Plant Population Dynamics Research Articles

Nutrient availability and senescence spatially structure the dynamics of a foundation species

Disentangling the roles of the external environment and internal biotic drivers of plant population dynamics is challenging due to the absence of relevant physiological and abundance information over appropriate space and time scales. Remote observations of giant kelp biomass and photosynthetic pigment concentrations are used to show that spatiotemporal patterns of physiological condition, and thus growth and production, are regulated by different processes depending on the scale of observation. Nutrient supply was linked to regional scale (>1 km) physiological condition dynamics, and kelp forest stands were more persistent where nutrient levels were consistently high. However, on local scales (<1 km), internal senescence processes related to canopy age demographics determined patterns of biomass loss across individual kelp forests despite uniform nutrient conditions. Repeat measurements of physiology over continuous spatial fields can provide insights into complex dynamics that are unexplained by the environmental drivers thought to regulate abundance. Emerging remote sensing technologies that provide simultaneous estimates of abundance and physiology can quantify the roles of environmental change and demographics governing plant population dynamics for a wide range of aquatic and terrestrial ecosystems.

Weather‐driven demography and population dynamics of an endemic perennial plant during a 34‐year period

Abstract Increased anthropogenic influence on the environment has accentuated the need to assess how climate and other environmental factors drive vital rates and population dynamics of different types of organisms. However, to allow distinction between the effects of multiple correlated variables, and to capture the effects of rare and extreme climatic conditions, studies extending over decades are often necessary. In this study, we used an individual‐based dataset collected in three populations of Pulsatilla vulgaris subsp. gotlandica during 34 years, to explore the effects of variation in precipitation and temperature on vital rates and population dynamics. Most of the observed conspicuous variation in flowering among years was associated with differences in precipitation and temperature in the previous summer and autumn with a higher incidence of flowering following summers with high precipitation and low temperatures. In contrast, climatic variables had no significant effects on individual growth or survival. Although the weather‐driven variation in flowering had only moderate absolute effects on the population growth rate, simulated persistent changes in average precipitation and temperature resulted in considerable reductions in population sizes compared with current conditions. Analyses carried out with subsets of data consisting of 5 and 10 years yielded results that strongly deviated from those based on the full dataset. Synthesis. The results of this study illustrate the importance of long‐term demographic monitoring to identify key climatic variables affecting vital rates and driving population dynamics in long‐lived organisms.

Climate warming and extended droughts drive establishment and growth dynamics in temperate grassland plants

Current climate warming and extended droughts have major impacts on plant performance, with consequences for biodiversity and ecosystem functioning. However, unlike in trees, little is known about species-specific responses in grassland plants and the role of their different life histories in mitigating climate change impacts. We studied the climate-related plant establishment and growth dynamics over the last thirty years in four Central European grassland species with contrasting rooting depth, seed mass and xylem anatomy, and hence ability to cope with drought-induced restriction on establishment and growth. To assess the annual and seasonal dependency on fluctuating temperature and precipitation, we reconstructed establishment and growth chronologies from 174 individuals spanning 1–29 years, and more than 2,500 annual growth increments. We identified contrasting climatic controls of establishment and growth among focal species, which were likely related to their different traits. The establishment of deep-rooted, heavy-seeded species profited from increased winter and early spring precipitation, while the establishment of shallow-rooted, light-seeded species was weakly influenced by climate fluctuations. However, their growth was more adversely affected by high summer temperatures and drought than the growth of deep-rooted species. Our results show that the change towards a warmer and drier climate over the past thirty years profoundly reduced the growth and establishment of studied grassland plants. Most individuals established in the wet period of the 2000s, but the establishment reduced considerably during the dry and warm period of the 2010s. Our results provide novel insights into species-specific climate dependency of plant establishment, growth and population dynamics, suggesting the high vulnerability of Central European grasslands to climate warming.

