Invasive Grass Species Research Articles

Evidence of phytotoxicity in a fast-growing shrub useful for savanna restoration in Central Brazil

Finding fast-growing native species able to interfere in invasive grass species’ growth is essential to restore savannas and grasslands, where native tree growth is rather limited. We tested the phytotoxicity of Lepidaploa aurea (Mart. ex DC.) H.Rob. (Asteraceae), a native shrub from the Brazilian savanna that apparently inhibits the growth of invasive grasses in degraded areas and in areas under restoration process. We performed experiments in Petri dishes and soil conditions using four receiver species: three eudicots: Lactuca sativa L., Raphanus sativus L., Solanum lycopersicum L. and a monocot: Sorghum bicolor L. Moench. These are model species commonly used in phytotoxic studies for their known germination rates and high sensitivity to allelochemicals. We tested the effects of aqueous extracts of L. aurea’s leaves and roots, in four concentrations (10, 5, 2.5, 1.25%) and a control (distilled water). We performed tests in natural versus sterilized soils to identify the influence of soil microbiota in L. aurea’s phytotoxicity. We found phytotoxic effects in all tested conditions. Leaf extracts had more accentuated negative effects on target plants than did root extracts. The growth of receiver plants’ root was more affected than shoot growth. Lepidaploa aurea can be an important ally for the restoration of degraded areas savannas and grasslands. Studies considering species that co-occur with L. aurea in conserved and disturbed are as are necessary to confirm this allelopathic potential.

Reproductive biology of Sorghum halepense (L.) Pers. (Poaceae; Panicoideae; Andropogoneae) in relation to invasibility

Sorghum halepense (L.) Pers. is the most aggressive grass weed of the world resulting from an efficient system of its reproduction and propagation through a combination of vegetative and sexual means. However, reproductive biology of the species is not understood in sufficient details and had serious gaps of information on its pollen and pollination system, breeding behaviour, fruit and dispersal biology. The species was found to be chasmogamous with an andromonoecious sexual system of well-developed bisexual and male spikelets in pairs and terminal triads. Precocious extrusion of receptive stigmas preceding anther dehiscence, abundant pollen of high fertility and longevity and a high pollen-ovule ratio strongly indicate xenogamy in the species. Laser Confocal Microscopy revealed rapid germination of pollen and growth of pollen tubes down the pistil to the ovule which caused high fruit set and facilitated the amphimictic cycle. The present study is presumably the first report on the role of several insect pollinators mainly from the order Diptera (Isomyia paurogonita Fang & Fan.) and Hymenoptera (Hylaeus sp., Sphecodes ephippius Linnaeus , Megachile sp.). The visitation time of insect pollinators closely synchronized with peak anthesis resulting in high pollen loads. Breeding experiments revealed significantly higher fruit set in open pollinated in comparison to bagged synflorescences. The diaspore enclosed a well-developed caryopsis surrounded by accessory bracts along with persistent pedicels and a rachis segment preparing them for dispersal through autochory and endozoochory. Thus, cosmopolitan and invasive nature of S. halepense could be attributed to a combination of xenogamous breeding system, high seed production and efficient fruit dispersal through resistant diaspores. This study on the reproductive system of S. halepense shall provide a framework for developing management strategies both for the control of this invasive grass species as also for its propagation as a fodder crop in vacant rangelands.

Arthropod and oligochaete assemblages from grasslands of the southern Kenai Peninsula, Alaska.

BackgroundBy the end of this century, the potential climate-biome of the southern Kenai Peninsula is forecasted to change from transitional boreal forest to prairie and grasslands, a scenario that may already be playing out in the Caribou Hills region. Here, spruce (Picea × lutzii Little [glauca × sitchensis]) forests were heavily thinned by an outbreak of the spruce bark beetle (Dendroctonus rufipennis (Kirby, 1837)) and replaced by the native but invasive grass species, Calamagrostis canadensis (Michx.) P. Beauv. As part of a project designed to delimit and characterize potentially expanding grasslands in this region, we sought to characterize the arthropod and earthworm communities of these grasslands.We also used this sampling effort as a trial of applying high-throughput sequencing metabarcoding methods to a real-world inventory of terrestrial arthropods.New informationWe documented 131 occurrences of 67 native arthropod species at ten sites, characterizing the arthropod fauna of these grasslands as being dominated by Hemiptera (60% of total reads) and Diptera (38% of total reads). We found a single exotic earthworm species, Dendrobaena octaedra (Savigny, 1826), at 30% of sites and one unidentified enchytraeid at a single site. The utility of high-throughput sequencing metabarcoding as a tool for bioassessment of terrestrial arthropod assemblages was confirmed.

