Matrix analysis to evaluate sustainability: The tropical tree Aquilaria crassna, a heavily poached source of agarwood

We used size-structured Lefkovitch projection matrix analysis to predict future trends in the survival of Aquilaria crassna (Thymelaeaceae), a tropical evergreen forest tree that has been highly sought after for its valuable aromatic wood (agarwood) for millennia. Data on growth, damage to trees by poachers, fruit production, seed dispersal and seedling recruitment were collected from a 30-ha plot in Khao Yai National Park, central Thailand that had seen moderate poaching. The population asymptotic growth rate, λ_a, and transient growth rate, λ_tr, found from using the matrix to project the observed population 48 years, were 1.002 and 1.005, respectively, with 95% confidence intervals of [0.985, 1.016] and [0.985, 1.023]. The stable size distribution obtained from the matrix was reasonably similar to the observed size distribution, suggesting that at the time of the study the population was not far from equilibrium. Sensitivity analysis and simulations of poaching on adult trees indicate that both λ’s are very sensitive to the removal of adult trees and the growth of preadult trees. In particular, the increase in tree mortality and decrease in preadult growth rate caused by agarwood collection seen in some areas could cause extirpation of the population. While in such cases the population appears to be poised on the brink of decline, several factors that we could not evaluate could alter its fate. First, adult deaths could stimulate recruitment of young under the parent trees; second, there is marked year-to-year variation in fruiting success and possibly recruitment; third, there is considerable spatial variation in tree density and recruitment, suggesting that attempts to evaluate future success need to encompass larger spatial and time scales.     

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.     

Aspects of the management of cheetahs, Acinonyx jubatus jubatus, trapped on Namibian farmlands

The Namibian cheetah population has recently undergone serious decline due to human-mediated removals, and investigating the rates and causes of such removals is an important aspect of the future management of cheetah populations outside protected areas. We examined cheetahs that were reported live-trapped or killed on Namibian farmlands between 1991 and 1999. A perceived threat to livestock or game led to the vast majority of live captures and to almost half of the cheetah deaths investigated. Despite this, livestock predation from cheetahs appeared to be minimal, and was usually perpetrated by cheetahs with injuries. Most of the cheetahs were trapped in groups, and cheetahs’ relative sociality leads to the easy removal of entire social units. Long-term monitoring must include detailed consideration of these indiscriminate removals, as they involve many cheetahs, fluctuate between years, often go unreported, and are likely to have a serious impact on cheetah populations outside protected areas.     

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.     

Factors influencing survival and long-term population viability of New Zealand long-tailed bats (Chalinolobus tuberculatus): Implications for conservation

A population viability analysis is important for the management of endangered populations and requires the estimation of survival parameters. The long-tailed bat (Chalinolobus tuberculatus) is one of only two native terrestrial mammals currently found in New Zealand and is classed as vulnerable. Its viability in temperate beech (Nothofagus) forest, Eglinton Valley, Fiordland, New Zealand was estimated using mark-recapture data collected between 1993 and 2003 using the Program MARK. Survival was estimated based on a total of 5286 captures representing 1026 individuals. Overall annual survival varied between 0.34 and 0.83 but varied significantly among three sub-populations and with sex and age. Females generally had a higher survival rate compared to males; and adults had higher survival relative to juveniles. Survival of all bats was lower in years when the number of introduced mammalian predators was high and when the winter temperature was warmer than average. High numbers of introduced predators occurred during three of the 10 years in the study. Climate change may mean that the conditions that promote high predator numbers may occur more frequently. A preliminary population viability analysis using a projection matrix on the overall adult female population showed an average 5% decline per year (λ = 0.95). Increased predator control targeting a range of predators is required in years when their numbers are high in order to halt the decline of this population of long-tailed bats. Population estimates using minimum number alive estimates supported the population estimates derived from Program MARK and a population viability analysis using matrices.     

Are populations of the candy barrel cactus (Echinocactus platyacanthus) in the desert of Tehuacán, Mexico at risk? Population projection matrix and life table response analysis

Echinocactus platyacanthus is a candy barrel cactus endemic to Mexico and an endangered species owing to its exploitation and the destruction of its habitat. The population dynamic of this species is analyzed using matrix models. Three consecutive censuses were carried out (1997, 1998, and 1999) for six populations of this species in the Tehuacán-Cuicatlán Biosphere Reserve. Fruit contain many seeds (mean = 171 ± S.E. 11.03 seeds/fruit); seedling establishment and survival are low (2 × 10⁻⁶), and fecundity increases as the diameter of the individuals increases (62 seeds in adult 1-4322 in adult 4). The rates of population growth (λ) range from 0.9285 to 1.0005. Elasticity values for demographic processes indicate that the stasis of the adults is the greatest contribution (S = 0.982), followed by growth (G = 0.017) and fecundity (F = 0.001) to λ. The populations are located in the lower left corner of the demographic triangle; however, there are variations for a given population from one year to the next. Life table response experiments indicate that although there are local variations, the most important differences in the values of λ between populations and between years are associated with changes in the stasis of the adults. The disturbance index is not directly related to population density or to the current value of λ. The protection of adult E. platyacanthus must be taken into account for the management of this species and its conservation in the study area.     

