Farmland Populations Research Articles

Evolution of competitive traits changes species diversity in a natural field.

Studying the interaction between evolutionary and ecological processes (i.e. eco-evolutionary dynamics) has great potential to improve our understanding of biological processes such as species interactions, community assembly and ecosystem functions. However, most experimental studies have been conducted under controlled laboratory or mesocosm conditions, and the importance of these interactions in natural field communities has not been evaluated. In this study, we focused on the contemporary divergence of a competitive trait (the height-width ratio) of an annual grass Eleusine indica between urban and farmland populations and investigated how trait evolution affects ecological processes by transplanting E. indica individuals from lineages with different trait values into semi-natural grassland. The competitive trait of the transplanted individuals not only affected their own growth and fitness, but also affected the vegetative growth of the competing species and the species diversity. These results indicate that the evolution of competitive traits, even in a single species, can influence the community species diversity through changes in interspecific interactions. Eco-evolutionary interactions therefore play a crucial role in natural field environments. Our results suggest that understanding intraspecific variation in competitive traits driven by rapid evolution is essential for understanding interspecific competitive interactions, community assembly and species diversity.

Contemporary adaptive divergence of plant competitive traits in urban and rural populations and its implication for weed management

Abstract Competition among neighbouring plants plays essential roles in growth, reproduction, population dynamics, and community assembly, but how competition drives local adaptation and the traits underlying the adaptation remain unclear. Here, we focused on populations of the aggressive weed Digitaria ciliaris from urban and rural habitats as low‐ and high‐competition environments for light resources and examined how competitive interaction drove contemporary adaptive divergence of competitive traits. To examine local adaptation to different competitive environments in D. ciliaris and the specific traits that have been selected for, we compared growth rate and competitive traits in plants from farmland and urban populations between high‐ and low‐competition treatments. Furthermore, we conducted a field tillage experiment with drone (unmanned aerial vehicle) monitoring to examine the possibility that trait evolution in farmland habitats might influence weed management practices in crop fields. Plants from farmland populations had higher growth rates than plants from urban populations in high‐competition treatments, and vice versa in low‐competition treatments. Among populations, those with larger height/width ratios (farmland populations) were more tolerant of above‐ground competition in high‐competition treatments, but among individuals, those with larger ratios had lower growth rates in low‐competition treatments. More plants from farmland populations, which had thicker stems (and larger height/width ratios), survived after experimental tillage than plants from urban habitats with thinner stems. Synthesis. Our study empirically demonstrated adaptive divergence in competitive traits in above‐ground competitors and its underlying traits. Moreover, contemporary adaptive divergence between urban and rural plant populations has practical implications for weed control. The urban–rural model system can thus contribute to both basic and applied research in plant evolutionary ecology. Further research is required to understand adaptive divergence in plants between urban and rural environments, and the traits underlying the adaptation, not only above‐ground but also below‐ground.

Short seed‐dispersal distances and low seedling recruitment in farmland populations of bird‐dispersed cherry trees

Summary In Central Europe, many plant populations are patchily distributed in human‐modified landscapes and depend on animal vectors for seed dispersal. To predict seed‐dispersal distances and locations of seeds of wild cherry trees (Prunus avium L.) in forest and farmland habitats in a human‐modified landscape, we integrate movement data and seed regurgitation times of the Common Blackbird (Turdus merula L.) in a simulation model. We performed feeding trials with Common Blackbirds and wild cherries to determine the distribution of regurgitation times. We captured 32 male blackbirds and equipped them with radio tags to follow their movements in forest and farmland habitats. To simulate the movement of cherry seeds through the landscape, we combined the distribution of regurgitation times with bird movement data and modelled seed‐dispersal distances and locations of seed deposition for forest and farmland birds. According to our simulations, more cherry seeds were deposited under foraging trees in farmland (20.8%) than in forest populations (9.5%). Median seed‐dispersal distances (50.8 vs. 68.2 m) and the proportion of long‐distance dispersal events (distances > 100 m) were predicted to be lower in farmland (14.9%) than in forest populations (28.2%). In the model, forest‐dwelling blackbirds dispersed more cherry seeds into suitable habitat (98.7%) than farmland blackbirds (85.4%). In both habitats, seed deposition in suitable habitat was much higher than expected from the proportion of suitable habitat within blackbirds' home ranges, indicating directed dispersal. To test whether differences in seed‐dispersal locations were related to recruitment success, we recorded seedling densities in farmland and forest populations of P. avium and determined survival probabilities of seedlings. Seedling densities and survival were much lower in farmland than in forest populations, even accounting for strong environmental effects on seedling recruitment. Synthesis: Our findings show that behavioural differences of animal seed dispersers between habitat types can result in substantial changes in seed‐dispersal distances and locations in human‐modified habitats. These changes in seed‐dispersal services for bird‐dispersed plant species may be related to reduced seedling recruitment in farmland populations making such populations prone to extinction in the long term.

