Regional population viability of grassland songbirds: Effects of agricultural management

Although population declines of grassland songbirds in North America and Europe are well-documented, the effect of local processes on regional population persistence is unclear. To assess population viability of grassland songbirds at a regional scale (∼150,000 ha), we quantified Savannah Sparrow Passerculus sandwichensis and Bobolink Dolichonyx oryzivorus annual productivity, adult apparent survival, habitat selection, and density in the four most (regionally) common grassland treatments. We applied these data to a female-based, stochastic, pre-breeding population model to examine whether current grassland management practices can sustain viable populations of breeding songbirds. Additionally, we evaluated six conservation strategies to determine which would most effectively increase population trends. Given baseline conditions, over 10 years, simulations showed a slightly declining or stable Savannah Sparrow population (mean bootstrap λ = 0.99; 95% CI = 1.00-0.989) and severely declining Bobolink population (mean bootstrap λ = 0.75; 95% CI = 0.753-0.747). Savannah Sparrow populations were sensitive to increases in all demographic parameters, particularly adult survival. However for Bobolinks, increasing adult apparent survival, juvenile apparent survival, or preference by changing habitat selection cues for late-hayed fields (highest quality) only slightly decreased the rate of decline. For both species, increasing the amount of high-quality habitat (late- and middle-hayed) marginally slowed population declines; increasing the amount of low-quality habitat (early-hayed and grazed) marginally increased population declines. Both species were most sensitive to low productivity and survival on early-hayed fields, despite the fact that this habitat comprised only 18% of the landscape. Management plans for all agricultural regions should increase quality on both low- and high-quality fields by balancing habitat needs, nesting phenology, and species’ response to management.     

Managing successional species: Modelling the dependence of heath fritillary populations on the spatial distribution of woodland management

Species that persist on a shifting mosaic of successional habitat offer particular challenges to conservation, to monitoring methods, and to population dynamic modelling. The conservation of the heath fritillary butterfly (Melitaea athalia) in woodland in England, for example, depends on the creation of woodland clearings by coppicing (rotational cutting). We have developed a simulation model to assist in the conservation of such populations, called MANAGE. We have parameterised the model for the M. athalia population in the Blean Woods in Kent, and used it to answer several management questions. We find that: (1) simulations predict that the observed rates of coppicing will not be enough to meet existing conservation (Biodiversity Action Plan) targets, except when the most generous modelling assumptions are made; (2) the greatest uncertainty in the model outcome arises from uncertainty in the colonisation parameters; (3) in the worst case scenario (using the most pessimistic model assumptions), a population would require 2.3% of the Blean Woods to be coppiced each year, which is around double the currently-observed rate; (4) the four management units of the Blean where coppicing is practised are not independent metapopulations– they support each other; and (5) to sustain a population in a smaller landscape would require less coppicing overall, but more as a percentage of the landscape. This modelling approach may prove useful in the development of conservation management plans for other species that inhabit successional habitats.     

The status of the health fritillary butterfly Mellicta athalia Rott. in Britain

An extensive survey was made of known and potential sites of the heath fritillary butterfly Melllicta athalia Rott. in Great Britain in 1980. The size of every colony found was measured and information obtained on its habitat preferences and larval foodplants. Details of all the sites that still support this butterfly are summarised and its habitat requirements are assessed.The survey confirmed that the heath fritillary is probably the most endangered resident butterfly in Britain. It has declined severely in recent years and is now restricted to five sites in SW England and to three woodland blocks in E Kent. Thirty-one colonies were discovered (6 in the SW, 25 in Kent), but 24 of these contained fewer than 200 adults on the peak day. Moreover, several occurred close to larger populations and may only be offshoots that would not be viable on their own.The heath fritillary has different habitat requirements in SW England and Kent, although in both regions it needs sunny sheltered woodland that is at an early stage of succession or regeneration. Such habitat is ephemeral and must be generated continuously within fairly small areas if it is to be utilised, for the butterfly rarely flies long distances. Nearly all documented extinctions have been caused by a loss of suitable habitat from the locality, for this is only occasionally created by most modern forms of silviculture. In Kent, the heath fritillary survives mainly in the ever-decreasing areas where traditional coppicing has continued, but the future of this practice is now in doubt. Few colonies survive in SW England, although some are now being managed specifically to safeguard the butterfly.     

