Population Trends Of Species Research Articles

Population trends of wintering waterbirds in Lombardy between 2002 and 2013

Birds are among the most important biological components of wetlands. They play a key role in their ecology and are an important cultural resource for the public, in part because some species can be legally hunted. The conservation of waterbirds is especially important in terms of land use planning, in light of their ecological, cultural, and economic value. Here we summarize the results of wintering waterbirds censuses carried out in Lombardy between 2002 and 2013, using the standardized International Waterbird Census methodology. Our goals were to identify priority sites for waterbirds; estimate population sizes; define demographic trends; and provide a technical framework for making administrative and legislative decisions on the management and conservation of wetlands and their bird species. Lombardy hosts substantial numbers of wintering waterbirds, and many of its wetlands qualify as areas of conservation interest under Ramsar Convention criteria, as they host >1% of the Italian population of one or more species. Trends for the 20 species of highest conservation or hunting interest showed stable or increasing populations in most cases, with the exception of Black-necked Grebe, Common Pochard, and Eurasian Coot, which instead decreased in 2002-2013. The favourable population trends for most species suggest that the ecological status of Lombardy’s wetlands is essentially stable, but it could be improved by simple measures to improve the natural value of the shorelines and bottoms of major lakes and flooded gravel pits. Hunting was one of the main factors affecting the distribution and abundance of wintering waterbirds, which concentrate in protected areas - over 50% of all birds, rising to over 70% for species of conservation interest concentrate there, despite the fact that protected areas only account for 43% of sites surveyed. Overall, protected areas hosted bird densities that were almost seven times higher than those managed primarily for hunting, while mixed-use areas hosted intermediate densities of birds. The presence of protected and unprotected areas within the same wetland mitigates the effects of hunting on bird populations and species diversity, and may help maintain adequate conditions for their conservation.

EDITOR'S CHOICE: Safeguarding Sumatran tigers: evaluating effectiveness of law enforcement patrols and local informant networks

Summary The United Nations recently listed illegal wildlife trade as a serious crime because of the escalating demand for highly prized species, such as tiger and rhinoceros, and the failure to effectively control the trade. In turn, this places greater urgency on reducing supply by securing source populations of these species. Yet, whether law enforcement strategies designed to mitigate poaching are succeeding remains poorly understood, despite the millions of dollars invested annually in this mainstay conservation strategy. Here, we assess the performance of one of Asia's longest running law enforcement programmes, from Kerinci Seblat National Park in Sumatra, by investigating whether forest ranger patrols reduced the occurrence of snare traps set for tiger and its ungulate prey base; local informant reports on poaching influenced ranger patrol success; and the resulting population trends of target species changed in response to these conservation actions. A total of 4433 snare traps were removed during 642 foot patrols conducted from 2000 to 2010. Controlling for the influence of varying detection probabilities, as well as accessibility and other possible determinants of illegal hunting, revealed that sites with a greater frequency of patrols, rather than the combined distance walked, had a lower occurrence of snare traps in succeeding years. Patrols conducted on the basis of local informant ‘tip‐offs’ were significantly more likely to detect snare traps than routine patrols, with reports increasing detections by over 40%. There were no significant changes in the occupancy status of the tiger prey base from 2004 to 2011, suggesting that it remained stable during this period. The relatively good condition of prey and predator populations in Kerinci Seblat National Park was further supported by the results of an independent survey conducted in 2008–2009 which revealed a widespread tiger occurrence. Synthesis and applications. Our results not only demonstrate the effectiveness of the Kerinci Seblat law enforcement strategy in protecting wildlife, but highlight the benefits from cultivating a network of reliable informants. The study also represents a critical step in helping these urgently needed conservation assessments to become common place in the fight to save flagship species.

