there was no overall response to historical fertilization. In plots with low plant diversity, similar numbers of herbivore species supported a greater diversity of parasites and predators. These results suggest that the diversity and composition of plants control the diversity of consumers not only directly by determining available resources, but also indirectly by influencing the interactions between herbivores and their parasites and predators.

Aim Urbanization is associated with strong changes in biodiversity, but the diversity of plant and animal assemblages varies among urban habitats. We studied effects of urban habitats on the diversity of vascular plants and land snails in 32 large cities. Location Central Europe, Belgium and the Netherlands. Methods The species composition of all vascular plants that had not been planted by humans, and all land snails, was recorded in seven 1-ha plots within each city. Each plot contained one urban habitat type representing a different disturbance regime: historical city square, boulevard, residential area with compact building pattern, residential area with open building pattern, park, early successional and mid-successional site. For each plot, we obtained temperature and precipitation data. The effects of climate and habitat types on species composition were quantified using ordination methods with an adjusted variation partitioning algorithm. Differences in species composition among urban habitats were described using statistically determined diagnostic species, and differences in alpha, beta and gamma diversity were quantified. Results A total of 1196 plant and 87 snail species were recorded. Habitat type explained higher proportions of the total variation in both plant and snail species composition (11.2 and 8.2%, respectively) than did climate (4.6 and 6.3%). For both taxa, the main differences in species composition were observed between strongly urbanized sites in city centres and early successional and mid-successional sites. For vascular plants, the number of species was lowest in city squares and boulevards, and highest at successional sites and in residential areas with compact building patterns. Beta diversity of vascular plants calculated for the same habitat types among cities was highest for squares and successional sites. The number of snail species was lowest in city squares and at early successional sites, and highest at mid-successional sites. The highest beta diversity of snail assemblages among cities was observed within the city square and early successional habitat types, and the lowest within residential area habitat types. Main conclusions Urban habitats differ notably in the diversity of their vascular plant flora and land snail fauna. Understanding the habitat-related biodiversity patterns in urbanized landscapes will allow projections of future impacts of urban land-use changes on the biota.

Because the quantity, quality, and heterogeneity of resources should affect the diversity of consumers, plant productivity, plant composition, and plant diversity may influence the diversity of trophic levels higher up the food chain (''bottom-up'' control of diversity). Increasing plant productivity may increase herbivore diversity by: increasing the abundance of rare resources (''resource rarity hypothesis''), increasing herbivore abun- dance and local persistence (''consumer rarity hypothesis'') or increasing intraspecific den- sity dependence (''density dependence hypothesis''). Increasing plant diversity may increase the diversity of herbivores because herbivores specialized on these new plant species can persist locally. Increasing the diversity of herbivores could likewise increase the diversity of predators and parasites, although parasite and predator diversity may also respond directly to changes in vegetation. Here I use data from a well-replicated grassland experiment at Cedar Creek, Minnesota, to analyze the responses of arthropod diversity to independent manipulations of (1) plant productivity and (2) plant diversity and composition. Long-term nitrogen addition (''historical treatment'') decreased plant diversity and favored C 3 grasses. Short-term nitrogen addition (''modern treatment'') increased plant productivity without appreciably changing plant diversity or plant composition. Arthropods were sampled using both sweep nets and vacuum samplers. Total arthropod species richness and abundance, as well as species richness and abun- dance of every trophic group (detritivores, herbivores, parasites, and predators), were sig- nificantly greater in plots with higher levels of modern fertilization and greater plant pro- ductivity. Path analysis supported the consumer rarity hypothesis, because modern fertil- ization increased herbivore species richness only indirectly by increasing herbivore abun- dance. Surprisingly, higher levels of historical fertilization that lowered plant species richness (but did not change plant productivity) significantly increased total arthropod species richness, did not affect detritivore or herbivore species richness, and significantly increased parasite and predator species richness. Direct and indirect effects of historical fertilization on the species richness of trophic groups were separated statistically using block regression chain modeling. Herbivore species richness was decreased through the direct pathway, but this was offset through indirect effects so that there was no overall response to historical fertilization. In plots with low plant diversity, similar numbers of herbivore species supported a greater diversity of parasites and predators. These results suggest that the diversity and composition of plants control the diversity of consumers not only directly by determining available resources, but also indirectly by influencing the interactions between herbivores and their parasites and predators.