Breeding system and inbreeding depression in the clonal plant species Knautia arvensis (Dipsacaceae): implications for survival in abandoned grassland

Larger clonal sizes observed in abandoned than in managed grassland could result in increased geitonogamy in Knautia arvensis. The species was investigated for self-compatibility, seed set without pollinators, and inbreeding depression in a greenhouse experiment. Seed set was equivalent in hand-selfed and hand-outcrossed plants (c. 53%), indicating full self-compatibility. Seed set was low (2.8%) in caged, unmanipulated flower heads. There was no significant difference in seed weight, germination, and survival between selfed and outcrossed progeny. Juvenile biomass was significantly lower in selfed than in outcrossed progeny (on average 45% lower). Cumulative fitness calculations for germination, survival, and juvenile biomass showed that the mean inbreeding depression was 58% in offspring produced by selfing. The results suggest that in K. arvensis, which is protected against self-pollination within flower heads through protandry, the likely mechanism for selfing is via geitonogamy among flower heads. Geitonogamy among ramets within the larger clones observed in abandoned grassland could reduce offspring viability in K. arvensis since the fitness of selfed offspring was low. Inbreeding depression could therefore add to the recruitment problems experienced by plants in abandoned grassland, both in K. arvensis and probably in other clonal grassland species, depending on their growth structure and breeding system.     

The re-expansion and improving status of the silver-spotted skipper butterfly (Hesperia comma) in Britain: a metapopulation success story

Many specialist species are declining as a result of habitat loss and fragmentation, such that conservation actions typically aim to stem rates of decline rather than bring about genuine recovery. Here, we document the recovery of a species from former population refuges. An extensive survey of the entire British range of Hesperia comma, conducted in 2000, recorded over three times the number of tetrads (2 km × 2 km grid squares) occupied in 1982. This was accompanied by a fourfold increase in the number of populations and a 10-fold increase in the habitat area occupied. The improving status of H. comma is the product of good habitat management, recovering rabbit populations and climate warming, which have improved the quality, and increased the availability, of suitable habitat. This has enabled remnant metapopulations to expand, via distance-dependent colonisation, through large networks of habitat. Metapopulation recovery in H. comma demonstrates that landscape-scale conservation can be successful.     

When is a habitat not a habitat? Dramatic resource use changes under differing weather conditions for the butterfly Plebejus argus

A key to conserving organisms is identification of the habitat bounds and essential resources within them. In population studies (metapopulations) of phytophagous arthropods it is tacitly assumed that habitat bounds portray short-term stability and that habitat is largely synonymous with hostplant areas or with a single vegetation unit comprising hostplants; structural components are usually ignored. We test these assumptions by monitoring the behaviour and relative abundance of Plebejus argus (L.) (Lepidoptera: Lycaenidae) in relation to changing weather conditions in two patches of a North Wales metapopulation for the butterfly. Our findings confirm the importance of structural habitat components. P. argus density is higher in the vicinity of shrubs which are used for roosting, resting, basking, mate location and shelter. A dominant proportion of the population adopts shrub areas in cooler, cloudy and windy weather. In warmer, sunnier and calmer conditions, the butterfly spends longer in flight and moves out onto calcareous heath dominated by hostplants. In doing so, an increasing, even dominant, proportion of the population occupies exposed slopes adjacent to and above shrub covered areas associated with the hostplant. In effect, the habitat bounds appear to change with conditions on scales of days and hours. What part of a landscape may be defined as a habitat, and what part of it may appear to be most important for an organism, depends on just when and where surveys are carried out. We argue that for correct delineation of habitats attention needs to be given to resource use in different conditions. In the face of enhanced global warming, a broad view should be taken of arthropod habitats that considers the resources required for varying conditions.     