Evaluating the Potential of Aerial Infrared as a Lek Count Method for Prairie Grouse

Abstract Wildlife biologists use counts of birds attending traditional breeding grounds (i.e., leks) to develop indices of population trends in several grouse species. Standardized lek counts for sage-grouse Centrocercus spp. provide information about population trends by allowing comparison of counts across their range. In contrast, biologists lack a standard lek-count method for prairie grouse Tympanuchus spp.. The lack of a standard lek-count method limits our ability to make rigorous spatial and temporal comparisons or to estimate population trends. Recent use of cooled infrared cameras in aerial surveys and their increased affordability make this technology attractive for monitoring prairie grouse populations. Our objective was to evaluate the efficacy of aerial infrared (AIR) technology for estimating abundance of prairie grouse by comparing AIR lek counts with ground-based lek counts of Columbian sharp-tailed grouse T. phasianellus columbianus in Idaho. We used both methods simultaneously to count sharp-tailed grouse at 25 leks to compare method consistency. We also used both methods to count sharp-tailed grouse at 88 other leks to quantify and compare the resources required for both methods. The average count obtained with the AIR method (12.3 grouse ± 1.5 SE) and the ground-based method (12.9 grouse ± 1.8 SE) was similar, and we were unable to detect a statistical difference between methods when conducting a negative binomial regression (z = 0.165, P = 0.87). Aerial infrared was twice the cost of the ground-based method, but AIR surveyed more leks in less time (88 leks during 4 d) compared with the ground-based method (88 leks during 29 d). Aerial infrared improves population monitoring by counting leks inaccessible by ground. The time efficiency of AIR and the ability to obtain counts consistent with ground-based methods suggests that AIR may be an effective and efficient lek-count method.

Global large carnivore conservation and international law

International cooperation, including through international legal instruments, appears important for the conservation of large carnivores worldwide. This is due to, inter alia, the worrying conservation status and population trends of many large carnivore species; the importance of large carnivores for biodiversity conservation at large; their occurrence at low densities, with many populations extending across various countries; and the international nature of particular threats. For the 31 heaviest species in the order Carnivora, this study (i) documents to what extent existing international legal instruments contribute to large carnivore conservation, and (ii) identifies ways of optimizing their contribution in this regard. From this dual perspective, it reviews all global wildlife conservation treaties—Ramsar Wetlands Convention, World Heritage Convention, Convention on Trade in Endangered Species, Convention on Migratory Species (CMS), Convention on Biological Diversity (CBD)—and selected regional instruments, using standard international law research methodology. Results indicate that a substantial body of relevant international law already exists, whereas simultaneously there is clear potential for enhancing the contribution of international law to large carnivore conservation. Avenues for pursuing this include promotion of instruments’ effective implementation; clarification of their precise implications for large carnivore conservation; development of formal guidance; expansion of instruments’ scope in terms of species, sites and countries; and creation of new instruments. The CMS and CBD hold particular potential in some of these respects. The experiences being gained under European legal instruments constitute an interesting ‘laboratory’ regarding human coexistence with expanding large carnivore populations and transboundary cooperation at the (sub)population level.

Using automated recorders and occupancy models to monitor common forest birds across a large geographic region

ABSTRACTAutomated recorders and occupancy models can be used together to monitor population trends of multiple avian species across a large geographic region. Automated recorders are an attractive method for monitoring birds, because they leave a record that can be independently validated and multiple units can be programmed to repeatedly survey different locations at the same daily times. We assessed the use of automated recorders and single‐species, single‐season occupancy models to monitor common forest birds across a 5.4‐million‐ha region of northern California. Using a survey protocol of 5‐minute recordings at 3 times of the morning repeated over 3 consecutive days at 453 sites, we detected 32 species at >10% of these sites. Five of these species (Steller's jay [Cyanocitta stelleri], mountain chickadee [Poecile gambeli], red‐breasted nuthatch [Sitta canadensis], dark‐eyed junco [Junco hyemalis], and western tanager [Piranga ludoviciana]) were dominant with occupancies >0.5. We also modeled occupancy associations with elevation and canopy cover for brown creeper (Certhia americana), MacGillivray's warbler (Geothlypis tolmiei), and western tanager and found the environmental conditions at which occupancy was maximized differed by up to 399 m in elevation and 17.9% canopy cover for these species. Given a sampling effort of 100 new sites per year, we demonstrated 80% power (α = 0.1) to detect occupancy declines as small as 2.5% per year over 20 years for the 32 most common species. The effective radius of automated recorder surveys was approximately 50 m. In a field test, surveys conducted concurrently using automated recorders and point counts yielded similar occupancy estimates despite differences in detection probability. Our results suggest that automated recorders, used alone or in conjunction with point counts, can provide a practical means of monitoring common forest birds across a large geographic area. © 2014 The Wildlife Society.