Ergot species of the Claviceps purpurea group from South Africa

Results of a survey and study of the Claviceps purpurea group of species in South Africa are being presented and five new species are described. Morphological descriptions are based on the anamorphs and four nuclear genetic loci. Claviceps fimbristylidis sp. nov. on Fimbristylis complanata was discovered wide-spread across five provinces of the country associated with water and represents the fourth Claviceps species recorded from the Cyperaceae. Claviceps monticola sp. nov. is described from Brachypodium flexum growing in mountain forests in Mpumalanga Province, as well as the northern Drakensberg southwards into the Eastern Cape Province. Claviceps pazoutovae sp. nov. is recorded from Stipa dregeana var. dregeana and Ehrharta erecta var. erecta, also associated with these mountain ranges. Claviceps macroura sp. nov. is recorded from Cenchrus macrourus from the Eastern Cape and Claviceps capensis sp. nov. from Ehrharta villosa var. villosa is recorded from the Western Cape Province. Claviceps cyperi, only recorded from South Africa is included in the study. Ergot alkaloid profiles of all species are provided and showed similarity to C. purpurea. Only C. cyperi and in lesser degree C. capensis, C. macroura, and C. pazoutovae produced ergot alkaloids in clinically significant amounts. Several reported species infect invasive grass species, native to South Africa, and thus represent potentially invasive species.

Propagule quality mediates invasive plant establishment

Propagule pressure is commonly considered a primary driver of invasive plant establishment and spread. However, the physical size or condition (i.e., quality) of propagules may also affect establishment, particularly under unfavorable habitat conditions such as low light environments. We used an outdoor mesocosm experiment to test the relative contribution of propagule size (number of individuals introduced) and quality (number of rhizome nodes) to the establishment and performance of the highly invasive cogongrass (Imperata cylindrica) under experimental sun and shade treatments. We found that the introduction of higher quality propagules (rhizome segments ≥3 nodes in length) significantly enhanced establishment across both light treatments, and increased final tiller count in the sun treatment. The sun treatment also enhanced rhizome growth, an effect that could increase spread rates and invasion success. Thus, while cogongrass is likely to establish in both sun and shade, introductions of large propagule sizes or large rhizomes in high light environments likely poses the greatest threat to native habitats. Our results demonstrate that propagule quality promoted both establishment and performance of a highly invasive grass species and suggest that propagule quality may play an important but underappreciated role in the invasion process.

Evolutionary responses of invasive grass species to variation in precipitation and soil nitrogen

SummaryGlobal climate models suggest that many ecosystems will experience reduced precipitation over the next century and the consequences for invasive plant performance are largely unknown. Annual invasive species may be able to quickly evolve traits associated with drought escape or tolerance through rapid genetic changes.We investigated the influence of 5 years of water and nitrogen manipulations on trait values in a southern California grassland system. Seeds from two annual grass species (Avena barbataandBromus madritensis) were collected from experimental plots and grown in a common environment over two generations. We measured 14 physiological, morphological, phenological and reproductive traits.Both species displayed phenotypic differences depending on the water treatment from which they were collected, but not depending on the nitrogen treatment. Both species displayed trait values characteristic of drought escape (e.g. earlier flowering inA. barbataandB. madritensis, lower water‐use efficiency inB. madritensis) when grown from the seeds collected from plots that experienced five years of reduced precipitation. Furthermore,A. barbataindividuals grown from the seeds collected from drought plots had higher reproductive output and higher photosynthetic performance than individuals grown from water addition plots, with individuals grown from ambient plots displaying intermediate trait values. Notably, we found no phenotypic variation among treatments for six root traits.Synthesis. Trait differences were observed following two generations in a common garden, suggesting that treatment differences were genetically based. This suggests that populations were responding to selection over the 5 years of water manipulations, a remarkably short time period. The rapid evolutionary responses observed here may help these two widespread invasive grass species thrive under reduced precipitation scenarios, which could have important implications for fire dynamics, invasive species management and native plant restoration in communities invaded by annual grasses.