The mutualism-antagonism continuum in Neotropical palm-frugivore interactions: from interaction outcomes to ecosystem dynamics.

ABSTRACTFrugivory, that is feeding on fruits, pulp or seeds by animals, is usually considered a mutualism when interactions involve seed dispersal, and an antagonism when it results in the predation and destruction of seeds. Nevertheless, most frugivory interactions involve both benefits and disadvantages for plants, and the net interaction outcomes thus tend to vary along a continuum from mutualism to antagonism. Quantifying outcome variation is challenging and the ecological contribution of frugivorous animals to plant demography thus remains little explored. This is particularly true for interactions in which animals do not ingest entire fruits, that is in seed‐eating and pulp‐eating. Here, we provide a comprehensive review of Neotropical palm–frugivore interactions, with a focus on how frugivore consumption behaviour (i.e. digestive processing, fruit‐handling ability and caching behaviour) and feeding types (fruit‐eating, pulp‐eating and seed‐eating) influence interaction outcomes at different demographic stages of palms. We compiled a total of 1043 species‐level palm–frugivore interaction records that explicitly captured information on which parts of palm fruits are eaten by animals. These records showed consumption of fruits of 106 Neotropical palm species by 273 vertebrate species, especially birds (50%) and mammals (45%), but also fish (3%) and reptiles (2%). Fruit‐eating involved all four taxonomic vertebrate classes whereas seed‐eating and pulp‐eating were only recorded among birds and mammals. Most fruit‐eating interactions (77%) resulted in positive interaction outcomes for plants (e.g. gut‐passed seeds are viable or seeds are successfully dispersed), regardless of the digestive processing type of vertebrate consumers (seed defecation versus regurgitation). The majority of pulp‐eating interactions (91%) also resulted in positive interaction outcomes, for instance via pulp removal that promoted seed germination or via dispersal of intact palm seeds by external transport, especially if animals have a good fruit‐handling ability (e.g. primates, and some parrots). By contrast, seed‐eating interactions mostly resulted in dual outcomes (60%), where interactions had both negative effects on seed survival and positive outcomes through seed caching and external (non‐digestive) seed dispersal. A detailed synthesis of available field studies with qualitative and quantitative information provided evidence that 12 families and 27 species of mammals and birds are predominantly on the mutualistic side of the continuum whereas five mammalian families, six mammal and one reptile species are on the antagonistic side. The synthesis also revealed that most species can act as partial mutualists, even if they are typically considered antagonists. Our review demonstrates how different consumption behaviours and feeding types of vertebrate fruit consumers can influence seed dispersal and regeneration of palms, and thus ultimately affect the structure and functioning of tropical ecosystems. Variation in feeding types of animal consumers will influence ecosystem dynamics via effects on plant population dynamics and differences in long‐distance seed dispersal, and may subsequently affect ecosystem functions such as carbon storage. The quantification of intra‐ and inter‐specific variation in outcomes of plant–frugivore interactions – and their positive and negative effects on the seed‐to‐seedling transition of animal‐dispersed plants – should be a key research focus to understand better the mutualism–antagonism continuum and its importance for ecosystem dynamics.

Seed dispersal by wind decreases when plants are water-stressed, potentially counteracting species coexistence and niche evolution.