Summary It is well documented that large herbivores have pronounced effects on plant communities in grassland ecosystems, and the extent and course of their effects can largely depend on both plant and herbivore characteristics. Previous studies highlighted the importance of plant productivity in predicting the impact of herbivores on grasslands. Yet, there has been little consideration of how different herbivores affect plant communities that, in turn, differ in plant diversity. In a 2‐year grazing experiment, we tested the effects of large herbivores (cattle or sheep, or both together) on plant communities under high and low plant diversity levels in eastern Eurasian steppe. We found that, for high plant diversity grassland, mixed grazing by cattle and sheep significantly increases plant diversity, but we found no effect of grazing by cattle or sheep alone. Grazing by cattle or sheep alone or mixed grazing by cattle and sheep did not significantly affect plant biomass in the high diversity grassland. However, for low plant diversity grassland, grazing by cattle alone and mixed grazing by cattle and sheep significantly increased plant diversity, but significantly decreased plant biomass. There was no significant impact on both plant diversity and biomass from sheep grazing. Synthesis and applications. We conclude that the effects of grazing in grassland strongly depend on herbivore assemblages and pre‐grazing plant diversity. Herbivore grazing might contribute more to the maintenance of grassland structure and ecosystem functioning under high plant diversity compared with low plant diversity. Furthermore, our data suggest that multiple‐species mixed grazing regimes in grassland systems with high plant diversity could represent the optimal protocol for grazing management. This study emphasizes the importance of maintaining both plant and herbivore diversity to optimize ecosystem functioning.

Summary The interactions between adjacent trophic levels are essential for ecosystem functioning and stability. Grazing by domestic herbivores is an essential interaction in grasslands, but little information is available on the nature of relationship between plant and insect diversity under grazing by large herbivores. We examined the effects of large herbivores on the relationship between plant and insect diversity with five grazing treatments (control, cattle, goat, sheep and a mixture of the three grazing types) across three plant diversity levels (low: 4–5 species, intermediate: 8–9 species and high: 15–17 species) in a meadow steppe. We found that the grazing treatments did not significantly affect plant species richness, but reduced plant biomass, plant height and cover. Grazers affected variation in plant height differently at different plant diversity levels, and this variation increased at the low plant diversity level and decreased at the high plant diversity level after grazing. A similar pattern was observed for insect species richness: grazing had a positive impact at the low plant diversity level, but had a negative impact at the high plant diversity level. In the absence of grazing, insect species richness was positively associated with plant species richness, but it decreased with increasing plant diversity in the grazing treatments. This was attributed to strong responses of insect species richness to plant height heterogeneity under grazing by large herbivores, implying that plant structural heterogeneity is more important than plant diversity in influencing insect diversity in grazed grasslands. Synthesis and applications. Grazing by large herbivores may reverse the positive relationship between plant diversity and insect diversity by modifying plant structural heterogeneity. Therefore, the spatial heterogeneity of vegetation structure should be given more attention in future work on plant–insect interactions. This study further highlights the importance of using large herbivore grazing in management actions, not only to maintain diversity but also to mediate trophic interactions in grasslands.

Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity.

The ecosystems around, and plant composition in, paddy fields in Java are varied, owing to differences in climate, altitude, and traditional farming practice. This study examines the effects of different types of surrounding land use and vegetation on the plant diversity in paddy fields. We studied three upland (400–850 m asl) and three lowland areas (10–50 m asl) in the island of Java, Indonesia. Samples of vegetation were taken in fields and bunds (partition between paddy field plots) in two rice cultivation seasons from October 2011 through to June 2012, including the peak of rice cultivation in Java between October and February. We used Analysis of Variance Matrix Unbalanced to analyze the effects of area, complexity, location, and season on plant composition. Tukey’s Honestly Significant Difference (HSD) test was performed to determine significant differences between groups in the sample. We recorded 14 crop species and 221 non-cultivated plant species, of which 171 species occurred in paddy fields and 190 on bunds. Species numbers in upland areas were higher than in lowland areas. In fallows, twice as many species as in cultivated rice fields were found. The presence of semi-natural vegetation within short distance had no significant effect on plant species numbers in paddy fields. Multiple cropping and intercropping around paddy fields and on bunds had a marked effect on plant diversity. Differences in plant species numbers and composition between lowland and upland areas are more pronounced than the effects of local environmental complexity. To enhance high and varied plant diversity on the field and landscape scale, traditional multiple and intercropping systems should be supported.