Long-Term Fire Effects on Native and Invasive Grasses in Protected Area Sagebrush Steppe

Following western settlement, fire was suppressed directly and indirectly by Euro-American land management practices. Currently, reintroduction of fire into sagebrush steppe systems may be desirable, but long-term fire effects are not well-known. In this 15-year study we used a generalized linear mixed modeling approach to analyze the response of native and invasive grass species to fire in an Artemisia tridentata subsp. wyomingensis (Wyoming big sagebrush) community in north-central Oregon, United States. This study examined responses of Bromus tectorum (cheatgrass), Pseudoroegneria spicata (bluebunch wheatgrass), and Poa secunda (Sandberg bluegrass) along gradients of community type and topography through time post fire. Community types were identified as either A. tridentata subsp. wyomingensis dominant (brush plots) or Juniperus occidentalis (western juniper) dominant (woodland plots). Cover of B. tectorum was greatest in brush plots. B. tectorum cover increased significantly 5 yr post burn and stabilized. At 5 yr, postburn cover of B. tectorum was 135% in brush and 301% in woodland plots of preburn cover. P. spicata was more abundant in woodland plots than in brush plots. In woodland plots, P. spicata cover decreased by 49% 1 yr post burn but returned to preburn cover by 5 yr post burn. On northern exposures recovery of P. spicata cover occurred between 1 and 2 yr post burn, whereas on southern exposures recovery occurred between 2 and 5 yr post burn. The cover of P. secunda did not show a significant response to fire. These results suggest the importance of topography and plant community in determining postfire community response and underscores the importance of place-based studies to guide management and conservation actions.

Exotic grass alters micro-climate and mobility for northern bobwhite chicks

Conservation practices are designed to provide habitat conditions that meet the environmental requirements for species of conservation concern. However, exotic invasive grass species may reduce the efficacy of these practices because they disrupt biological processes. During 7 August–6 September 2001, we investigated 2 possible ecological impacts of bermudagrass (Cynodon dactylon) on northern bobwhite (Colinus virginianus) brood ecology in managed field margins (Laurens County, GA, USA)—reduction in mobility and increased thermal risk. We tested and compared movement rates using imprinted chicks as assays and the thermal environment using in situ temperature probes for bermudagrass and forb habitats. Furthermore, we built upon the existing thermal ecology of northern bobwhite literature and established thermal models to derive time-to-death values from our empirical data. Bermudagrass reduced movement times for chicks 5-days old (0.45 min slower in treatments with bermudagrass), but not for chicks 10-days old. Furthermore, temperatures reached higher daytime temperatures in bermudagrass plots (44.0° C vs. 40.1° C) and crossed the critical hyperthermia threshold more often (32% vs. 11%) than in forb-dominated habitats. Based on simulations, chicks would reach thermal death much earlier in bermudagrass regardless of age. Collectively, our results suggest that bermudagrass reduces habitat quality for bobwhites through reduced movement efficiency and increased thermal stress. Large-scale reductions in bermudagrass are unlikely because of its invasive nature and economic importance to agriculture. However, targeted control or suppression of bermudagrass prior to and following field fallowing is necessary to achieve the objectives of conservation programs for bobwhites and likely other ground-dwelling birds. © 2015 The Wildlife Society.

DEFICIT WATERING REDUCES PLANT GROWTH TO A SMALLER EXTENT WITH ARBUSCULAR MYCORRHIZAL ASSOCIATION THAN WITHOUT IT FOR NON-INVASIVE GRASS SPECIES BUT NOT FOR INVASIVE GRASS SPECIES

Symbiotic associations with the soil microbiota, particularly with arbuscular mycorrhizal fungi (AMF), might ameliorate the effects of environmental stress on plants, and this capacity may be different for resident and alien species. In a growth room pot experiment we tested if imposed water deficit leads to greater growth reduction in the absence of AMF than in the presence of AMF for two non-invasive resident (Danthonia alpina, Chrysopogon gryllus) and two invasive (Calamagrostis epigejos, Cynodon dactylon) grass species from semiarid temperate grasslands in Hungary. Both deficit watering and soil sterilization decreased biomass accumulation, but the non-invasive Danthonia and Chrysopogon performed better when grown in intact soil containing AMF than in sterilized soil. In contrast, the invasive Calamagrostis and Cynodon displayed mostly no difference in growth and biomass accumulation between intact and sterilized soil when subjected to water deficit. When plants were grown well-watered but deprived of AMF symbionts, both Danthonia and Chrysopogon achieved poorer growth than in AMF containing soil, while neither Calamagrostis nor Cynodon displayed any reduction. These results indicate that the influence of deficit watering was ameliorated by the presence of AMF in the soil for the resident non-invasive species, while not for the invasive species.