Presence of allochronic populations of the white grub beetle Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) on Ishigaki Island, Japan

To investigate the seasonal prevalence of Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scarabaeidae), synthetic sex pheromone traps were placed on Ishigaki Island in 2008 and 2009. One population is known to occur in the forest and fly for mating from early March to early April. The trap data revealed a second population in the farmland that flew for mating much earlier (mid-January to late February) than did the other population, indicating the presence of allochronic populations. Adults of the farmland population were caught throughout the sugarcane-grown area on the island, whereas those of the forest population appeared to be limited to the forest area. The temporal pattern of trap catches of each population was generally the same between 2008 and 2009. Relatively large trap catches were observed in the west central plane area and a small northern area of the northeastern peninsula of the island. These results suggest that, although it has not caused any damage to agricultural crops on this island, this beetle might be a potentially serious pest of sugarcane crops in the future, as reported on another island of Okinawa.

Assessing the implications of the loss of set‐aside for farmland birds

Between 1988 and 2007, set‐aside, a European Commission production control measure, took an average of 10% of arable farmland in the EU out of production each year. In 2007, the set‐aside rate was set to 0% and the scheme was later abandoned altogether. By assessing associations of farmland birds with set‐aside and quantifying the extent of set‐aside loss, this study aims to assess the implications of set‐aside loss for farmland bird conservation. During the lifespan of set‐aside, a large number of studies assessed the biodiversity value of set‐aside and other agricultural crops and habitats. Where possible we considered measurable benefits of set‐aside. However, some studies did not specify the type of set‐aside and in some cases set‐aside fields were grouped with cereal stubble fields. In these cases, we took the pragmatic approach of assessing the value of generic stubble fields as a conservative minimum estimate of the value of set‐aside fields. A re‐analysis of data from 30 intensive studies demonstrates that farmland bird densities tended to be higher on set‐aside than on either cereal or oilseed rape crops. Without mitigation, these are the two crops likely to replace most set‐aside fields. We estimate that 26–52% of the farmland populations of key granivorous passerines were present on stubble fields, giving an indication of the proportion of birds likely to be present on set‐aside fields within this broader category. An extensive survey of lowland farmland during winters 1999/2000, 2000/2001 and 2002/2003, repeated in February 2008, showed a doubling of the number of 1‐km squares with no stubble and a halving of the number of squares with more than 10 ha of stubble. After set‐aside abandonment, 72% of squares had no stubble in the important late winter period, confirming that many of the former stubble fields were retained as set‐aside. A simple correlative model suggests that this could cause a small increase in the rate of decline of Skylark Alauda arvensis and Yellowhammer Emberiza citrinella populations, assuming causal links between stubble area and demography. However, even if this assumption cannot be supported, these results clearly indicate that a significant proportion of some farmland bird populations will need to find alternative breeding and foraging habitats.