Mapping perceptions of species' threats and population trends to inform conservation efforts: the Bornean orangutan case study

AbstractAimWe demonstrate a robust approach for predicting and mapping threats and population trends of wildlife species, invaluable for understanding where to target conservation resources. We used the endangered Bornean orangutan (Pongo pygmaeus) as our case study to facilitate and strengthen conservation efforts by the Indonesian government to stabilize populations by 2017.LocationKalimantan, Indonesian Borneo.MethodsLocal knowledge of threats to orangutan populations was gathered through questionnaire interviews in 531 villages (512 in Kalimantan) within known orangutan range. These data were integrated with 39 environmental/socio‐economic spatial variables using boosted regression tree modelling to predict threat levels and population trends across Kalimantan and to identify key combinations of threats and trends that can help to direct appropriate conservation actions.ResultsNineteen percentage of villages surveyed in Kalimantan reported human–orangutan conflicts. High‐predicted conflict likelihood was extensive, strongly associated with road density (very low or high) and temperature seasonality. Recent orangutan killings were reported in 23% of villages. High killing risk was highly associated with greater surrounding orangutan habitat and for villages more than 60 km from oil palm plantations. Killings by respondents were reported in 20% of villages with higher likelihoods associated with greater range in rainfall and temperature, and higher proportion of Christian believers. Orangutan populations were predicted to decline/become locally extinct across the majority of their range in Kalimantan over the next decade, with few regions predicted to support stable populations.Main conclusionsHuman–orangutan conflicts and killings occur extensively in Kalimantan, with many populations at risk of decline or localized extinctions. Effective conservation actions are therefore urgently needed. Our approach better informs conservation managers in understanding the extent, spatial patterns and drivers of threats to endangered species such as the orangutan. This is essential to better design management strategies that can minimize or avert the species' decline.

Distribution and population trends of waterbird species wintering in Basque estuaries (North of Spain): a 22-year study

Distribution and population trends of waterbird species wintering in Basque estuaries (North of Spain): a 22-year study

Ecological and life‐history traits explain recent boundary shifts in elevation and latitude of western North American songbirds

AbstractAimSpecies are expected to move uphill or poleward in response to climate change, yet their distributions show idiosyncratic responses; many species are moving in the predicted direction, but others are not shifting at all or are shifting downhill or towards the equator. Fundamental questions remain about the causes of interspecific variation in range responses and whether shifts along elevational and latitudinal gradients are correlated. We examined whether shifts in northern‐latitude and upper‐elevation boundaries of western North American songbirds over a 35‐year period were correlated and whether species ecological and life‐history traits explained interspecific variation in observed shifts.LocationNorth America.MethodsWe used data from the North American Breeding Bird Survey to determine shifts in northern‐latitude and upper‐elevation boundaries of 40 North American songbird species between two time periods, 1977–81 and 2006–11. We used an analysis of covariance approach that controlled for species population trends and changes in survey effort to test whether: (1) songbirds shifted in elevation, latitude or both; (2) shifts in elevation and latitude were correlated; and (3) responses could be explained by species‐level traits including life history, ecological generalization and dispersal capability.ResultsThe majority of species shifted uphill and poleward during this period, but there was no correlation between the distances that species range boundaries shifted in elevation and latitude. Species with smaller clutch sizes and narrower diet breadths exhibited greater northward shifts, while species with larger clutch sizes and narrower diet breadths exhibited greater uphill shifts.Main conclusionsShifts in latitude and elevation were not correlated. However, a common set of species‐level traits explained differential responses among species to climate change. Consideration of shifts in both elevation and latitude is needed to understand the full extent to which species are tracking changing climates.

