Commonness, population depletion and conservation biology

Species conservation practice, as opposed to principle, generally emphasizes species at risk of imminent extinction. This results in priority lists principally of those with small populations and/or geographical ranges. However, recent work emphasizes the importance of common species to ecosystems. Even relatively small proportional declines in their abundance can result in large absolute losses of individuals and biomass, occurrences significantly disrupting ecosystem structure, function and services. Here, we argue that combined with evidence of dramatic declines in once common species, this suggests the need to pay more attention to such depletions. Complementing the focus on extinction risk, we highlight important implications for conservation, including the need to identify, monitor and alleviate significant depletion events.     

Wattled Curassows in Bolivia: abundance,habitat use,and conservation status

ABSTRACT The Wattled Curassow (Crax globulosa) is a globally threatened species restricted to humid várzea forest (seasonally flooded forest along white‐water rivers) in low‐lying regions of Amazonia. The Wattled Curassow were thought to have been extirpated from the Beni area of Bolivia, but were rediscovered near the Río Negro River in 2001. Our objectives were to determine the size of this population, examine habitat use, and based on our results, assess the conservation status of the Wattled Curassow. During July and August 2006, we used distance sampling to estimate the population density in our study area. We estimated the density of Wattled Curassows at 3.4 (95% CI: 1.4–8.1) individuals/km² and all were observed within 300 m of the river. Based on the availability of suitable habitat (18 km² of riparian várzea habitat within 300 m of the river), we estimated that the breeding population of Wattled Curassows in our study area consisted of 61 individuals. The specialized habitat requirements of the Wattled Curassow has important conservation implications because previous population estimates were based on the availability of várzea forest rather than the availability of water edge habitat within várzea forest. As a result, the current global population estimate (2500–9999) is higher than our estimate (500–2500) that takes the specialized habitat requirements of the Wattled Curassow into account. Given this low estimated population, along with the severely fragmented state of the few remaining populations and their dependence on a specialized and vulnerable habitat, we recommend that the status of the Wattled Curassow be upgraded from Vulnerable to Endangered.     

On population abundance and niche structure

Recent published evidence indicates a negative correlation between density of populations and the distance of their environments to a suitably defined ‘niche centroid’. This empirical observation lacks theoretical grounds. We provide a theoretical underpinning for the empirical relationship between population density and position in niche space, and use this framework to understand the circumstances under which the relationship will fail. We propose a metapopulation model for the area of distribution, as a system of ordinary differential equations coupled with a dispersal kernel. We present an analytical approximation to the solution of the system as well as R code to solve the full model numerically. We use this tool to analyze various scenarios and assumptions. General and realistic demographic assumptions imply a good correlation between position in niche space and population abundance. Factors that modify this correlation are: transitory states, a heterogeneous spatial structure of suitability, and Allee effects. We also explain why the raw output of the niche modeling algorithm MaxEnt is not a good predictor of environmental suitability. Our results elucidate the empirical results for spatial patterns of population size in niche terms, and provide a theoretical basis for a structured theory of the niche.     

Integrating field sports,hare population management and conservation

Conflicts between field sports, animal welfare and species conservation are frequently contentious. In Ireland, the Irish Coursing Club (ICC) competitively tests the speed and agility of two greyhounds by using a live hare as a lure. Each coursing club is associated with a number of discrete localities, known as preserves, which are managed favourably for hares including predator control, prohibition of other forms of hunting such as shooting and poaching and the maintenance and enhancement of suitable hare habitat. We indirectly tested the efficacy of such management by comparing hare abundance within preserves to that in the wider countryside. In real terms, mean hare density was 18 times higher, and after controlling for variance in habitat remained 3 times higher, within ICC preserves than the wider countryside. Whilst we cannot rule out the role of habitat, our results suggest that hare numbers are maintained at high levels in ICC preserves either because clubs select areas of high hare density and subsequently have a negligible effect on numbers or that active population management positively increases hare abundance. The Irish hare Lepus timidus hibernicus Bell, 1837 is one of the highest priority species for conservation action in Ireland and without concessions for its role in conservation, any change in the legal status of hare coursing under animal welfare grounds, may necessitate an increase in Government subsidies for conservation on private land together with a strengthened capacity for legislation enforcement.     