Hydrology is a major environmental factor determining plant fitness, and hydrological niche segregation (HNS) has been widely used to explain species coexistence. Nevertheless, the distribution of plant species along hydrological gradients does not only depend on their hydrological niches but also depend on their seed dispersal, with dispersal either weakening or reinforcing the effects of HNS on coexistence. However, it is poorly understood how seed dispersal responds to hydrological conditions. To close this gap, we conducted a common‐garden experiment exposing five wind‐dispersed plant species (Bellis perennis, Chenopodium album, Crepis sancta, Hypochaeris glabra, and Hypochaeris radicata) to different hydrological conditions. We quantified the effects of hydrological conditions on seed production and dispersal traits, and simulated seed dispersal distances with a mechanistic dispersal model. We found species‐specific responses of seed production, seed dispersal traits, and predicted dispersal distances to hydrological conditions. Despite these species‐specific responses, there was a general positive relationship between seed production and dispersal distance: Plants growing in favorable hydrological conditions not only produce more seeds but also disperse them over longer distances. This arises mostly because plants growing in favorable environments grow taller and thus disperse their seeds over longer distances. We postulate that the positive relationship between seed production and dispersal may reduce the concentration of each species to the environments favorable for it, thus counteracting species coexistence. Moreover, the resulting asymmetrical gene flow from favorable to stressful habitats may slow down the microevolution of hydrological niches, causing evolutionary niche conservatism. Accounting for context‐dependent seed dispersal should thus improve ecological and evolutionary models for the spatial dynamics of plant populations and communities.

Disease influences host population growth rates in a natural wild plant–pathogen association over a 30‐year period

Abstract The epidemiological and demographic dynamics of plant–pathogen interactions in natural environments are strongly affected by spatial and temporal influences. Here we assess the interaction between Filipendula ulmaria and its rust pathogen Triphragmium ulmariae by analysing a 30‐year long dataset that has followed pathogen and plant population dynamics in a metapopulation of ~230 host patches growing on islands of the Skeppsvik archipelago in northern Sweden. Over this period, the host metapopulation initially expanded in both number and size of individual patches before plateauing. In contrast, the pathogen metapopulation showed greater change. Disease incidence showed a convex pattern rising for the first decade before showing a marked decline in the last decade. At the same time, the prevalence of disease in infected populations showed a constant 30‐year long decline. At the individual host population level, each population was annually classified into one of four inter‐year states: healthy, recolonization, extinction and diseased. Host populations that were healthy from 1 year to the next were significantly smaller than all other host population categories, while host populations in which disease was constantly present were significantly larger. Host populations in which the pathogen underwent either an extinction or a recolonization event were of similar size and represented a measure of the host threshold size for long‐term pathogen survival. Host population growth rates declined as disease levels increased. The growth rate of host populations in which disease was continuously present was 75% lower than in populations that were free disease. The sensitivity of the association to climate change as demonstrated through a decline in disease incidence and prevalence and an increase in drought damage to plant populations as temperatures rise has only become apparent through analysis of an extensive long‐term dataset. Synthesis. To date wild plant–pathogen studies have focused on the epidemiology of the pathogen and its effect on individual plant fitness. Here we have established a link to the impact of the pathogen on the long‐term dynamics of host populations. This has the potential to trigger a cascade of changes in the species composition and diversity of communities.

Quantifying seed and establishment limitation to seedling recruitment of arable weeds: an example of barnyardgrass (Echinochloa crus-galli)

AbstractThe establishment of plants in an ecosystem is limited by the availability of seeds and the availability of suitable sites for establishment. Describing plant population dynamics through the relative strength of seed and establishment limitation is an important concept in the study of natural ecosystems. To date, it is unclear whether this concept can be applied to describe populations of annual weeds in agricultural fields. Using a recruitment function, we show that limitation parameters prove valuable in describing seedling recruitment in weed populations. We conducted a seed addition experiment in three cornfields (Zea maysL.) and recorded seedling recruitment in populations of the economically important weed barnyardgrass [Echinochloa crus-galli(L.) P. Beauv.]. Seed predation, competition with other weeds, and seed burial were prevented. We estimated the strength of seed and establishment limitation in the population with two parameters:n, which is the number of microsites, andb, which is the suitability of those sites to support a seedling. We further estimated the relative proportions of density-dependent and density-independent establishment limitation in the seedling population. Recruitment rates ofE. crus-galliranged from 31% to 36% across all evaluated seed densities and fields, which is high compared with results from other seed addition studies. Two of the three monitored populations were predominantly establishment limited at the highest evaluated seed density of 2,400 added seeds m−2. Further knowledge about the relative strength of limitations in other weed populations will provide important information on how effective different weed management strategies can be.