Birds protected by national legislation show improved population trends in Eastern Europe

Protecting species is one of the major focuses of conservation efforts. However, large-scale assessments of the effects of species protection on animal populations are rare. Protection has been shown to benefit birds in Western Europe and in the United States, but not yet in Eastern Europe, where modern environmental legislation was only established in the early 1990s after political changes. We compared the population trends of bird species between 1970–1990 and 1990–2000 in ten Eastern European countries for species protected since 1990s and unprotected species, controlling for effects of species’ phylogeny and traits. After 1990, trends in protected species improved more than in unprotected species. This suggests that national legislation has helped prevent declines of the protected species, although there was a high variability in population trends among countries. In particular, there was great improvement in the population trends of protected species in countries providing ‘narrow and deep’ protection to few species. In contrast, trends of protected species remained nearly unchanged in countries providing ‘broad and shallow’ protection to most species, while few unprotected species had adverse population trends in these countries. Although our correlative analysis cannot show causal relationships, the positive relationship between protection and long-term population trends suggests that species protection is a highly relevant tool for conservation. A combination of ‘broad and shallow’ and ‘narrow and deep’ protection might be most efficient for securing healthy bird populations for the future.

Monitoring Strategy for Eight Amphibian Species in French Guiana, South America

Although dramatic amphibian declines have been documented worldwide, only few of such events have been quantitatively documented for the tropical forests of South America. This is due partly to the fact that tropical amphibians are patchily distributed and difficult to detect. We tested three methods often used to monitor population trends in amphibian species in a remote lowland tropical forest of French Guiana. These methods are capture-mark-recapture (CMR), estimation of the number of calling males with repeated counts data and distance sampling, and rates of occupancy inferred by presence/absence data. We monitored eight diurnal, terrestrial amphibian species including five Dendrobatidae and three Bufonidae. We found that CMR, the most precise way of estimating population size, can be used only with two species in high density patches where the recapture rate is high enough. Only for one of the species (Dendrobates tinctorius), a low coefficient of variation (CV = 0.19) can be achieved with 15 to 20 capture events. For dendrobatid species with day-calling males, audio surveys yield a better probability of detection with only 8 audio surveys needed; quantitative estimates can be achieved by computing the number of calling males inferred from audio counts or distance sampling analysis. We therefore suggest that an efficient monitoring protocol for Neotropical amphibian species should include a combination of sighting and audio techniques, and we discuss the need of implementing a large-scale monitoring in order to provide a baseline for comparison with future changes.

Inference for finite-sample trajectories in dynamic multi-state site-occupancy models using hidden Markov model smoothing

Ecologists and wildlife biologists increasingly use latent variable models to study patterns of species occurrence when detection is imperfect. These models have recently been generalized to accommodate both a more expansive description of state than simple presence or absence, and Markovian dynamics in the latent state over successive sampling seasons. In this paper, we write these multi-season, multi-state models as hidden Markov models to find both maximum likelihood estimates of model parameters and finite-sample estimators of the trajectory of the latent state over time. These estimators are especially useful for characterizing population trends in species of conservation concern. We also develop parametric bootstrap procedures that allow formal inference about latent trend. We examine model behavior through simulation, and we apply the model to data from the North American Amphibian Monitoring Program.