Grassland plant community structure and function are dependent on the type, timing, frequency and intensity of disturbance. Grazing systems employing dense herds of livestock for short periods of time (e.g. Adaptive Multi‐paddock Grazing; AMP) are gaining popularity as a potentially sustainable practice. Effects of AMP systems on plant diversity and composition are unknown, though theory provides some expectations. Spatially homogeneous grazing used by AMP may be a uniform ecological filter, thereby lowering plant diversity; alternatively, the AMP practice of using multiple paddocks might enhance habitat heterogeneity. Maintaining plant diversity, particularly of native species, is a key aspect of sustainability. As such, an understanding of the real‐world effects of AMP grazing is needed. We studied grasslands within 18 pairs of ranches across the northern Great Plains. Ranches managed under AMP were paired with a neighbouring ranch (N‐AMP) using regionally representative grazing practices. We collected surveys of management practices and conducted 2 years of on‐farm sampling to identify plant composition and diversity. Ranch management practices used by self‐identified AMP ranchers differed significantly (p < 0.1) from those used on neighbouring ranches, with higher stocking densities (number of animals per area at a single time) but not stocking rates (total number of animals per unit time per area) on AMP relative to N‐AMP ranches. There were fewer plant species in AMP grasslands at both the plot and landscape scales compared to N‐AMP ranches despite no overall difference in plant community composition. Management type did not alter the variability of plant community composition (beta diversity) or plot‐level species evenness. Although there were trends for lower diversity of native and introduced species at both spatial scales, a significant effect was found only for native species at the landscape scale. Synthesis and applications. The impacts of AMP grazing system management were limited to a minor reduction in plant diversity, with a modest decline in native species richness. We conclude that the benefits of AMP grazing in the northern Great Plains do not include the maintenance of plant diversity, and this system could hinder the conservation of remaining native plant species.

Plant-diversity hotspots on a global scale are well established, but smaller local hotspots within these must be identified for effective conservation of plants at the global and local scales. We used the distributions of endemic and endemic-threatened species of Myrtaceae to indicate areas of plant diversity and conservation importance within the Atlantic coastal forests (Mata Atlântica) of Brazil. We applied 3 simple, inexpensive geographic information system (GIS) techniques to a herbarium specimen database: predictive species-distribution modeling (Maxent); complementarity analysis (DIVA-GIS); and mapping of herbarium specimen collection locations. We also considered collecting intensity, which is an inherent limitation of use of natural history records for biodiversity studies. Two separate areas of endemism were evident: the Serra do Mar mountain range from Paraná to Rio de Janeiro and the coastal forests of northern Espírito Santo and southern Bahia. We identified 12 areas of approximately 35 km(2) each as priority areas for conservation. These areas had the highest species richness and were highly threatened by urban and agricultural expansion. Observed species occurrences, species occurrences predicted from the model, and results of our complementarity analysis were congruent in identifying those areas with the most endemic species. These areas were then prioritized for conservation importance by comparing ecological data for each.