Isozymes,plant population genetic structure and genetic conservation

Summary The exploration, conservation and use of the genetic resources of plants is a contemporary issue which requires a multidisciplinary approach. Here the role of population genetic data, particularly those derived from electrophoretic analysis of protein variation, is reviewed. Measures of the geographic structure of genetic variation are used to check on sampling theory. Current estimates justify the contention that alleles which have a highly localised distribution, yet are in high frequency in some neighbourhoods, represent a substantial fraction of the variation. This class, which is the most important class in the framing of sampling strategies, accounts for about 20–30% of variants found in 12 plant species. The importance of documenting possible coadapted complexes and gene-environment relationships is discussed. Furthermore, the genetic structure of natural populations of crop relatives might suggest the best structure to use in the breeding of crops for reduced vulnerability to pest and disease attack, or for adaptation to inferior environments. The studies reported to date show that whilst monomorphic natural populations do occur, particularly in inbreeding colonisers, or at the extreme margins of the distribution, polymorphism seems to be the more common mode. It is stressed here that the genetic resources of the wild relatives of crop plants should be systematically evaluated. These sources will supplement, and might even rival, the primitive land races in their effectiveness in breeding programmes. We may look forward to a wider application of gel electrophoresis in the evaluation of plant genetic resources because this technique is currently the best available for detecting genetic differences close to the DNA level on samples of reasonable size.     

Taxonomic complexity,population genetics,and plant conservation in Scotland

Summary

Groups of plants that are undergoing active diversification often do not fall into neat and tidy taxonomies. In such groups it can sometimes be very difficult to establish what does, and what does not, constitute a species. This presents problems for species-based conservation programmes that are based around prioritised species-lists (e.g. the UK Biodiversity Action Plans; BAPs), particularly as the inclusion or exclusion of taxa on these lists largely determines the allocation of conservation resources. This is an important issue as almost half of the BAP priority higher plant species for which Scotland has prime responsibility are taxonomically controversial.

Recent research using population genetic approaches to tackle some taxonomically complex plant groups has enhanced our understanding of their biology. Such approaches provide objective and independent assessments of whether a given entity is distinct or not. This information can then be used to contribute towards the decision making process of which taxa to prioritise for conservation, and address specific questions regarding BAP listed species. In the long term, however, a broader issue needs tackling. Actively evolving groups often contain a series of localised lineages, as well as complex populations that exhibit atypical levels of morphological diversity. These types of diversity do not fit well into a ‘standard’ species-based conservation system. In most cases protection will best be supplied by designated site protection or wider countryside habitat schemes. Where additional protection is need, a conservation policy is required that accepts the diversity in these actively evolving groups for what it is, rather than trying to squeeze it into conservation legislation derived for taxa whose delimitation is routine.     

Herbivory: effects on plant abundance, distribution and population growth

Plants are attacked by many different consumers. A critical question is how often, and under what conditions, common reductions in growth, fecundity or even survival that occur due to herbivory translate to meaningful impacts on abundance, distribution or dynamics of plant populations. Here, we review population-level studies of the effects of consumers on plant dynamics and evaluate: (i) whether particular consumers have predictably more or less influence on plant abundance, (ii) whether particular plant life-history types are predictably more vulnerable to herbivory at the population level, (iii) whether the strength of plant-consumer interactions shifts predictably across environmental gradients and (iv) the role of consumers in influencing plant distributional limits. Existing studies demonstrate numerous examples of consumers limiting local plant abundance and distribution. We found larger effects of consumers on grassland than woodland forbs, stronger effects of herbivory in areas with high versus low disturbance, but no systematic or unambiguous differences in the impact of consumers based on plant life-history or herbivore feeding mode. However, our ability to evaluate these and other patterns is limited by the small (but growing) number of studies in this area. As an impetus for further study, we review strengths and challenges of population-level studies, such as interpreting net impacts of consumers in the presence of density dependence and seed bank dynamics.     

Range contraction and conservation of the endangered Yellow Cardinal

The Yellow Cardinal (Gubernatrix cristata) is distributed in Argentina, Uruguay and Brazil, inhabiting environments of xerophytic woodland and savannah; it is considered globally Endangered since 1994. Populations are under pressure from loss and modification of habitat and from capturing for the cage bird trade. We compared in a geographical analysis the past (1826–1994) and recent (1995–2018) distributional ranges of the Yellow Cardinal and its affinities to ecoregions, land use cover and presence in protected areas, and assessed continuity vs. fragmentation of the current distribution using the method of Medium Propinquity. We used 1191 location records from reviewed sources and our field observations. We found a reduction of the original distribution to areas where native savannahs are still in good condition. In Argentina, the species has disappeared from 8 out of 16 provinces. The altitudinal range of the species extends up to 1100 m, rather than 700 m as reported in earlier reviews. It is clearly associated with savannah, shrubland, and grassland land cover categories. In regions where it disappeared, suitable habitat remained at 33% of points where it was formerly present, with capturing for the cage bird trade as a likely cause of disappearance. Medium propinquity analysis showed as yet little fragmentation in the current distribution, except for a separation between northern and southern populations. The Yellow Cardinal is distributed mainly outside protected areas; it is found in 31 Important Bird Areas, 22 of which are not protected and are under threat from habitat loss through the expansion of agriculture. We urge improved control of illegal capturing and the maintaining of native vegetation in population strongholds of the Yellow Cardinal.     