Acorn Crop, Seed Size and Chemical Defenses Determine the Performance of Specialized Insect Predators and Reproductive Output in a Mediterranean Oak.

Simple SummarySeed predation is an antagonistic interaction that can limit plant population dynamics. We investigated the interaction between Quercus faginea and two specialized pre-dispersal insect seed predators (weevils and moths) during two years of contrasting crop size to determine the consequences of oak reproductive investment on seed production and insect performance. Crop and acorn size were lower during the second year, although seed predation rates by insects were similar during both crop years. Oaks producing more acorns reduced seed predation by insects during the large crop year and thus improved their reproductive success, and those producing bigger acorns experienced higher levels of seed predation, and more insect larvae developed inside the available acorns during the low crop year. Inter- and intra-specific insect competition increased during the low crop year and were affected by tannin content in acorns. Despite substantial between-year variations in crop and acorn size, insect performance was similar due to larvae being able to finish their development by depleting acorn reserves when resources were low. Crop size, acorn size and chemical composition seem important traits for reducing seed predation by specialized insects and improve reproductive success in this Mediterranean oak species.Seed predation is an antagonistic interaction that negatively affects the performance of individual plants and can limit plant population dynamics. In animal-dispersed plants, crop size is an important determinant of plant reproductive success through its effect on seed dispersers and predators. Seed traits, such as size or chemical composition, can also increase the tolerance to seed predators or reduce their performance. We investigated the interaction between Quercus faginea and two specialized pre-dispersal insect seed predators (weevils and moths) during two years of contrasting crop size to determine the consequences of oak reproductive investment on seed production and insect performance. Crop size was 44% lower and acorns were 32% smaller in the second year, although acorn predation by insects was proportionally similar between both years at the population level. Individual trees producing larger crops showed a lower incidence of insect predators during the year of abundant acorn production, whereas trees producing bigger acorns experienced higher seed predation rates by insects, and acorns held more insect larvae in the low crop year. Competition between insects increased when acorn production was low, and higher tannin content in acorns further constrained the number of weevil larvae developing together in the same acorn. However, the abundance and size of insect larvae produced per tree were similar between the two crop years, and this was due to larvae often depleting acorn reserves when resources were low. Oak reproductive output increased nearly two-fold during the large crop year. Crop size variation, acorn production in a given year and acorn size and chemical composition seem to be important traits for reducing damage by insect predators in Quercus faginea and improve oak reproductive success.

An assessment of the role of soil organic matter in pasture resilience

This paper assesses the role of soil organic matter (SOM) in pasture resilience and longevity. New Zealand pasture soils have high levels of SOM, which contribute to soil structural stability and nutrient cycling, functions that support resilient pasture. It is concluded that pasture resilience requires (a) a pasture-soil system that returns regular amounts of fresh, ‘labile’ carbon (C) since this younger SOM fraction plays a significant role in these processes, and (b) a thriving soil biota that can rapidly turn over this labile C. Pasture itself also plays a critical role as the major pathway for C transfer into the soil rhizosphere, with differences between species in amounts and composition of C returns. Resident (older) SOM should not be ignored and plays a role in sustaining soil structure, but the younger SOM is the fraction that turns over more often and plays a key role in nutrient supply.Soil organic matter is not a single solution to increasing pasture resilience since soil type and summer rainfall have been previously identified as key factors also. However, other identified factors such as plant nitrogen status, plant population dynamics and grazing management either influence or are influenced by the turnover of SOM, suggesting its role in pasture resilience should not be underestimated.

What are the demographic consequences of a seed bank stage for columnar cacti?