Interactions between abiotic constraint, propagule pressure, and biotic resistance regulate plant invasion.

With multiple species introductions and rapid global changes, there is a need for comprehensive invasion models that can predict community responses. Evidence suggests that abiotic constraint, propagule pressure, and biotic resistance of resident species each determine plant invasion success, yet their interactions are rarely tested. To understand these interactions, we conducted community assembly experiments simulating situations in which seeds of the invasive grass species Phragmites australis (Poaceae) land on bare soil along with seeds of resident wetland plant species. We used structural equation models to measure both direct abiotic constraint (here moist vs. flooded conditions) on invasion success and indirect constraint on the abundance and, therefore, biotic resistance of resident plant species. We also evaluated how propagule supply of P. australis interacts with the biotic resistance of resident species during invasion. We observed that flooding always directly reduced invasion success but had a synergistic or antagonistic effect on biotic resistance depending on the resident species involved. Biotic resistance of the most diverse resident species mixture remained strong even when abiotic conditions changed. Biotic resistance was also extremely effective under low propagule pressure of the invader. Moreover, the presence of a dense resident plant cover appeared to lower the threshold at which invasion success became stable even when propagule supply increased. Our study not only provides an analytical framework to quantify the effect of multiple interactions relevant to community assembly and species invasion, but it also proposes guidelines for innovative invasion management strategies based on a sound understanding of ecological processes.

Experimental evidence that invasive grasses use allelopathic biochemicals as a potential mechanism for invasion: chemical warfare in nature

Background and aims Bothriochloa spp. are non-native warm-season grasses invading native grasslands of the southern and central Great Plains, altering ecological services these grasslands supply. Our study investigated potential allelopathic effects of the invasive grass species B. ischaemum on native grass germination, growth, and survival.

Optimal approaches for balancing invasive species eradication and endangered species management.

Resolving conflicting ecosystem management goals-such as maintaining fisheries while conserving marine species or harvesting timber while preserving habitat-is a widely recognized challenge. Even more challenging may be conflicts between two conservation goals that are typically considered complementary. Here, we model a case where eradication of an invasive plant, hybrid Spartina, threatens the recovery of an endangered bird that uses Spartina for nesting. Achieving both goals requires restoration of native Spartina. We show that the optimal management entails less intensive treatment over longer time scales to fit with the time scale of natural processes. In contrast, both eradication and restoration, when considered separately, would optimally proceed as fast as possible. Thus, managers should simultaneously consider multiple, potentially conflicting goals, which may require flexibility in the timing of expenditures.

Conservation vs. eradication

Conservation Ecology![Figure][1] PHOTO: © LIFE ON WHITE/ALAMY ![Figure][1] Endangered California clapper rail. PHOTO: ROBERT CLARK What's an ecologist to do when an endangered bird lives in an invasive grass? Ecosystems are complicated networks, with one species relying on another, and managing one species in isolation may damage other members of a community. Lampert et al. (see the Perspective by Buckley and Han) looked at the conflict between eradicating a damaging invasive grass species and protecting an endangered bird species that uses the grass as its home. The most effective management and restoration approach focused not on eradicating the invasive grass as quickly as possible but on making changes slowly enough that the birds could adapt. This approach may prove useful in other situations in which active restoration conflicts with other conservation goals. Science , this issue p. [1028][2]; see also p. [975][3] [1]: pending:yes [2]: /lookup/doi/10.1126/science.1250763 [3]: /lookup/doi/10.1126/science.1254662

Invasion Success in Cogongrass (Imperata cylindrica): A Population Genetic Approach Exploring Genetic Diversity and Historical Introductions