Managing Conservation Reliant Species: Hawai'i's Endangered Endemic Waterbirds

Hawai'I's coastal plain wetlands are inhabited by five endangered endemic waterbird species. These include the Hawaiian Coot ('alae ke'oke'o), Hawaiian Duck (koloa maoli), Hawaiian Stilt (ae'o), Hawaiian Gallinule (Moorhen) ('alae 'ula), and Hawaiian Goose (nēnē). All five species are categorized as being “conservation reliant.” The current strategy to recover these endangered birds includes land protection and active management of wetlands. To assess the effectiveness of the current management paradigm, we compared species population trends across the state to those on six actively managed wetland national wildlife refuges (Refuges) thought to be critical for the survival of these endangered species. To perform the evaluation we relied on systematic semiannual population counts that have been conducted across most wetlands in the state and monthly population counts that have occurred on Refuges during the same time period. We found that statewide and Refuge populations of the Hawaiian Coot, Stilt and Gallinule have rebounded from historic lows and over the last 20 years have slowly increased or remained stable. We also documented that Refuges are important to each species year-round and that a disproportionately larger percentage of the population for each species is found on them. Understanding of why Refuges successfully house a disproportionate percentage of these “conservation reliant” species can inform current and future conservation efforts as well as ensure long-term population viability for these species.

Bridging the gap between ecosystem modeling tools and geographic information systems: Driving a food web model with external spatial–temporal data

Research toward the impacts of climate change and human activities on marine ecosystems is challenged by the limitations of present-day ecosystem models to address the interrelated spatial dynamics between climate, ocean chemistry, marine food webs, and human systems. The work presented here, the spatial–temporal data framework, is part of a larger study, the NF-UBC Nereus Program, to develop a new approach to model interoperability for closing the gap between marine ecosystem modeling tools via geographic information systems (GIS) technology. The approach we present simplifies interdisciplinary model interoperability by separating technical and scientific challenges into a flexible and modular software approach. To illustrate capabilities of the new framework, we use a remote-sensing derived spatial and temporal time series to drive the primary production dynamics in an existing food web model of the North-Central Adriatic using the Ecospace module of the Ecopath with Ecosim approach. In general, the predictive capabilities of the food web model to hind-cast ecosystem dynamics are enhanced when applying the new framework by better reflecting observed species population trends and distributions. Results show that changes at the phytoplankton level due to changes in primary production are realistically reproduced and cascade up the pelagic food web. The dynamics of zooplankton and small and large pelagic fish are impacted. Highly exploited demersal species such as European hake do, however, not show clear signs of cascading. This may be due to the high fishing pressure on this species and the resulting strong historical decline in the area. In general, the development of the new framework offers ecosystem modelers with unprecedented capabilities to include spatial–temporal time series into food web analysis with a minimal set of required steps. It is a promising step toward integrating species distribution models and food web dynamics, and future implementations of interdisciplinary model interoperability.

Survival of rockhopper penguins in times of global climate change

ABSTRACT Anthropogenic changes in the marine environment and global climate change have led to population declines in several seabird species worldwide. Rockhopper penguins (Eudyptes chrysocome and Eudyptes moseleyi) have experienced a dramatic population decline, potentially linked to increasing sea surface temperatures (SST). Among Southern Ocean diving seabirds, rockhopper penguins typically occupy a low trophic level, and might therefore be expected to mirror climate‐driven bottom‐up changes to the food web sensitively and on a short time scale. Using passive integrated transponders, survival rates of adults in a colony of southern rockhopper penguins (E. chrysocome) on the Falkland Islands were monitored over five consecutive years. Mean annual survival rates were in the range 84 to 96%. These values are high compared with other crested penguin species and reflect the generally good conditions during the study period, when low SST prevailed. However, survival rates were lower in 2010, corresponding to very cold conditions. Curve fits showed a best‐fit quadratic relationship between average SST anomaly and survival rates for the present data, as well as for a data set including two additional years from a different study at Staten Island. Results of this study suggest that rockhopper penguins survive best at SSTs that are lower than the average of the last four decades. In accordance with previously observed rockhopper penguin population declines, the present data suggest that rockhopper penguins are highly sensitive to changes in SST and their effects on the food web, a worrying perspective in times of global climate change. It seems likely that these changes could, in the long term, also affect population trends of other seabird species with similar ecological preferences. The most promising conservation approach should aim at enhancing ecosystem resilience, mainly by reducing industrial fishing and oil exploitation. This would allow the currently over‐exploited fish and squid stocks to recover, offering larger food resources to seabirds and other vertebrate species. Copyright © 2013 John Wiley & Sons, Ltd.