AbstractThe dynamics of plant populations are often limited by the early stages in their life cycles. However, information regarding seed bank dynamics and how these may influence the whole life cycle of plant species is remarkably scarce or not considered explicitly. This lack of knowledge is due mainly to the challenges in quantifying seed vital rates. Studies of arid land plant species have historically been focused on the drivers of sporadic recruitment. However, little attention has been given to the demographic consequences of early developmental stages, and how seed banks affect their dynamics. Here, we evaluate the effects of seed bank survival and seedling recruitment vital rates on the population dynamics and viability of 12 columnar cacti species. Recent evidence suggests that cacti seeds may remain viable for the short‐term. We assess how changes in the vital rates of these processes and the inclusion of a seed bank affect population growth rate (λ). We found that a seed bank in the examined matrix population models significantly increased λ as well as the vital rate elasticities of λ to growth and fecundity, whereas that of overall survival decreased. Our numerical simulations showed that seed survival had a more considerable effect on λ than seedling recruitment and establishment. We suggest that the seed bank may explain the structure and population dynamics. Thus, we reconsider that this early stage in demographic models will generate more informed decisions on the conservation and management of columnar cacti.

Climate change and grassland management interactively influence the population dynamics of Bromus erectus (Poaceae)

Climate and land management are important environmental drivers that affect the structure of terrestrial plant communities worldwide. Demographic studies allow a mechanistic understanding of the pathways in which environmental factors change population size. Climate and land management might interactively influence vital rates and growth rates of populations, however, demographic studies have not heretofore considered both factors in combination. We used the Global Change Experimental Facility as a platform to study the effect of climate (ambient climate conditions vs. future climate conditions) and land management (sheep grazing vs. mowing) on the demography of the common grass, Bromus erectus growing in semi-natural grassland communities. Using an integral projection model, we found positive population growth rates for B. erectus under all treatment combinations, and an interactive effect of climate and land management. Under ambient climate conditions, population growth of B. erectus was higher in mowed than grazed grassland plots, while population growth rates were similar across both management types under future climatic conditions. This interaction was primarily due to between-treatment changes in seedling recruitment, a vital rate to which the population growth rate is particularly sensitive. The interaction found in this study highlights the importance of considering multiple environmental drivers in demographic studies, to better predict future plant population dynamics and ultimately changes in community structure.

Modeling scale up of anthropogenic impacts from individual pollinator behavior to pollination systems.

Understanding how anthropogenic disturbances affect plant–pollinator systems has important implications for the conservation of biodiversity and ecosystem functioning. Previous laboratory studies show that pesticides and pathogens, which have been implicated in the rapid global decline of pollinators over recent years, can impair behavioral processes needed for pollinators to adaptively exploit floral resources and effectively transfer pollen among plants. However, the potential for these sublethal stressor effects on pollinator–plant interactions at the individual level to scale up into changes to the dynamics of wild plant and pollinator populations at the system level remains unclear. We developed an empirically parameterized agent‐based model of a bumblebee pollination system called SimBee to test for effects of stressor‐induced decreases in the memory capacity and information processing speed of individual foragers on bee abundance (scenario 1), plant diversity (scenario 2), and bee–plant system stability (scenario 3) over 20 virtual seasons. Modeling of a simple pollination network of a bumblebee and four co‐flowering bee‐pollinated plant species indicated that bee decline and plant species extinction events could occur when only 25% of the forager population showed cognitive impairment. Higher percentages of impairment caused 50% bee loss in just five virtual seasons and system‐wide extinction events in less than 20 virtual seasons under some conditions. Plant species extinctions occurred regardless of bee population size, indicating that stressor‐induced changes to pollinator behavior alone could drive species loss from plant communities. These findings indicate that sublethal stressor effects on pollinator behavioral mechanisms, although seemingly insignificant at the level of individuals, have the cumulative potential in principle to degrade plant–pollinator species interactions at the system level. Our work highlights the importance of an agent‐based modeling approach for the identification and mitigation of anthropogenic impacts on plant–pollinator systems.