Field ridges are commonly viewed as the stable semi-natural habitats for maintaining plant diversity in the agricultural landscape. The high plant diversity could further support higher animal diversity. But following the adoption of well-facilitated farmland construction measures in China, many field ridges have been disproportionately neglected or destroyed. Empirical studies delineating the relationships between plant and animal diversity in these field ridges in the paddy landscape remain scant, especially in China, which has the most rice production. A two-year field ridge evaluation was conducted in the Chengdu Plain area, covering 30 paddy landscapes. This investigation scrutinizes the shape attributes of field ridges, their plant diversity, and the associated animal α-diversity and community compositions, including spiders, carabids, birds, frogs, and rice planthoppers. In the results of Pearson's correlation analysis, a significant inconsistent correlation was observed between plant diversity and animal diversity. The analysis of community structure heterogeneity also revealed no correspondence for species composition between plant and animal communities (i.e., spiders, carabids, and birds), while the non-metric multidimensional scale analysis indicated a substantial difference in the species composition of spiders or plants even within the same field ridge between 2020 and 2021. We argue that the implementation of intensive management practices in paddy landscapes, such as machine ploughing and harvesting and herbicide spraying with drones, leads to a scarcity of stable animal and plant communities in field ridges. Therefore, besides retaining these field ridges in paddy landscapes, maintaining the long-term stable ridges by refraining from herbicide spraying or artificial weeding, as well as avoiding winter wheat cultivating in field ridges, will contribute to protecting biodiversity of field ridges as semi-natural habitats.

Traditional homegardens (HGs) are considered to harbor high levels of plant diversity and have been therefore characterized as sustainable agro-ecosystems suitable for on-farm (incl. circa situm) conservation of plant genetic resources. While the functional structure of traditional HGs is poorly understood specifically for semi-arid and arid regions, their plant species richness and diversity is increasingly threatened by recent and fast evolving agricultural transformation processes. This has been particularly claimed for traditional jubraka HG systems of Sudan. Therefore, sixty-one HGs in four villages of the Nuba Mountains, South-Kordofan Province, Sudan, were randomly selected, geographically recorded and plant richness and abundance determined and plant diversity parameters calculated. In addition, socio-economic household data were assessed by interviews and soil samples taken to allow a comprehensive analysis of putative factors affecting HG plant diversity across different villages, levels of commercialization and plant species composition based clusters. A total of 110 species from 35 plant families were grown in the HGs along with 71 ornamentals. Perennial species accounted for 57 % including 12 indigenous fruit tree (IFT) species and six exotic fruit tree species. Mean species richness of useful plant species (excluding ornamentals) per HG was 23 (range 6–46). On average, 41 % of the 23 species per HG were of exotic origin, however, with a large range (21–83 %) among locations. Mean diversity and evenness indices were 1.46 (range 0.49–2.42) and 0.48 (0.15–0.87), respectively. The level of commercialization of HGs only marginally affected species diversity measures although the species richness was significantly higher for commercial than subsistence HGs. Species richness was higher on lower (6.6–7.2) pH soils. IFT richness was highly variable, but non-significantly different across the four locations. Plant species richness and diversity was high in comparison with other HG systems in semi-arid regions. Cluster analysis was found to be a valuable tool to classify HGs and to extract homogeneous HG types with low, intermediate and high richness and diversity. In addition, the share of exotic and ornamental species in HGs indicated a trend towards the loss of traditional farming practices, particularly in areas with good market access. The data did not indicate the hypothesized loss of inter-specific diversity due to commercialization and species richness was numerically even higher for market-oriented HGs compared to subsistence ones.