Demographic analysis of a rare columnar cactus (Neobuxbaumia macrocephala) in the Tehuacan Valley, Mexico

In this study we used population projection matrices to evaluate the conservation status of Neobuxbaumia macrocephala, a columnar cactus endemic to a small region in the Tehuacan Valley, in central Mexico. Demographic data included 2-year observations on growth, fecundity and survival of individuals classified by size. Our results indicate that the population is comprised of 70% juveniles. Population growth rate was 0.979 and 0.994 for the 1997/1998 and the 1998/1999 periods, respectively. The slight increase in λ in 1998/1999 was a result of increased fecundity and seedling survival. The highest elasticity values correspond to the survival of large/old individuals. Numerical simulations were performed by changing the value of particular matrix entries and directly evaluating their effect on λ. Population growth rate reached values above unity only when either fecundity or seedling survival probability were increased 10-fold. Given these limitations for population growth, along with its limited distribution range and low population densities, we propose N. macrocephala to be classified as a rare species and to promote its conservation by favoring management practices aimed to increase germination and seedling establishment success.     

Demography of the Namibian cheetah, Acinonyx jubatus jubatus

Namibian cheetahs have suffered, and continue to suffer, high levels of removal due to conflict with local farmers, and it is important to understand the demography of this population in order to determine its likely persistence. Examination of cheetahs reported live-trapped or killed by local farmers, combined with subsequent information from radio-telemetry, allowed demographic parameters such as sex ratios, age and social structure, litter size, interbirth intervals and survivorship to be estimated for cheetahs on Namibian farmlands. Cub mortality was relatively low, but adult mortality was high, particularly for males, and peaked at 5-6 years of age. Neither marking nor relocating cheetahs seemed to affect survivorship, and there was no difference in survivorship between the sexes. Time spent in captivity did not appear to affect survival after release. These findings will be useful in formulating recommendations regarding the conservation and sustainable utilization of cheetah populations outside protected areas.     

Impacts of chronic marine oil pollution and the murre hunt in Newfoundland on thick-billed murre Uria lomvia populations in the eastern Canadian Arctic

We developed a deterministic and stochastic age-based matrix projection population model to assess and quantify the impact of mortality caused by chronic oil pollution and legal hunting on thick-billed murre Uria lomvia populations breeding and wintering in eastern Canada. We calculate the potential population growth rate in the absence of anthropogenic mortality sources using a modeling technique that translates absolute number of birds killed from anthropogenic mortality to potential survival rates in the absence of these anthropogenic impacts. The intrinsic growth rate of the deterministic matrix based on vital rates from Coats Island (λ_d=1.0102), as well as the stochastic growth rate (λ_s=1.0098, 95% C.I. 0.9969-1.0226), matched observed population trends. Hunting mortality reduced population growth rate by 0.020 (0.012-0.039), oiling mortality reduced population growth rate by 0.025 (0.012-0.039). Combined these sources reduced the population growth rate by 0.047 (0.033-0.610). Although thick-billed murre populations are stable or slowly growing in eastern Canada, anthropogenic sources of mortality are reducing the ability of the population to grow, and increase vulnerability in these populations to changes in their environment and other pulse perturbations. Our modeling technique could be used to assess specific anthropogenic impacts on populations where a vital rates and numbers killed are known, but no long-term trend information is available.     

Potential biological removal of albatrosses and petrels with minimal demographic information

Seabirds such as albatrosses and petrels are frequently caught in longline and trawl fisheries, but limited demographic data for many species creates management challenges. A method for estimating the potential biological removal (the PBR method) for birds requires knowledge of adult survival, age at first breeding, a conservation goal, and the lower limit of a 60% confidence interval for the population size. For seabirds, usually only the number of breeding pairs is known, rather than the actual population size. This requires estimating the population size from the number of breeding pairs when important demographic variables, such as breeding success, juvenile survival, and the proportion of the adult population that engages in breeding, are unknown. In order to do this, a simple population model was built where some demographic parameters were known while others were constrained by considering plausible asymptotic estimates of the growth rate. While the median posterior population estimates are sensitive to the assumed population growth rate, the 20th percentile estimates are not. This allows the calculation of a modified PBR value that is based on the number of breeding pairs instead of the population size. For threatened albatross species, this suggests that human-caused mortalities should not exceed 1.5% of the number of breeding pairs, while for threatened petrel species, mortalities should be kept below 1.2% of the number of breeding pairs. The method is applied to 22 species and sub-species of albatrosses and petrels in New Zealand that are of management concern, of which at least 10 have suffered mortalities near or above these levels.     