Soil biota and soil substrates influence responses of the rhizomatous clonal grass Leymus chinensis to nutrient heterogeneity

The positive effects of spatial heterogeneity in soil nutrients on plant performance have been well documented, but whether such effects depend on the presence of soil biota or the substrate type in which the heterogeneity is manipulated remains largely unknown. In a greenhouse experiment, we grew the rhizomatous clonal grass Leymus chinensis in three different substrates (i.e., field soil, potting soil, and mixtures of ceramsite and quartz) that were subjected to two different soil nutrient treatments (i.e., a homogeneous treatment and a heterogeneous treatment consisting of low- and high-nutrient soil patches) and inoculated with either live or sterilized soil biota. In the presence of the live soil biota, L. chinensis produced more biomass in the homogeneous than in the heterogeneous treatment, independent of the substrate type. With the sterilized soil biota, however, L. chinensis produced more biomass in the heterogeneous than in the homogeneous treatment. In the heterogeneous treatment consisting of the field soil and the potting soil, L. chinensis produced more biomass in the high-nutrient patches than in the low-nutrient patches. In contrast, it produced more biomass in the low-nutrient patches than in the high-nutrient patches in the heterogeneous treatment consisting of the field soil and the mixture of quartz and ceramsite. Both soil biota and soil substrates can influence the responses of clonal plants to soil nutrient heterogeneity. Our results highlight the vital importance of including soil biota and soil physical properties in studies designed to examine the effects of soil nutrient heterogeneity on plant performance, population dynamics, species coexistence and ecosystem functioning.

Plant community persistence strategy is elevation‐specific

AbstractAimsPersistence plays a key role in both plant population and community dynamics as it allows withstanding temporarily habitat conditions unsuitable for growth and reproduction. Plants can exploit three different strategies to persist in situ (building soil seed banks, increasing adult longevity and/or clonal reproduction), the dominance of which in a community might vary along environmental gradients. Yet, their relative role in plant persistence has never been investigated.LocationThe Bavarian Alps, Germany.MethodsWe collected data on seed soil persistence, adult longevity and clonality for 290 species occurring in 18 grasslands located along an elevational gradient of 1,000 metres and examined their contribution to persistence in a community. Linear models were used to estimate the relationship between elevation and these persistence strategies.ResultsWe found that dominance of a certain persistence strategy varied depending on environmental variability. Specifically, persistence in lowlands was mainly achieved by persistent and dense soil seed banks along with extended clonal growth (larger spread distances and higher number of offspring). Contrastingly, the main persistence strategy in the alpine communities was increased adult longevity.ConclusionsThe changes in relative contribution of each strategy to community persistence along the elevational gradient are interrelated suggesting a trade‐off among them. We conclude that this trade‐off plays an important role in species co‐existence and community assembly, and might be useful to understand vegetation dynamics under ongoing climate change and improve restoration efforts of upland ecosystems.

Demographic analysis of an Israeli Carpobrotus population.

Carpobrotus species are harmful invaders to coastal areas throughout the world, particularly in Mediterranean habitats. Demographic models are ideally suited to identify and understand population processes and stages in the life cycle of the species that could be most effectively targeted with management. However, parameterizing these models has been limited by the difficulty in accessing the cliff-side locations where its populations are typically found, as well as accurately measuring the growth and spread of individuals, which form large, dense mats. This study uses small unmanned aerial vehicles (drones) to collect demographic data and parameterize an Integral Projection Model of an Israeli Carpobrotus population. We validated our data set with ground targets of known size. Through the analysis of asymptotic growth rates and population sensitivities and elasticities, we demonstrate that the population at the study site is demographically stable, and that reducing the survival and growth of the largest individuals would have the greatest effect on reducing overall population growth rate. Our results provide a first evaluation of the demography of Carpobrotus, a species of conservation and economic concern, and provide the first structured population model of a representative of the Aizoaceae family, thus contributing to our global knowledge on plant population dynamics. In addition, we demonstrate the advantages of using drones for collecting demographic data in understudied habitats such as coastal ecosystems.