Distribution, abundance, and conservation of Vinaceous Amazons (Amazona vinacea) in Argentina and Paraguay

ABSTRACT.   Vinaceous Amazons ( Amazona vinacea ) are endemic to the Atlantic forest of southeastern Brazil, eastern Paraguay, and the province of Misiones in Argentina. We searched for Vinaceous Amazons throughout the western part of its range in Argentina and Paraguay during 1639 days of fieldwork from 1997 to 2006. These parrots have disappeared from most areas where they were historically recorded in these countries, and are now limited to a few sites in northeastern Paraguay and central Misiones (Argentina). We estimate the minimum remaining populations at 220 individuals in Paraguay and 203 individuals in Argentina. Important sites for the species are (1) the farming area from San Pedro to Tobuna (Misiones, Argentina) and (2) the Itaipú reserves complex and Reserva Natural Privada Itabó (Paraguay). In our surveys, Vinaceous Amazons were absent from the largest tracts of forest in Misiones, and were most often observed feeding, roosting, and nesting in small forest remnants and in agricultural areas that included forest fragments and isolated trees. Threats to amazons in these areas include nest poaching, forest clearing, and being shot as a crop pest. We confirmed 40 Vinaceous Amazons kept as pets in 35 homes between San Pedro and Tobuna. Environmental education and law enforcement are urgently needed to reduce threats in populated areas, and subsistence farmers need technical and logistical support to slow or stop the conversion of forest into cropland. Finally, additional study is needed to determine this amazon's habitat preferences, nest site requirements, and demography in different habitats.     

Range limits and geographic patterns of abundance of the rocky intertidal owl limpet,Lottia gigantea

Aim We evaluate the stability of the range limits of the rocky intertidal limpet, Lottia gigantea, over the last c. 140 years, test the validity of the abundant centre hypothesis, and test indirectly the roles played by recruitment limitation and habitat availability in controlling the range limits. Because this species is size‐selectively harvested, our results also allow us to assess conservation implications. Location The Pacific coast of North America, from northern California to southern Baja California (41.74° N–23.37° N), encompassing the entire range of L. gigantea. Methods The historical and modern distributions of L. gigantea were established using museum data and field observations. Overall and juvenile abundances of local populations were estimated at 25 field sites. The spatial distribution of abundance was evaluated statistically against the predictions of five hypothetical models. The availability of habitat was estimated by measuring the percentage of unavailable sandy beach within cumulative bins of coast across the range of L. gigantea. Results The northern limit of L. gigantea has contracted by c. 2.4° of latitude over recent decades (after 1963), while the southern limit has remained stable. The highest abundances of L. gigantea occur in the centre of its geographic range. Habitat availability is ample in the centre and northern portions of its range, but is generally lacking in the southern range. The northern range is only sparsely populated by adults, with sharp declines occurring north of Monterey Bay (36.80° N). In the southern range, abundance drops precipitously south of Punta Eugenia (27.82° N), coinciding with the region where suitable habitat becomes sparse. Main conclusions Support for the abundant centre hypothesis was found for L. gigantea. Northern populations are characterized as being recruitment‐limited, demographically unstable and prone to local extinctions, while southern populations are suggested to be habitat‐limited. The abundant centre is suggested to result partly from a combination of the indirect effects of human harvesting, generating denser populations of smaller individuals, and larval recruitment from well‐protected offshore rocky islands primarily found in the range centre.     

Relationship between resource selection, distribution, and abundance: a test with implications to theory and conservation

Much of applied and theoretical ecology is concerned with the interactions of habitat quality, animal distribution, and population abundance. We tested a technique that uses resource selection functions (RSF) to scale animal density to the relative probability of selecting a patch of habitat. Following an accurate survey of a reference block, the habitat-based density estimator can be used to predict population abundance for other areas with no or unreliable survey data. We parameterized and tested the technique using multiple years of radiotelemetry locations and survey data collected for woodland caribou across four landscape-level survey blocks. The habitat-based density estimator performed poorly. Predictions were no better than those of a simple area estimator and in some cases deviated from the observed by a factor of 10. We developed a simulation model to investigate factors that might influence prediction success. We experimentally manipulated population density, caribou distribution, ability of animals to track carrying capacity, and precision of the estimation equation. Our simulations suggested that interactions between population density, the size of the reference block, and the pattern of distribution can lead to large discrepancies between observed and predicted population numbers. Over- or undermatching patch carrying capacity and precision of the estimator can influence predictions, but the effect is much less extreme. Although there is some empirical and theoretical evidence to support a relationship between animal abundance and resource selection, our study suggests that a number of factors can seriously confound these relationships. Habitat-based density estimators might be effective where a stable, isolated population at equilibrium is used to generate predictions for areas with similar population parameters and ecological conditions.     