AbstractPropagule pressure significantly contributes to and limits the potential success of a biological invasion, especially during transport, introduction, and establishment. Events such as multiple introductions of foreign parent material and gene flow among them can increase genetic diversity in founding populations, often leading to greater invasion success. We applied the tools and theory of population genetics to better understand the dynamics of successful biological invasion. The focal species, cogongrass, is a perennial invasive grass species significantly affecting the Gulf Coast and southeastern region of the United States. The literature indicates separate, allopatric introductions of material from East Asia (Philippines and Japan) into the U.S. states of Mississippi and Alabama. Molecular analysis of samples from those two states utilized amplified fragment length polymorphism (AFLP) markers on 388 individuals from 21 localities. We hypothesized that previously isolated lineages of cogongrass are present and crossing in the Southeast. We observed genetic variation within localities (0.013 ≤ heterozygosity (He) ≤ 0.051, mean = 0.028 ± 0.001) with significant and substantial population structure (FST= 0.534, P < 0.001). Population structure analyses detected two genetically defined and statistically supported populations, which appear to have experienced some admixture. The geographic distribution of those populations was consistent with the two-introduction scenario reported previously. These results are also consistent with contact in the invasive range of previously isolated lineages from the native range.

The effects of precipitation and soil type on three invasive annual grasses in the western United States

Multiple species of annual grasses are invading sagebrush-steppe communities throughout the western United States. Most research has focused on dominant species such as Bromus tectorum (cheatgrass), yet other, less studied annual grasses such as Taeniatherum caput-medusae (medusahead) and Ventenata dubia (ventenata) are spreading rapidly. Future precipitation regimes are expected to have less frequent but more intense rain events, which may affect soil moisture availability and favor these ‘newer’ invasives over cheatgrass. We conducted a full factorial, growth chamber study examining the effects of two watering regimes (small/frequent, large/infrequent rain pulses) across nine soil types on the growth of cheatgrass, medusahead and ventenata. We tested a hypothesis that medusahead or ventenata would have greater growth than cheatgrass with larger/infrequent rain events. The two watering regimes had relatively strong effects on soil water content, but generally did not impact plant growth. In contrast, variation in soil properties such as clay content, pH and soil N correlated with a two- to four-fold change in plant growth. The three invasive grass species generally respond similarly to changes in precipitation regimes and to edaphic factors. Nevertheless, medusahead had 30–40% overall greater root growth compared to the other species and a 15% increase in root growth in response to the large/infrequent watering treatment. Our findings reveal that 1) greater biomass allocation to roots and 2) greater responsiveness of root growth to differing precipitation regimes of medusahead may favor its ecological success over other invasive annuals under future climate scenarios.

Tall fescue is a potential spillover reservoir host for Alternaria species

The spread of invasive species is complicated and multifaceted. Enemy spillover (i.e. the transfer of a natural enemy from a reservoir host to a novel host) is one mechanism that facilitates the spread of non-native species. The reservoir host is a species that harbors high abundance of the enemy with little cost to fitness. We asked whether Schedonorus arundinaceus (tall fescue), a highly invasive grass species in North America, is a potential reservoir host for the ubiquitous genus of fungi, Alternaria. We also asked whether spillover of Alternaria is possible among grasses that commonly occur with S. arundinaceus in grassland ecosystems. We performed a greenhouse cross inoculation of three isolates of Alternaria and six grass species (three native, three invasive, including S. arundinaceus). We determined that spillover is possible because the fungal isolates infected and caused disease symptoms on all six grasses and decreased biomass in two of the grass species. We also determined that the invasive grass species appear to be more competent hosts than the native species and that S. arundinaceus could be a likely reservoir host for Alternaria spp. because it can harbor the pathogen with no apparent fitness cost.

GENERAL EQUILIBRIUM ECOSYSTEM MODELING WITH ALTERNATIVE PREFERENCE SPECIFICATIONS

AbstractThis paper reconciles two sets of literature with regard to the interactive ecological and economic impacts of invasive grass species and cattle stocking. We model cattle as optimal foragers, satiation foragers, and proportional foragers in order to understand the impact that each assumption imposes on predicted economic and ecological outcomes. Through this model sensitivity (as opposed to parameter sensitivity) analysis, we are able to identify three main drivers of plant invasions: exogenous forces such as climate change or nitrogen deposition, poor land management decisions, and a misalignment of incentives between cattle and ranchers even when ranchers behave optimally.