Impacts of plant invasions in native plant-pollinator networks.

The disruption of mutualisms by invasive species has consequences for biodiversity loss and ecosystem function. Although invasive plant effects on the pollination of individual native species has been the subject of much study, their impacts on entire plant-pollinator communities are less understood. Community-level studies on plant invasion have mainly focused on two fronts: understanding the mechanisms that mediate their integration; and their effects on plant-pollinator network structure. Here we briefly review current knowledge and propose a more unified framework for evaluating invasive species integration and their effects on plant-pollinator communities. We further outline gaps in our understanding and propose ways to advance knowledge in this field. Specifically, modeling approaches have so far yielded important predictions regarding the outcome and drivers of invasive species effects on plant communities. However, experimental studies that test these predictions in the field are lacking. We further emphasize the need to understand the link between invasive plant effects on pollination network structure and their consequences for native plant population dynamics (population growth). Integrating demographic studies with those on pollination networks is thus key in order to achieve a more predictive understanding of pollinator-mediated effects of invasive species on the persistence of native plant biodiversity.

Developing hierarchical density‐structured models to study the national‐scale dynamics of an arable weed

AbstractPopulation dynamics can be highly variable in the face of environmental heterogeneity, and understanding this variation is central in the study of ecology. Robust management decisions require that we understand how populations respond to management at a range of scales, and under a broad suite of conditions. Population models are potentially valuable tools in addressing this challenge. However, without adequate data, models can fail to produce useful results. Populations of arable weeds are particularly problematic in this respect, as they are widespread and their dynamics are extremely variable. Owing to the inherent cost of collecting data, most studies of plant population dynamics are derived from localized experiments under a small range of environmental conditions, limiting the extent to which variance in population dynamics can be measured. Density‐structured models provide a route to rapid, large‐scale analysis of population dynamics, and can expand the scale of ecological models that are directly tied to data. Here we extend previous density‐structured models to include environmental heterogeneity, variation in management, and to account for inter‐population variation. We develop, parameterize, and test hierarchical density‐structured models for a common agricultural weed, black‐grass (Alopecurus myosuroides). We model the dynamics of this species in response to crop management, using survey data gathered over 4 yr from 364 fields across a network of 45 UK farms. We show that hierarchical density‐structured models provide a substantial improvement over their nonhierarchical counterparts. Using these models, we demonstrate that several alternative crop rotations are effective in reducing weed densities. Rotations with high wheat prevalence exhibit the most severe infestations, and diverse rotations generally have lower weed densities. However, a key outcome is that in many cases the effect of crop rotation is small compared to the high variability arising from spatiotemporal heterogeneity. This result highlights the need to monitor and model population dynamics across large spatial and temporal scales in order to account for variation in the drivers of plant dynamics. Our framework for data collection and modeling provides a means to achieve this.

Human‐induced reduction in mammalian movements impacts seed dispersal in the tropics

Seed dispersal is a key process affecting the structure, composition and spatial dynamics of plant populations. Numerous plant species in the tropics rely upon animals to disperse their seeds. Humans have altered mammalian movements, which will likely affect seed dispersal distances (SDD). Altered SDD may have a range of consequences for plant communities including reduced seedling recruitment and plant biomass, seed trait homogenization, altered gene flow and a reduced capacity to respond to environmental changes. Therefore, modelling the consequences of altered animal behaviour on ecosystem processes is important for predicting how ecosystems will respond to human impacts. While previous research has focused on the link between animal species extirpation and SDD, it remains unclear how changes in mammalian movement will impact SDD. Here we implemented a mechanistic modelling approach to examine how mammalian movement reductions impact SDD in the tropics. We combined allometric theory with a mechanistic seed dispersal model to estimate SDD via the movement of 37 large frugivorous mammals (&gt; 10 kg) in the tropics under different levels of human footprint, a global proxy of direct and indirect human disturbances. Our results suggest that assemblage‐level SDD reductions are estimated to be up to 80% across the tropics in response to human disturbance. This is particularly the case in areas with high human impact such as agricultural landscapes and suburban areas. The region with the largest reductions in SDD was the Asia‐Pacific with average reductions of 25%, followed by Central–South America (16%) and then Africa (15%). Our study provides insights into how human‐induced changes in movement behaviour of large mammals could translate into altered ecosystem functioning.