Europe Needs a New Vision for a Natura 2020 Network

AbstractTwenty years after the world's nations agreed upon the Convention on Biodiversity, there is still a global decline in biodiversity. At present it seems unlikely that the Aichi Targets of halting biodiversity loss by 2020 will be met. Although the European Union is often seen as a pioneer in this regard, as its “Habitats Directive” represents one of the strongest legal tools in nature conservation, biodiversity continues to decline even in Europe. We outline four major problems in the current implementation of the directive. First, prioritization needs to be based upon comprehensive scientific knowledge. This requires a maximized number of red list assessments of European species and a regular adaptation of the annexes in order to focus on those sites with the highest conservation value. Second, strategic conservation plans need to be compiled for highly threatened species and adaptive management plans need to be implemented in each reserve. Third, an improved “on‐ground” monitoring system is necessary, focusing on population trends of priority species and feeding back to management plans and red list assessments. Fourth, substantial financial resources have to be invested in the implementation as well as education in order to reach a societal consensus on the necessity for conservation.

Are species' responses to global change predicted by past niche evolution?

Predicting how and when adaptive evolution might rescue species from global change, and integrating this process into tools of biodiversity forecasting, has now become an urgent task. Here, we explored whether recent population trends of species can be explained by their past rate of niche evolution, which can be inferred from increasingly available phylogenetic and niche data. We examined the assemblage of 409 European bird species for which estimates of demographic trends between 1970 and 2000 are available, along with a species-level phylogeny and data on climatic, habitat and trophic niches. We found that species' proneness to demographic decline is associated with slow evolution of the habitat niche in the past, in addition to certain current-day life-history and ecological traits. A similar result was found at a higher taxonomic level, where families prone to decline have had a history of slower evolution of climatic and habitat niches. Our results support the view that niche conservatism can prevent some species from coping with environmental change. Thus, linking patterns of past niche evolution and contemporary species dynamics for large species samples may provide insights into how niche evolution may rescue certain lineages in the face of global change.

Impact of an invasive alga (Womersleyella setacea) on sponge assemblages: compromising the viability of future populations

The effects of invasive species on native fauna are understudied, even though their consequences should be taken into consideration for the proper conservation and management of marine systems. Furthermore, bioinvasions may have greater consequences if they affect key structural species with slow dynamics such as marine sponges. We propose that reproductive output could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species (i.e. sponges) as a result of biological invasions. The aim of this study was to investigate the effects of invasive algal (Womersleyella setacea) overgrowth on sponge reproduction by comparing the presence of reproductive elements (spermatic cysts, oocytes, embryos, and larvae) in sponges covered by a thick carpet of the invasive algae and in sponges dwelling in the same habitat but without the invasive algae. Three variables were calculated to assess the impact of the invasive alga on sponge reproduction: the reproductive effort, the proportion of individuals in reproduction, and the size of the reproductive structures. We studied eight sponge species representing the main components of the deep rocky reefs of the area. Our results showed that W. setacea had a strong negative effect on sponge reproduction in six out of eight sponge species studied, with lower and even nil reproductive structures on the sponges subjected to the algal overgrowth. Thus, considering that sexual reproduction is necessary for the persistence of most sponge populations, a significant and constant reduction of the reproductive effort may compromise their viability and affect future trends in these benthic systems.