Status of exotic grasses and grass-like vegetation and potential impacts on wildlife in New England

The Northeastern section of the United States, known as New England, has seen vast changes in land cover and human population over the past 3 centuries. Much of the region is forested; grasslands and other open-land cover types are less common, but provide habitat for many species that are currently declining in abundance and distribution. New England also consists of some of the most densely populated and developed states in the country. The origin, distribution, and spread of exotic species are highly correlated with human development. As such, exotics are common throughout much of New England, including several species of graminoids (grasses and grass-like plants such as sedges and rushes). Several of the more invasive grass species can form expansive dense mats that exclude native plants, alter ecosystem structure and functions, and are perceived to provide little-to-no value as wildlife food or cover. Although little research has been conducted on direct impacts of exotic graminoids on wildlife populations in New England, several studies on the common reed (Phragmites australis) in salt marshes have shown this species to have variable effects as cover for birds and other wildlife, depending on the distribution of the plant (e.g., patches and borders of reeds are used more by wildlife than expansive densely growing stands). Direct impacts of other grasses on wildlife populations are largely unknown. However, many of the invasive graminoid species that are present in New England have the capability of outcompeting native plants and thereby potentially affecting associated fauna. Preservation, protection, and restoration of grassland and open-land cover types are complex but necessary challenges in the region to maintain biological and genetic diversity of grassland, wetland, and other open-land obligate species. © 2013 The Wildlife Society.

The behavior of multiple independent managers and ecological traits interact to determine prevalence of weeds

Management of damaging invasive plants is often undertaken by multiple decision makers, each managing only a small part of the invader's population. As weeds can move between properties and re-infest eradicated sites from unmanaged sources, the dynamics of multiple decision makers plays a significant role in weed prevalence and invasion risk at the landscape scale. We used a spatially explicit agent-based simulation to determine how individual agent behavior, in concert with weed population ecology, determined weed prevalence. We compared two invasive grass species that differ in ecology, control methods, and costs: Nassella trichotoma (serrated tussock) and Eragrostis curvula (African love grass). The way decision makers reacted to the benefit of management had a large effect on the extent of a weed. If benefits of weed control outweighed the costs, and either net benefit was very large or all agents were very sensitive to net benefits, then agents tended to act synchronously, reducing the pool of infested agents available to spread the weed. As N. trichotoma was more damaging than E. curvula and had more effective control methods, agents chose to manage it more often, which resulted in lower prevalence of N. trichotoma. A relatively low number of agents who were intrinsically less motivated to control weeds led to increased prevalence of both species. This was particularly apparent when long-distance dispersal meant each infested agent increased the invasion risk for a large portion of the landscape. In this case, a small proportion of land mangers reluctant to control, regardless of costs and benefits, could lead to the whole landscape being infested, even when local control stopped new infestations. Social pressure was important, but only if it was independent of weed prevalence, suggesting that early access to information, and incentives to act on that information, may be crucial in stopping a weed from infesting large areas. The response of our model to both behavioral and ecological parameters was highly nonlinear. This implies that the outcomes of weed management programs that deal with multiple land mangers could be highly variable in both space and through time.

An Invasive Grass Increases Live Fuel Proportion and Reduces Fire Spread in a Simulated Grassland

Fire is a globally important ecosystem process, and invasive grass species generally increase fire spread by increasing the fuel load and continuity of native grassland fuelbeds. We suggest that invasive grasses that are photosynthetically active, while the native plant community is dormant reduce fire spread by introducing high-moisture, live vegetation gaps in the fuelbed. We describe the invasion pattern of a high-moisture, cool-season grass, tall fescue (Schedonorus phoenix (Scop.) Holub), in tallgrass prairie, and use spatially explicit fire behavior models to simulate fire spread under several combinations of fuel load, invasion, and fire weather scenarios. Reduced fuel load and increased extent of tall fescue invasion reduced fire spread, but high wind speed and low relative humidity can partially mitigate these effects. We attribute reduced fire spread to asynchrony in the growing seasons of the exotic, cool-season grass, tall fescue, and the native, warm-season tallgrass prairie community in this model system. Reduced fire spread under low fuel load scenarios indicate that fuel load is an important factor in fire spread, especially in invaded fuel beds. These results present a novel connection between fire behavior and asynchronous phenology between invasive grasses and native plant communities in pyrogenic ecosystems.