Contrasting infection frequencies of Neotyphodium endophyte in naturalized Italian ryegrass populations in Japanese farmlands

Abstract Neotyphodium endophytes often confer benefits to their host grasses and may enhance invasiveness of some grasses. The knowledge of infection frequencies of endophytes among invading weed populations is necessary to understand the relationships between endophyte infection and invasiveness. Here we present data on infection frequencies of Italian ryegrass (Lolium multiflorum Lam.), an important weed in some farmlands in Japan, persisting in contrasting farmlands: a terraced paddy field and a wheat‐soybean double‐cropped field in the western region of Shizuoka prefecture, Japan. The terraced paddy site is a mosaic of several landscape elements such as paddy fields, levees, fallow and abandoned fields, with a high percentage of non‐crop area. Rice (Oryza sativa L.) has been cultivated for more than a decade with no application of chemical fertilizers, pesticides and fungicides. The wheat‐soybean field is characterized by the aggregation of large‐scaled fields that were originally reconstructed paddy fields, showing a low percentage of non‐crop area. Wheat and soybean have been grown as winter and summer crops, respectively, using chemical fertilizers and herbicides. We examined the presence or absence of endophytes in a total of 1200 seeds sampled from the two Italian ryegrass populations. The terraced paddy population exhibited a markedly high infection frequency (91.0%), due possibly to selective feeding of non‐infected seeds by insects. In contrast, the wheat‐soybean farmland population showed almost no infection (1.1%), whereas the putative source of the invasion in the proximity exhibited a relatively high infection rate (64.4%). Such a micro‐scale variation in infection frequencies may be attributable to a loss in endophyte viability within the wheat‐soybean field. The findings suggest that endophyte infection frequency may markedly differ among the Italian ryegrass populations even within the same region, presumably depending on the abundance of the seed‐eating insects, farmland management regimes and/or environmental conditions such as soil humidity.

Habitat selection by Ortolan Buntings Emberiza hortulana in post‐fire succession in Catalonia: implications for the conservation of farmland populations

The Ortolan Bunting Emberiza hortulana is a long‐distance migrant that has suffered major population declines across much of its European breeding range. While northern populations are bound largely to farmland, Mediterranean populations are largely confined to habitats subject to recurrent wildfires. Habitat selection of the Ortolan Bunting was assessed in a recently burnt area in Catalonia at landscape and habitat scales. A Zero‐inflated Poisson procedure was used to model the abundance of birds in relation to landscape and habitat variables. The most parsimonious landscape model predicted the highest abundance on south‐facing slopes, with a gradient above 10°. The most parsimonious habitat model showed a positive quadratic effect of bare ground and regenerating oak Quercus spp., with predicted optima for abundance around 20–30% and 20% cover, respectively. There was a clear relationship between predicted abundance of the Ortolan Bunting and post‐fire regenerating oak shrubs. South‐facing, moderately sloping areas were favoured and bare ground was a key feature of the species’ habitat. A matrix combining patches of sparse oak shrubs and patches of bare ground appears to be the optimal breeding habitat in the Mediterranean. The maintenance or provision of similar habitat features, especially patches of bare ground, may prove crucial for the conservation of rapidly declining Ortolan Bunting populations on farmland across temperate Europe.

Genetic structure, relatedness and helping behaviour in the yellow mongoose in a farmland and a natural habitat

AbstractThe yellow mongoose Cynictis penicillata is a facultatively social species and provides an opportunity to study the evolution of social behaviour. We examined genetic structure, relatedness and helping behaviour in the yellow mongoose in natural habitat in the Kalahari Desert, where the species lives in small family groups of up to four individuals and shows no cooperative breeding; and in farmland in the Western Cape Province of South Africa, where they live in larger groups of up to 13 individuals, engage in numerous social interactions and show cooperative breeding. The farmland population showed significant inbreeding, and lower genetic variability than the desert population, but there was no evidence of a recent population bottleneck. The genetic relatedness between individuals within social groups and that between future potential helpers and pups were higher in the farmland population than in the desert population. However, based on a limited sample, helping effort (in the farmland population) was not preferentially directed towards kin. Thus, the origin of helping in the farmland population is consistent with kin selection, but in the absence of kin discrimination, future research should investigate whether long‐term breeding opportunities or group augmentation contribute to maintaining cooperative breeding in this population.