Effects of community-level grassland management on the non-target rare annual Agalinis auriculata

The objective of grassland management is to maintain keystone species, as well as species diversity, to promote a particular community structure, or to preserve specific ecosystem processes. Studies of grassland management rarely ascertain the effects on rare plant species, although conservation plans for rare herbaceous plants often recommend habitat management as well as restoration activities. Indeed, conservation biology has evolved from a relatively species-specific discipline into one more focused on larger scale issues such as ecosystem function, community composition and habitat restoration. Few studies have tested whether species of concern are adequately managed with a community or ecosystem-level approach. In this study, we evaluate whether community-level management of white-tailed deer and woody brush improves the viability of the rare annual plant species, Agalinis auriculata (Earleaf false foxglove; Orobanchaceae). Reducing deer browse and removing brush each positively affect plant vital rates. Brush removal increases the proportion of plants that reach the largest size class. Reducing deer browse increases the fertility of plants, particularly those in the largest size class. We report on demographic matrix models created with data from five populations of A. auriculata studied across 4 years. We find that both management activities positively affect the non-target plant species and are, in fact, necessary for A. auriculata to persist. Conservation of A. auriculata at our study sites requires both reducing the density of white-tailed deer and brush removal. Our study demonstrates that management at the community and ecosystem levels can be compatible with conservation goals at the species and population levels.     

Future prospects for the rare, late-flowering Gentianella germanica and Gentianopsis ciliata in Dutch nutrient-poor calcareous grasslands

We discuss the population biology of two calcareous grassland gentians, Gentianella germanica and Gentianopsis ciliata, in relation to the habitat management currently practiced in The Netherlands. There, at the margin of their range, both species are rare. Gentianella germanica persists on six remaining locations, whereas Gentianopsis ciliata, with two populations, is nearly extinct. Gentianella germanica is a strict biennial, Gentianopsis ciliata an iteroparous perennial. Both species depend on insects for seed production and suffer from low insect visitation. Pollination experiments in one Dutch population demonstrated that Gentianopsis ciliata is self-compatible, but hardly sets any seed under natural conditions due to pollen limitation. The low reproductive success of both species is partly due to the low pollinator densities at their late flowering time, partly caused by the small population size of the gentians themselves, and partly a result of mowing too early. The latter has destroyed the seed crop of several subsequent years in one population of Gentianopsis ciliata and some of Gentianella germanica. In Gentianella germanica, the early mowing and low insect visitation seems to have resulted in selection of less herkogamous and consequently more autofertile individuals. The perspectives for Gentianopsis ciliata are currently extremely poor in The Netherlands. Under the present circumstances, extinction will most likely occur within 10-20 years. Population reinforcement (seeding, artificial cross-pollination with nearby populations) should be considered if we want to conserve this species. For both gentians, but also of other flagship species of nutrient-poor calcareous grasslands, the total grassland area needs to be enlarged and must constitute an interconnected network of reserves. The traditional management method, sheep grazing, is to be preferred over mowing, but only if the flock visits each grassland patch or reserve for only a short time of less than a day, and with intervals of more than 2 weeks between visits. If mowing is preferred for other reasons, it should be done rotationally, and not before October.     