Climate change, phenology and species detectability in a monitoring scheme

AbstractThe knowledge of the state of biodiversity on the globe is based on a large number of monitoring schemes. Quite often the results of these schemes are sensitive to the timing of monitoring due to the phenology of species, which in turn may affect the detectability of species during censuses. As global warming has been shown to cause changes in phenology, there is an increasing risk that species detectability will be altered if the timing of monitoring is not adapted to this change. I tested how sensitive species detectability is to the timing of censuses and whether there are potential climate‐driven temporal changes in the detectability of 73 Finnish land bird species monitored using single‐visit line‐transects in 1987–2010. This was done by investigating seasonal and annual patterns in the proportion of birds in the main belt and those detected by displaying activity. Over 20 of the study species showed significant changes in detectability within the census season. However, only three species showed a significant trend in annual detectability. According to multi‐species analyses there was a slight but significant increasing trend in the proportion of displaying birds and a slight decreasing trend in the proportion of birds in the main belt. However, the observed species‐specific annual changes in displaying activity or in proportion of birds in main belt were not associated with the observed population trends of species during the same period. Nevertheless, the findings highlight a strong potential risk that species detectability can change if climate change escalates in the future. I recommend researchers to investigate how sensitive their monitoring systems are for phenological changes and prepare tools for taking potential changes in detectability into account.

Response of palila and other subalpine Hawaiian forest bird species to prolonged drought and habitat degradation by feral ungulates

Extinction has claimed half of all historically-known Hawaiian passerines, and today many extant species are increasingly threatened due to the combined effects of invasive species and climate change. Habitat disturbance has affected populations of feeding specialists most profoundly, and our results indicate that specialists continue to be most vulnerable, although even some abundant, introduced, generalist species also may be affected. Surveys of passerines during 1998–2011 in subalpine woodland habitat on Mauna Kea Volcano, Island of Hawai′i, revealed that the abundance of the critically endangered palila (Loxioides bailleui), a seed specialist, declined by 79% after 2003. The ′akiapōlā′au (Hemignathus munroi), an endangered specialist insectivore, was not detected in the survey area after 1998. The Hawai′i ′amakihi (Hemignathus virens virens), a generalist feeder and the most abundant species on Mauna Kea, was the only native species to maintain a stable population. The Japanese white-eye (Zosterops japonicus), a well-entrenched generalist and one of the three most common introduced species, declined. Drought prevailed in 74% of months during 2000–2011, and dry conditions contributed to the recent decline of the palila by reducing the annual māmane (Sophora chrysophylla) seed pod crop, which influences palila breeding and survival. Sustained browsing by introduced ungulates also lowered habitat carrying capacity, and their elimination should reduce the effects of drought and promote forest restoration. Our results illustrate how the feeding ecology of a species can influence its response to interacting environmental perturbations, and they underscore the value of long-term monitoring to detect population trends of sensitive species.

Ecology and Population Dynamics ofSclerocactus Mesae-Verdae(Boissev. & C. Davidson) L.D. Benson

The population dynamics of Sclerocactus mesae-verdae were documented annually in 3 plots over 20 years in southwestern Colorado. Demographic studies of this duration are rare but they are necessary to gain a more accurate estimate of population trends in long-lived desert species. Sclerocactus mesae-verdae was federally listed as threatened in 1979; this study was initiated in 1986 with the objective of determining whether Colorado populations were growing, declining, or stable. Data collected yearly around 1 May included diameter, vigor, and flower/fruit counts for 1629 stems belonging to 659 plants. We used regression analysis to estimate the mean, variance, and average popula- tion growth rate for each plot. Observations made throughout the study suggested that the cactus responded strongly to climatic variables, especially precipitation and temperature, and that 2 of the 3 subject populations were subject to periodic devastation by a longhorn beetle (Moneilema semipunctatum). These observations led us to attempt to correlate signifi- cant mortality (beetle-caused) or recruitment events to climate variables. We found that the cactus populations appear to be roughly stable to increasing slightly, possibly due to several wet springs and warmer-than-average winter temperatures since 1992. However, the warming trend also favors beetle predation, which overall presents a concern for the species' long-term survival. We conclude that 20 years may not be long enough to clarify large-scale climate influences on the persistence of long-lived desert species.