Low frequency of anti-acetylcholinesterase pesticide poisoning in lesser and Eurasian kestrels of Spanish grassland and farmland populations

Lesser kestrel Falco naumanni and Eurasian kestrel Falco tinnunculus are two small raptor species commonly breeding in open agro-pastoral systems that have suffered a dramatic decline in their populations during the past few decades due to changes in land use. Direct intoxication by chemicals used in farming has been one of the causes proposed promoting population declines in both species. However, there have been no studies exploring the degree of kestrel intoxication at individual or population levels in the wild. We investigated the inter-population variation in blood levels of acetylcholinesterase (AChE) in nestlings of Spanish Lesser and Eurasian kestrels. AChE was used as an estimator of the degree of organophosphorus (OP) and/or carbamate (CB) exposure or intoxication. In addition, we measured the albumin–globulin ratio (A/G) as an index of general health status. We found only extremely low AChE levels in lesser kestrels from one of the seven studied populations. In addition, we did not find differences in nestling AChE levels between pastoral and agricultural habitats. Furthermore, the present study revealed that two of the seven lesser kestrel populations are suffering from poor health conditions, in one case due to OP–CB poisoning, and the other possibly due to a pathogen infection as suggested by the low A/G ratio observed. Thus, our study suggests that, in general, OP and/or CB pesticide poisoning in traditional agro-pastoral systems in Spain is not currently an important conservation factor for either Lesser or Eurasian kestrels chicks.

Demographic and environmental causes of the decline of rural Song Thrushes Turdus philomelos in lowland Britain

We review current knowledge of demographic mechanisms and environmental factors implicated in the population decline of Song Thrushes Turdus philomelos in rural Britain since the mid‐1970s, and present new analyses of regional variation in population changes. Increased mortality during the first year of life (from fledging to recruitment) is highlighted as a potential demographic mechanism having driven the population decline, while Song Thrushes in a rapidly declining farmland population were making too few nesting attempts to sustain local numbers. Breeding Song Thrushes are strongly associated with non‐cropped habitats such as woodland edge, field boundaries, gardens and scrub; they make substantial use of grassland, but avoid cereals when foraging. Earthworms constitute a key component of Song Thrush diet and the availability of this prey is strongly influenced by moisture levels in surface soils. Several lines of evidence suggest that dry surface soils during summer are deleterious to the productivity and survival of Song Thrushes, and regional variation in the rates of population change in Britain during 1970–86 was negatively correlated with the extent of under‐field drainage on farmland (the main function of which is to promote the drying of surface soils). Increasing dryness of agricultural soils and the loss of grassland from eastern arable counties have probably both contributed to the declines of rural Song Thrushes in Britain. Loss of hedgerows and scrub, and the degradation of woodland may also have contributed to population declines but the role of predators remains unclear. Recovery of rural Song Thrush populations requires challenging new policy initiatives that should aim to restore nesting cover (scrub and woodland understorey), grazed grassland in arable‐dominated areas and damper soils in summer.

Habitat selection by song thrushes in stable and declining farmland populations

Summary Losses of farmland birds from the wider countryside have become a major conservation issue in the UK and Europe. Song thrush Turdus philomelos populations in lowland rural Britain declined by approximately 70% during 1970–95, most severely on intensively managed arable farmland. Comparison between a stable population on mixed farmland and a rapidly declining population on arable farmland revealed fewer nesting attempts each summer by birds in the declining population, and annual productivity was insufficient to maintain local population density. Inadequate food resources were the most plausible cause. We compared breeding season habitat selection (using radio‐telemetry) and earthworm availability (a major component of summer diet) for song thrushes in the same two farmland populations. Territory settlement in the mixed farmland landscape involved the selection of field boundaries and woodland and the avoidance of arable crops. Field boundaries and gardens were selected in the arable landscape, while arable break crops and small areas of woodland were avoided. Habitat selection (intensity of usage) did not change through the breeding season and did not differ between study areas. Scrub, woodland edge, wet ditches and bare soil in gardens were preferred foraging habitats, while cereals were avoided. Habitat utilization (amount of usage) differed markedly between study areas. Woodland and grassland accounted for 53% of all habitat usage in the mixed farmland landscape compared with just 13% in the arable landscape. Gardens and arable crops were more heavily utilized in the arable landscape, accounting for 58% of all usage compared with 22% in the mixed landscape. Earthworm availability declined markedly between April and June as surface soils dried out. Lower earthworm availability in the arable landscape was associated with more rapid and pronounced drying of surface soils. Synthesis and applications. Lack of woodland and grassland, and the faster drying of surface soils in the arable landscape, combined to limit the availability to thrushes of key summer invertebrate prey. Loss of hedgerows, scrub and permanent grassland with livestock, and the wide‐scale installation of under‐field drainage systems, have probably all contributed to the decline of song thrushes on UK arable farmland. New agri‐environment measures may be needed to provide the nesting cover adjacent to invertebrate‐rich damp soils that song thrushes require to sustain annual productivity.