Higher breeding densities of the threatened little bustard Tetrax tetrax occur in larger grassland fields: Implications for conservation

Previous studies have found that densities of little bustard Tetrax tetrax breeding males tend to be higher in areas with smaller agricultural fields, presumably due to increased habitat diversity. However, exceptionally high densities have been found in large grassland fields in Portugal, which suggests that the influence of field size varies geographically, and that the role of this factor is not yet fully understood, despite its importance as a key management issue.We studied how field size, together with vegetation structure, influences the presence and density of breeding little bustards in a region of southern Portugal. Fifty-four grassland fields were sampled in 2007 and another 29 in 2008, with sizes ranging from 23 to 172 ha. A total of 183 breeding males were found in 47 of these fields, reaching densities of up to 37 males/100 ha. A higher probability of occurrence of breeding males was found in larger fields with a vegetation height below 40 cm and field size alone explained 46% of the variability in male density. These results suggest that larger continuous areas of suitable habitat attract many males, most likely as a consequence of their lek mating system. We conclude that conservation efforts, in a landscape context of large farm sizes, should: (1) be channelled to farms with large fields; (2) ensure adequate livestock grazing to create suitable habitat and (3) promote management at a landscape level to ensure the most continuous grassland habitat patches possible.     

Importance of the seed bank for population viability and population monitoring in a threatened wetland herb

Although demographic models have become increasingly important tools in plant conservation, few models have considered the implications of seed banks for population persistence. Based on a 15-year study of the threatened herb, Helenium virginicum, we created a stage-class transition matrix to model the population dynamics of the plant. Our goal was to determine the role of the seed bank in population persistence and in the design of monitoring programs for the plant. Using data from marked plants, a long-term study of seed viability, and a seed bank census, we created a deterministic model and three stochastic models. The stochastic models were a model in which yearly correlations among parameters were retained, a model in which parameters were uncorrelated, and a model in which parameters were derived from log-normal distribution. We also constructed a fourth model in which we assumed a minimum seed lifetime consistent with the seed viability data. Both elasticity and perturbation analysis suggested that seed survival within the seed bank had by far the largest effects on the population growth rate (λ), with 47-64% of the change in λ being controlled by seed survival. Correlations among life history parameters had little effect on λ in the original models, but substantially reduced λ (from 0.97 to 0.86) when seed survival was limited. Given the importance of the seed bank and the high yearly variability in adult plant density, we used simulations to compare power to detect declines with seed bank samples versus censuses of adult plants. The power of adult plant censuses was extremely low (13-22%). The power of seed bank censuses was substantially higher (48-59%), but was limited by large pulses of recruitment to the seed bank in good years. Power was only moderately reduced when seeds were sampled every two or four years instead of yearly (from 59% to 48%). Together, our results suggest that seed survival is crucial to persistence of Helenium populations and that future empirical studies should focus on understanding the factors that affect seed survival. In addition, managers should consider seed bank censuses rather than above-ground plants when designing monitoring programs for plants in variable environments where above-ground plants vary greatly from year to year.     

A habitat-based population viability analysis for ocelots (Leopardus pardalis) in the United States

Strategies are needed to recover the ocelot Leopardus pardalis from the endangered species list. Recently, a population viability analysis (PVA) was developed which concluded that combinations of different recovery strategies were needed to effectively reduce ocelot extinction probability in the United States (US), with habitat protection and restoration identified as the most effective recovery scenario. We expanded this PVA model by incorporating landscape data to develop a more realistic habitat-based PVA for ocelots in southern Texas. We used RAMAS/gis software to conduct a habitat-based PVA by linking landscape data with a demographic metapopulation model. The primary goal of this study was to provide a model for evaluating ocelot recovery strategies in the US. Each model scenario was simulated 1000 times over 50 years and we defined extinction as one individual remaining. Using the RAMAS/gis program we identified 11 possible ocelot habitat patches (i.e., subpopulations) occurring in southern Texas. In addition, based on the habitat-based PVA model we found that combinations of different recovery strategies were needed to effectively reduce ocelot extinction probability in the US, with reducing road mortality the single most effective strategy. Short-term recovery strategies should include reducing ocelot road mortality, and translocation of ocelots into the US from northern Mexico. Long-term recovery strategies should include the restoration of habitat between and around existing ocelot habitat patches and the establishment of a dispersal corridor between ocelot breeding populations.     