Simultaneous reductions in herbivore abundance and increases in nitrogen deposition have led to radical shifts in plant communities worldwide. While the individual impacts of these human‐caused disturbances are apparent, few studies manipulate both herbivory and N, nor differentiate among herbivore guilds, to understand contingencies in the ability of these drivers to affect producer diversity and productivity. As such, understanding how the main and combined effects of increasing soil N with declining herbivores may influence plant community structure and function is critical to better understand the future of grassland ecosystems under multiple global change drivers.In this study, we asked: (a) What are the main effects of small mammal herbivores, invertebrate herbivores, and soil N on plant community structure and function? and (b) Are the effects of invertebrate herbivores and soil N on plant community structure and function contingent on small mammal herbivory? We used a nested design, with invertebrate and soil N treatments nested within small mammal manipulations in an existing tallgrass prairie. We measured plant community structure by quantifying plant richness, evenness, diversity, and composition across two full growing seasons. We also recorded total aboveground biomass to quantify grassland productivity.We found that small mammal herbivores strongly shaped plant diversity, species composition, and productivity. Small mammal herbivores also mediated the effects of soil N and invertebrate herbivores on grassland community structure, but not composition or productivity. Small mammal reduction lowered plant species richness while increasing aboveground biomass and altering compositional similarity. Invertebrate herbivores, in the presence of small mammals, promoted plant dominance by reducing evenness without altering compositional similarity. Additionally, soil nitrogen addition reduced plant richness, but only when small mammals were reduced, and no effects were detected on compositional similarity or productivity.Our findings provide further evidence that temperate grasslands can be strongly influenced by consumers, and that consumers mediate the effects of resources as well as other consumer guilds on producer evenness and richness. Taken together, we provide evidence of strong contingencies in the drivers of grassland structure, with small mammals directly altering plant diversity as well as mediating the effects of soil nitrogen and invertebrate herbivory on plant richness and evenness. Therefore, we suggest it is imperative to consider how consumer guilds and resource types may interact to shape grassland plant communities.

Bioenergy from perennial grasses mitigates climate change via displacing fossil fuels and storing atmospheric CO2 belowground as soil carbon. Here, we conduct a critical review to examine whether increasing plant diversity in bioenergy grassland systems can further increase their climate change mitigation potential. We find that compared with highly productive monocultures, diverse mixtures tend to produce as great or greater yields. In particular, there is strong evidence that legume addition improves yield, in some cases equivalent to mineral nitrogen fertilization at 33–150 kg per ha. Plant diversity can also promote soil carbon storage in the long term, reduce soil N2O emissions by 30%–40%, and suppress weed invasion, hence reducing herbicide use. These potential benefits of plant diversity translate to 50%–65% greater life-cycle greenhouse gas savings for biofuels from more diverse grassland biomass grown on degraded soils. In addition, there is growing evidence that plant diversity can accelerate land restoration. Bioenergy from perennial grasses mitigates climate change via displacing fossil fuels and storing atmospheric CO2 belowground as soil carbon. Here, we conduct a critical review to examine whether increasing plant diversity in bioenergy grassland systems can further increase their climate change mitigation potential. We find that compared with highly productive monocultures, diverse mixtures tend to produce as great or greater yields. In particular, there is strong evidence that legume addition improves yield, in some cases equivalent to mineral nitrogen fertilization at 33–150 kg per ha. Plant diversity can also promote soil carbon storage in the long term, reduce soil N2O emissions by 30%–40%, and suppress weed invasion, hence reducing herbicide use. These potential benefits of plant diversity translate to 50%–65% greater life-cycle greenhouse gas savings for biofuels from more diverse grassland biomass grown on degraded soils. In addition, there is growing evidence that plant diversity can accelerate land restoration.

1. How herbivore plant diversity relationships are shaped by the interplay of biotic and abiotic environmental variables is only partly understood. For instance, plant diversity is commonly assumed to determine abundance and richness of associated specialist herbivores. However, this relationship can be altered when environmental variables such as temperature covary with plant diversity.2. Using gall‐inducing arthropods as focal organisms, biotic and abiotic environmental variables were tested for their relevance to specialist herbivores and their relationship to host plants. In particular, the hypothesis that abundance and richness of gall‐inducing arthropods increase with plant richness was addressed. Additionally, the study asked whether communities of gall‐inducing arthropods match the communities of their host plants.3. Neither abundance nor species richness of gall‐inducing arthropods was correlated with plant richness or any other of the tested environmental variables. Instead, the number of gall species found per plant decreased with plant richness. This indicates that processes of associational resistance may explain the specialised plant herbivore relationship in our study.4. Community composition of gall‐inducing arthropods matched host plant communities. In specialised plant herbivore relationships, the presence of obligate host plant species is a prerequisite for the occurrence of its herbivores.5. It is concluded that the abiotic environment may only play an indirect role in shaping specialist herbivore communities. Instead, the occurrence of specialist herbivore communities might be best explained by plant species composition. Thus, plant species identity should be considered when aiming to understand the processes that shape diversity patterns of specialist herbivores.