Summer diet and body condition of Song Thrushes Turdus philomelos in stable and declining farmland populations

Summer diet and body condition were compared in two farmland Song Thrush Turdus philomelos populations in south‐east England. One population on mixed farmland was stable and the other on arable farmland was rapidly declining. Summer diet was dominated by earthworms, snails, beetles and insect larvae (mainly Coleoptera and Lepidoptera). In both populations there was a pronounced seasonal decline in the quality of the diet, with preferred earthworms dominating prey items during March–April and snails dominating during June and July. Dry weather during late summer was associated with reduced proportions of earthworms and snails, and increased proportions of spiders in the diet, and dry soil conditions had a weak negative influence on the body weights of chicks (in the arable population) and adults. Despite a tendency for earthworms to constitute a higher proportion of the diet in the stable population, and for snails to constitute a higher proportion of the diet in the declining population, the body condition of chicks and adults appeared to be unrelated to diet composition and did not differ between study populations. Changes in agricultural practices have probably caused a major reduction in the availability of key summer food resources for Song Thrushes on lowland farmland, and we speculate that breeding thrushes mitigate the impacts of food shortage on chicks by confining their nesting attempts to localities and periods where invertebrate food resources are adequate to raise a brood of young.

Widespread local house-sparrow extinctions.

House-sparrow populations have declined sharply in Western Europe in recent decades, but the reasons for this decline have yet to be identified, despite intense public interest in the matter. Here we use a combination of field experimentation, genetic analysis and demographic data to show that a reduction in winter food supply caused by agricultural intensification is probably the principal explanation for the widespread local extinctions of rural house-sparrow populations in southern England. We show that farmland populations exhibit fine-level genetic structuring and that some populations are unable to sustain themselves (sinks), whereas others act as sources.

SPATIAL SYNCHRONY IN POPULATIONS OF BIRDS: EFFECTS OF HABITAT, POPULATION TREND, AND SPATIAL SCALE

The degree of synchrony between populations is critical for their dynamics at large spatial scales. Population synchrony has been assessed for only a few species of vertebrates, most of them have largely fluctuating populations with multiannual cycles. We investigated the intensity and spatial extent of synchrony among populations of birds in Britain. The data analyzed ran from 1962 to 1995 at more than 1000 local sites and concerned 60 species. For each species, we measured the intensity of synchrony among local popu- lations using the cross-correlation function (CCF) and assessed its spatial extent. We tested for differences in these two measures with respect to habitat. We also assessed the potential influence of long-term trends in population synchrony. By aggregating the sites in regions and estimating an index for each region, we measured synchrony at a large spatial scale. In general, we found that synchrony was low between populations of British birds. All but one species with the strongest level of synchrony show a pronounced long-term decline. The mean CCF was significantly correlated with the mean abundance of each species in the Common Birds Census (CBC) sites, suggesting that the more abundant species have more synchronous populations. Significant differences in synchrony between habitats were found in 25 species; synchrony was stronger in farmlands compared to woodlands for 22 species. The same result was observed both at the intra- and interspecific levels. This may be the result of national change in agricultural practice affecting all farmland populations. Our cross-scale analysis showed that synchrony is a scale-dependent phenomenon. Our study is the first to focus on a large number of noncyclic species, and it suggests that synchrony is weaker for these species than for those with widely fluctuating cyclic populations. This is in agreement with some studies on synchrony of insects. Synchrony in natural populations seems to be determined by complex interactions between abundance, population variability, species characteristics, and demographic mechanisms. A general pattern emerging from our study and others is that population synchrony is more intense during declines.