Microbial Population Dynamics in Model Sewage Treatment Plants and the Fate and Effect of Gold Nanoparticles.

Adequate functioning of a sewage treatment plant (STP) is essential to protect the downstream aquatic environment (ECHA 2017), and information on the degradability of chemicals and their toxicity to activated sludge microorganisms is required. An environmental realistic higher tier test is a STP simulation test as described in OECD 303A (2001) which for nanoparticles can also be used to study their sorption behavior to activated sludge. However, information is limited on the influence of synthetic sewage on the microbial community of the activated sludge. A modified community can result in modifications of the sludge floccules affecting the sorption behavior. The main objective of our study was to show whether a representative microbial diversity remains under standardized test conditions as described in OECD 303A (2001) using synthetic sewage as influent. Furthermore, we investigated whether just considering the functional properties of a STP (elimination of dissolved organic carbon; nitrification), is sufficient for an assessment of gold nanoparticles (AuNPs) or whether the influence on microbial diversity also needs to be considered. AuNPs were used as a case study due to their rising medical applications and therefore increasing probability to reach the sewer and STP. The results can provide significant input for the interpretation of results from the regulatory point of view. To deliver these objectives, the general changes of the microbial population in activated sludge and its influence on the degradation activity (dissolved organic carbon (DOC) and inorganic nitrogen) using freshly collected sludge from the municipal STP in an artificial test system as a model STP in accordance with OECD 303A (2001) were assessed. Additionally, we evaluated the potential impact of AuNPs and its dispersant on the microbial composition and the overall impact on the function of the STP in terms of DOC degradation and nitrogen removal to observe if an assessment based on functional properties is sufficient. The bacteria composition in our study, evaluated at a class level, revealed commonly described environmental bacteria. Proteobacteria (β, α, δ) accounted for more than 50% but also nitrifying bacteria as Nitrospira were present. Our results show that mainly within the first 7 days of an acclimatization phase by addition of synthetic sewage, the bacterial community changed. Even though AuNPs can have antibacterial properties, no adverse effects on the function and structure of the microorganisms in the STP could be detected at concentrations of increased modeled PEC values by a factor of about 10,000. Complementary to other metallic nanomaterials, gold nanomaterials also sorb to a large extent to the activated sludge. If activated sludge is used as fertilizer on agricultural land, gold nanoparticles can be introduced into soils. In this case, the effect on soil (micro)organisms must be investigated more closely, also taking into account the structural diversity.

Current state, population structure and population dynamics of rare plants under economic and recreational use of natural-territorial complexes in the Middle Volga basin (Russia)

The article summarizes the results of studies on the population structure and population dynamics of rare plants of the steppe and forest-steppe zones of the European part of Russia. Conservation of representatives is mainly ensured by the creation of protected areas and the inclusion in the Red Books. Four groups of species by peculiarities of ontogenetic structure and type of cenopopopulations according to the “delta-omega” criterion were determined. Most species are characterized by a mature type of cenopopopulations with a predominance of generative individuals. Long-term studies allowed us to establish that most of the rare species of the region have maintained their numbers. However, 30 representatives, the number of which has noticeably decreased, need to strengthen the conservation measures. The studies are of interest in the development of conservation measures, identifying the current ecological state of natural-territorial complexes under economic and recreational pressure, determining the categories of rarity of species, justifying the inclusion or exclusion of them from the Red Books.