Patterns of Orthoptera abundance and lesser kestrel conservation in arable landscapes

The lesser kestrel Falco naumanni experienced a marked decline during the second half of the 20th century due to changes in land use that influenced breeding success by reducing the abundance and quality of prey. However, the factors governing spatial and temporal variation of prey abundance around lesser kestrel colonies has not yet been investigated. We sampled Orthoptera abundance in the main crop types and edge habitats surrounding six lesser kestrel colonies in southern Spain. Samplings focused on Orthoptera because they constitute the main prey during the nestling period. Only those Orthoptera species that are known to be preyed by lesser kestrels were considered in this study. We found differences in prey density among localities, and crop types. Semi-natural habitats such as grasslands, fallow land, and field margins held the highest densities. However, prey abundance showed a complex pattern that was not possible to explain solely on the basis of crop composition around colonies. Factors determining productivity in individual fields like soil type and productivity or biocide input, and mean size of agricultural fields contributed to explain this complex pattern of prey abundance. Our results highlight the key role of semi-natural and edge habitats in farmed landscapes as prey reservoirs and corridors. Higher conservation priorities for these habitats are suggested to benefit foraging lesser kestrels, but many other farmland species that also experienced steep population declines due to decreasing food supply resulting from modern agriculture.     

Body size varies with abundance,not climate,in an amphibian population

Body size variation among animals has many possible correlates, temporal as well as geographic. Adult male body size was analysed over the course of 23 yr (1989–2011) in a population of Fowler’s toads Anaxyrus fowleri at Long Point, Ontario. We used an information theoretic approach to identify the most likely models to explain body length variation in relation to abundance, age and environmental variables, including temperature. Male toads overall averaged 53.6 ± 0.1 (SE) mm (n = 1976) but average body length from year to year varied from 50.9 ± 0.2 to 61.4 ± 1.3 mm (n = 23 yr), a difference of 18.7%. Abundance was the only variable significantly correlated with body size variation (R²= 0.713, p = < 0.001). A significant 10‐yr trend in increased body size (R²= 0.874, p = < 0.001) was coincident with a previously detected negative trend in abundance. A 0.05°C yr^?1 increase in environmental temperature over the course of our study was not significantly correlated with the toads’ body size. Body size variation in these toads is likely related to density‐dependent resource availability for growth in the terrestrial stage. Temporal changes in average body size within populations in relation to density may be a significant component of phenotypic variation.     

Resilience,vulnerability and conservation strategies in high-mountain pine forests in the Gredos Range,central Spain

Background: High-mountain pine forests and broom communities in central Spain today have led to contrasting interpretations of their natural or human-induced origin.

Aims: We evaluated the vulnerability and resilience of high-mountain Pinus sylvestris/P. nigra forests and derived Cytisus broom scrub communities to climate and anthropogenic disturbances.

Methods: We assessed historical transitions from forest to scrub and their relation to climate and human influences, using a multi-proxy paleoenvironmental study (pollen, non-pollen palynomorphs, charcoal, magnetic susceptibility) in three mires in the Gredos Range, western Iberian Central System.

Results: High percentages of Pinus sylvestris/nigra pollen and the identification of their macro remains demonstrated that high-mountain pine forests have been present in the oromediterranean bioclimatic belt of the Gredos Range since the mid-Holocene. After that, a major human-induced decline, enhanced by climate conditions, has led to their gradual replacement by broom communities.

Conclusions: Broom communities are derived from ancient pine forests that were intensively transformed by human activities after 700 cal year BP, and largely disappeared by ca. 500 cal yr BP. Today’s landscape, dominated by broom scrub and grasslands with scattered stands of pines, shows high resilience and provides suitable refugia for a rich mountain biodiversity which deserves a further protection.     

The consequences of polyandry for population viability,extinction risk and conservation

Polyandry, by elevating sexual conflict and selecting for reduced male care relative to monandry, may exacerbate the cost of sex and thereby seriously impact population fitness. On the other hand, polyandry has a number of possible population-level benefits over monandry, such as increased sexual selection leading to faster adaptation and a reduced mutation load. Here, we review existing information on how female fitness evolves under polyandry and how this influences population dynamics. In balance, it is far from clear whether polyandry has a net positive or negative effect on female fitness, but we also stress that its effects on individuals may not have visible demographic consequences. In populations that produce many more offspring than can possibly survive and breed, offspring gained or lost as a result of polyandry may not affect population size. Such ecological ‘masking’ of changes in population fitness could hide a response that only manifests under adverse environmental conditions (e.g. anthropogenic change). Surprisingly few studies have attempted to link mating system variation to population dynamics, and in general we urge researchers to consider the ecological consequences of evolutionary processes.