Successful reintroductions of the endangered long-lived Sargent’s cherry palm, Pseudophoenix sargentii, in the Florida Keys

The 1991-1994 reintroductions of Florida endangered Pseudophoenix sargentii to 13 Florida Keys sites represent a rare example of a successful multi-agency long-term effort to conserve a long-lived palm. To assess reintroduction success, we compared population demographics with and without reintroduced plants and conducted population viability analyses. Since 1991, the wild population has increased 6.4-fold. Survival from 2000-2004 was 94%, growth was positive (λ = 1.013), and there was no predicted extinction risk. Recent wild population growth is attributed to good seedling recruitment and removing the greatest threats. After 14 years, reintroductions had 43% survival, increased total plants in the wild by 27%, and expanded the species’ distribution. Reintroduced plants had faster maturation rates, improved population age structure, and enhanced population growth (λ = 1.032). Success varied with transplant year, location, microsite, and original transplant size. Failures in 1991 and at some historic sites emphasize the need for a multi-year, multi-site approach to reintroductions to buffer against stochastic losses. Rockland hammocks and the tops of coastal berms had greatest plant growth and survival. Large transplants had the greatest survival. Because no reintroduced plants are reproductive, transitions between stages are extremely slow, and plants may require >30 years to mature, continued institutional dedication to long-term monitoring will be required to assess whether the populations are self-sustaining. Horticultural expertise and ex situ collections complimented support of land managing agencies for the species’ preservation. These first rare plant reintroductions to Florida State Parks opened avenues for more plant conservation efforts and public interpretation.     

Ruffed grouse population dynamics in the central and southern Appalachians

Ruffed grouse (Bonasa umbellus; hereafter grouse) populations in the central and southern Appalachians are in decline. However, limited information on the dynamics of these populations prevents the development of effective management strategies to reverse these trends. We used radiotelemetry data collected on grouse to parameterize 6 models of population growth to: (1) determine the pattern of growth in these populations, and (2) identify the demographic rates most important to growth. Trend estimates from population models were most similar to trend estimates derived from Breeding Bird Survey and Christmas Bird Count data when models incorporated either a reproductive or survival event. These events randomly increased fecundity or survival, respectively, to their empirical maxima on average once every 5 years. Reproductive events improved estimates on areas dominated by mixed mesophytic forest, while survival events characterized population growth on oak (Quercus spp.)-dominated sites. The finite rate of increase (λ) was most sensitive to brood survival followed by adult and juvenile non-breeding survival on most sites. However, brood survival was low (<0.35 female chicks/hen survived to week 5), and elasticity analyses indicated λ responded more strongly to proportionate change in non-breeding and breeding survival rates of adults and juveniles than any reproductive variable. Life stage analyses corroborated this result. At baseline values, survival of adults and juveniles may be the main determinants of growth in these populations, and reproduction may not be adequate to compensate for these losses. Therefore, population growth above baseline levels may be regularly needed to restock these populations. Researchers have hypothesized that population dynamics may differ between mixed mesopytic and oak-dominated sites due to differences in forage quality and quantity. Thus, a potential mechanism for the increases in λ needed to sustain populations on mixed mesophytic forest sites is the greater fecundity observed during years with high oak or beech (Fagus grandifolia) mast abundance. The availability of this high quality forage allows hens to enter the breeding season in better condition and realize higher fertility. Alternatively, on oak-dominated sites, population growth increases may also be a product of higher non-breeding survival of birds in mast years, when birds do not need to range as far to forage and can limit their exposure to predators.     

The status and conservation of the cheetah Acinonyx jubatus in Tanzania

This is the first assessment of the status of cheetahs, Acinonyx jubatus, in Tanzania since 1965. It completes a series of recent studies in Kenya, Uganda, and Malawi to provide an overall understanding of the species’ status in East Africa. Interviews with 370 informants yielded 1050 cheetah sightings. Eighty nine percent of all sightings were made in 1990-1994, and 39% of all sightings occurred in protected areas. All-adult groups contained 1.92±0.04 S.D. individuals; the average number of dependent cubs was 2.63±0.08 S.D.; and the cub-to-adult ratio was 0.34. Since the 1960s, the distribution has remained stable overall with possible reductions in central Tanzania. No definite population trends were detected. With an estimated 569-1007 cheetahs, Tanzania emerges as a sanctuary for the species worldwide. However rangelands, which may hold half of Tanzania’s cheetahs, are undergoing rapid degradation. This precarious situation calls for the establishment of a nationwide monitoring program. Distribution map and population sizes from this study could serve as a baseline for monitoring the species’ status.     