Impact of grassland farming intensification on the breeding ecology of an indicator insectivorous passerine, the Whinchat Saxicola rubetra: Lessons for overall Alpine meadowland management

The decline of insectivorous farmland passerines has been attributed mostly to global decrease in arthropod availability, as a result of intensification of agricultural practices. The diminution of the Alpine Whinchat, once a widespread insectivorous passerine, has been ascribed to nest losses due to earlier and more frequent mowings. However, potential conjugated effects of deteriorated arthropod food availability had yet to be investigated. We compared food supply and nestling diet in intensively vs. traditionally managed grassland. Abundance and diversity of arthropods were much lower in intensive areas, where small-sized invertebrates, which do not enter nestling diet, were also predominant. Parents breeding in intensive habitats fed less biomass to nestlings than adults from traditional habitats. Nestling diet was less diverse and dominated by less profitable prey items in intensive than in traditional habitats. Feeding rate did not differ between the two habitats, but foraging distances from nest tended to be greater in intensive farmland. There were no significant differences in clutch sizes and hatching success with respect to management intensity, but fledging success was higher in traditional habitats. The recent intensification of farming practices has led to a decrease in the availability of grassland invertebrates, and of important Whinchat nestling food in particular, affecting parents’ foraging efficiency and reproductive success. Conservation actions must not only reduce nest losses by postponing mowing, but should also promote grassland farming that is less detrimental to invertebrates. Dominant at the study site, organic grassland farming does seemingly not provide sufficient conditions for Alpine Whinchats.     

临汾市西部山区封禁治理对策

对临汾市西部山区而言 ,封禁治理无论从经济方面还是从生态方面考虑都是科学合理的。该区应运用多种措施以增加生态系统的物能积累 ,即增加乔灌植被以加强系统的生态调节力 ,通过人口密度及产业种类调整以控制生态系统的物流损失并发展经济。针对划分的 4个封禁治理类型区 ,提出了具体的对策措施     

Population structure and movements of a threatened butterfly (Lopinga achine) in a fragmented landscape in Sweden

The red-listed butterfly Lopinga achine was studied by mark-recapture methods in southern Sweden for three seasons. We examined movement within and between populations and egg production in relation to age. The majority of the movements were small with mean movements between recaptures of 45-54 m for males and 94-116 m for females. There were few movements between sites, 20 of 996 recaptured males moved and 36 of 391 recaptured females, even though the distance to other sites was in many cases <100 m. The distance moved and the number of females moving between sites increased with increasing age. On average, a female that moves does so after laying two-thirds of its eggs in its natal site. It is therefore important to take account of the proportion of reproductive effort involved in dispersal when estimating colonisation ability. The males did not move more with increasing age. Female behaviour can be seen as a “spread-the-risk” strategy, an adaptation to the successional habitat of L. achine, whose natal site sooner or later will deteriorate. Butterflies like L. achine living in successional habitats may exhibit mobility that is intermediate between butterflies living in ephemeral habitats (very mobile) and in long-lived habitats (sedentary).     

严重侵蚀红壤封禁管理马尾松林水源涵养功能的恢复研究

对严重侵蚀红壤封禁管理马尾松林的水源涵养功能进行了研究 ,结果表明 :封禁管理后的马尾松林总持水量为 1717 872t/hm2 ,比对照的大 2 19 112t/hm2 ,其中地上部分持水量为 2 4 72 2t/hm2 ,是对照的 2 7 2倍 ,土壤 0～ 40cm土层最大持水量为 1693 15t/hm2 ,比对照的高 196 2 1t/hm2 ;表土层的初渗率和稳渗率均比对照的高。说明封禁管理治理模式马尾松林的水源涵养功能已有一定程度恢复     

The anatomy of a (potential) disaster: Volcanoes, behavior, and population viability of the short-tailed albatross (Phoebastria albatrus)