The importance of variation in the breeding performance of seed‐eating birds in determining their population trends on farmland

Summary 1. Changes in agriculture have been linked to widespread declines in farmland bird populations. One approach to the identification of the causes of observed population changes is to investigate historical changes in national demographic rates. 2. We analysed the British Trust for Ornithology’s nest records database to investigate whether long‐term farmland population trends could have been driven by changes in several components of the annual breeding performance of 12 granivorous bird species. Clutch size, brood size, chick : egg ratio and daily nest failure rates were analysed with respect to blocks of years during which abundance (as measured by the Common Birds Census) was increasing, stable or declining. The individual components of breeding performance were combined to provide estimates of the production of fledglings per breeding attempt. 3. Most species’ population declines were not associated with poor breeding performance per attempt. Effects of environmental change on this parameter therefore cannot be a general mechanism behind the major population declines seen. 4. A fall in linnet Carduelis cannabina fledgling production per attempt, driven primarily by increased nest failure rates during the egg period, represented the strongest evidence for an important effect of breeding performance on abundance. This change could have driven the principal population decline (1975–86) for this species. 5. Conversely, at least for the declining turtle dove Streptopelia turtur, skylark Alauda arvensis, tree sparrow Passer montanus, yellowhammer Emberiza citrinella and corn bunting Miliaria calandra, breeding performance per attempt was higher while populations declined. 6. Variation in annual survival and fledgling production per breeding attempt alone could not explain changes in abundance for at least seven species. This may suggest that changes in post‐fledging survival rates and/or the number of breeding attempts per year could have been important. 7. Management to improve over‐winter survival may be critical in reversing the population trends of most declining species, but such management might still best be directed at the breeding season. Post‐fledging survival rates and the number of breeding attempts made within a season are little‐studied demographic variables that are high priorities for future research and long‐term monitoring.

The Effect on a British Wild Rabbit Population (Oryctolagus cuniculus) of Manipulating Myxomatosis

1. Myxomatosis no longer has the dramatic impact on rabbit numbers of the original outbreaks in 1953-55. The influence of the disease on rabbit numbers 25.30 years later was investigated by twice reducing and then restoring the prevalence of myxomatosis in a farmland population. 2. Insecticide was used for 2 years to reduce the numbers of rabbit fleas, the main vector of the disease. Flea numbers were subsequently increased by systematic reintroductions over a further 2 years and the sequence was then repeated. 3. Changes in the prevalence of myxomatosis followed the changes in flea numbers. 4. Rabbit numbers increased by two- to threefold during the flea reduction periods, and fell in the reintroduction periods

Qualitative Changes in Populations in Unstable Environments

AbstractInactive moths of Malacosoma pluviale (Dyar) oviposit near their birthplaces, and most of their offspring also are inactive. More active moths can travel farther before they oviposit, and always have a higher proportion of vigorous individuals among their progeny.Such polymorphism allows the insect to cope with environmental diversity; e.g., inactive residents exploit favourable habitats, and active migrants colonize more severe habitats, or replenish the vigour of other populations.Because the most active moths usually export the most vigorous progeny, the population left behind becomes less vigorous during successive generations. This steadily decreasing vitality eliminates local populations that are not replenished by vigorous immigrants.Qualitative changes in Malacosoma populations follow this basic pattern, but the rate of deterioration is affected by the habitat. Departing migrants fly too high to be stopped by small trees in farmland, bur many are stopped near their source by tall trees in forests. Deterioration therefore is slower in forests. Forests also delay return migration to nearby farmlands, and thus allow some farmland populations to deteriorate unchecked.In a fluctuating climate, the size of the area tolerable for the species varies annually. When it begins to expand, the vigorous progeny of active moths can take immediate advantage of slight local improvements. Consequently, they are the first to exploit each marginal habitat that becomes tolerable. But while better climate persists, some less active descendants of these pioneers appear in all occupied habitats.When the regional climate deteriorates, the tolerable area contracts, and most marginal populations are totally destroyed. Moreover, even within the contracted tolerable area, the harsher climate becomes intolerable for any deteriorated stock. In the next generation, therefore, the only regional survivors are vigorous colonies deposited in the tolerable area by some of the few migrants that escaped the widespread destruction of the preceding generation in the margins. Their descendants recolonize depopulated sections of the refuge, and so preserve the species in the region while the climate remains severe.