Catastrophic events, either from natural (e.g., hurricane) or human-induced (e.g., forest clear-cut) processes, are a well-known threat to wild populations. However, our lack of knowledge about population-level effects of catastrophic events has inhibited the careful examination of how catastrophes affect population growth and persistence. For the critically endangered short-tailed albatross (Phoebastria albatrus), episodic volcanic eruptions are considered a serious catastrophic threat since approximately 80% of the global population of ∼2500 birds (in 2006) currently breeds on an active volcano, Torishima Island. We evaluated how short-tailed albatross population persistence is affected by the catastrophic threat of a volcanic eruption relative to chronic threats. We also provide an example for overcoming the seemingly overwhelming problems created by modelling the population dynamics of a species with limited demographic data by incorporating uncertainty in our analysis. As such, we constructed a stochastic age-based matrix model that incorporated both catastrophic mortality due to volcanic eruptions and chronic mortality from several potential sources (e.g., contaminant exposure, fisheries bycatch) to determine the relative effects of these two types of threats on short-tailed albatross population growth and persistence. Modest increases (1%) in chronic (annual) mortality had a 2.5-fold greater effect on predicted short-tailed albatross stochastic population growth rate (lambda) than did the occurrence of periodic volcanic eruptions that follow historic eruption frequencies (annual probability of eruption 2.2%). Our work demonstrates that periodic catastrophic volcanic eruptions, despite their dramatic nature, are less likely to affect the population viability and recovery of short-tailed albatross than low-level chronic mortality.     

Population management of threatened taxa in captivity within their natural ranges: Lessons from Andean bears (Tremarctos ornatus) in Venezuela

Populations of threatened taxa in captivity within their natural ranges can make important contributions to conservation, but these may be compromised by the inappropriate application of population management goals developed in other contexts. We conducted demographic, genetic, and population viability analyses on the captive population of Andean bears (Tremarctos ornatus) in Venezuela to investigate the management of within-range captive populations in general, and to better integrate this population into the conservation of Andean bears in particular. We found that although the present population is very small and not internally self-sustaining, incorporation of confiscated wild individuals has resulted in a low average number of generations in captivity and low inbreeding, with moderate gene diversity and a high probability of future population persistence. However, past imports from extra-range populations have been from over-represented lineages of unknown origin, which have mixed with under-represented Venezuelan ones, reducing the future value of the Venezuelan population as a source for founder stock. Our analyses indicate that the rate of incorporation of wild recruits is a major factor influencing proxy measures of conservation value, and distinguishing within- from extra-range populations. This implies that, contrary to conventional wisdom, internal self-sustainability can be a misguided goal in within-range populations, which furthermore may not be suitable destinations for surplus animals from captive populations elsewhere.     

Scuba diver behaviour and the management of diving impacts on coral reefs

Coral reefs worldwide are attracting increasing numbers of scuba divers, leading to growing concern about damage. There is now a need to manage diver behaviour closely, especially as many dive companies offer unlimited, unsupervised day and night diving from shore. We observed 353 divers in St. Lucia and noted all their contacts with the reef during entire dives to quantify rates of damage and seek ways of reducing it. Divers using a camera caused significantly more contacts with the reef than did those without cameras (mean 0.4 versus 0.1 contacts min⁻¹), as did shore versus boat dives (mean 0.5 versus 0.2 contacts min⁻¹) and night versus day dives (mean 1.0 versus 0.4 contacts min⁻¹). We tested the effect of a one-sentence inclusion in a regular dive briefing given by local staff that asked divers to avoid touching the reef. We also examined the effect of dive leader intervention on rates of diver contact with the reef. Briefing alone had no effect on diver contact rates, or on the probability of a diver breaking living substrate. However, dive leader intervention when a diver was seen to touch the reef reduced mean contact rates from 0.3 to 0.1 contacts min⁻¹ for both shore and boat dives, and from 0.2 to 0.1 contacts min⁻¹ for boat dives. Given that briefings alone are insufficient to reduce diver damage, we suggest that divers need close supervision, and that dive leaders must manage diver behaviour in situ.