Responses of cycads with different life histories to the impact of plant collecting: simulation models to determine important life history stages and population recovery times

Collection of plants and seeds from wild populations threatens a large number of cycad species. We investigated to what extent individual life history stages contribute to population growth (λ) and compared two species with major differences in life histories in the African genus Encephalartos: Encephalartos cycadifolius, a highly persistent grassland species that resprouts after fire, and Encephalartos villosus, a relatively fast growing, non-sprouting forest species. Several harvesting scenarios impacting different sized individuals were simulated to determine the sensitivity of the two functional types to harvesting. In both species λ was most sensitive to changes in abundance of adult plants. The harvesting of seeds had minimal impact on population growth rates, whereas harvesting of adult plants led to rapid population decline. This response from two very different functional types suggests that the conservation of adult plants is critical for all cycad species. Despite similar responses to adult mortality, the two species had substantially different population growth rates. This determined recovery time after harvesting of adult individuals. Encephalartos cycadifolius is typical of highly persistent plant species associated with low levels of recruitment and unable to recover from even small losses of adults within a reasonable conservation time frame (<100 years). Our results suggest that the ability to recover from loss of individuals is an important factor that should be considered when assessing the vulnerability of wild populations to threats.     

From both sides: Dire demographic consequences of carnivorous mice and longlining for the Critically Endangered Tristan albatrosses on Gough Island

The IUCN recently uplisted the Tristan albatross (Diomedea dabbenena) to Critically Endangered. Here we present new data indicating negative population trends on Gough Island arising from low adult survival (∼91%, ascribed to accidental mortality on fishing gear) and low breeding success (averaging 32%, due to mouse predation). Fledgling production from 1979 to 2007 and numbers of incubating adults from 1956 to 2007 have both decreased by ∼1% p.a. Consecutive annual counts of incubating adults and a population model permit the first reliable estimates of the Tristan albatross population, presently 5400 breeding adults and 11,300 birds in all age- and stage-classes. Population models explore scenarios of likely demographic trends using combinations of hypothetical best-case estimates vs. observed estimates for two key parameters: adult survival and breeding success. These scenarios highlight the relative benefits to the species of eradicating mice or mitigating bycatch. The model scenario using observed estimates predicts annual growth rate at −2.85%. Adult survival rates have probably decreased in recent years, concomitant with increased longline fishing effort, which might explain the discrepancy between counts and modelled trends. Negative trends cannot be reversed by improving breeding success alone, and adult survival must exceed an improbable 97% to balance the current chick production. A worst-case scenario including a fixed number of adult deaths annually predicted a catastrophic 4.2% p.a. decrease and extinction in ∼30 years. Population growth was most sensitive to adult survival, but even using an adult survival estimate without fishery mortality, current breeding success is insufficient to maintain the population. These findings do not support the ‘compensatory mitigation of bycatch’ model (offsetting bycatch impacts by eradicating invasive species), and the impacts of both fishery mortality and mouse predation must be addressed to improve the conservation status of the Critically Endangered Tristan albatross.     

Dynamics of a black bear population within a desert metapopulation

Understanding metapopulation dynamics in large carnivores with naturally fragmented populations is difficult because of the large temporal and spatial context of such dynamics. We coupled a long-term database of visitor sighting records with an intensive 3-year telemetry study to describe population dynamics of recolonization by black bears (Ursus americanus) of Big Bend National Park in Texas during 1988-2002. This population, which occurs within a metapopulation in western Texas and northern Mexico, increased from a single pair of known breeding-age animals in 1988 to 29 bears (including 6 females of breeding age) in March 2000 (λ = 1.25/year). A migration and dispersal event in August-December 2000 reduced the population to 2 adult females and as few as 5-7 individuals. One-way movement distances from the study area during this event averaged 76 km for females (n = 7) and 92 km for males (n = 4), and 3 animals conducted migrations of at least 154, 178, and 214 km, respectively. Our observations exemplify the importance of stochastic events on demographics of small populations and highlight the potential scale of bear movement among montane islands of southwestern North America. They also provide insight into the use of dispersal data in parameterizing metapopulation models for large carnivores.     

The return of the white-tailed eagle (Haliaeetus albicilla) to northern Germany: Modelling the past to predict the future

Linking age-specific vital rates to population growth through demographic matrix models can enhance our understanding of crucial population processes, vital in a conservation context. The white-tailed eagle (Haliaeetus albicilla) population in the Federal State of Schleswig-Holstein, Germany, has been monitored since re-colonisation in 1947 and provides a well-documented example of a recovery. We test how demographic models capture growth trajectories of a recovering population and how applicable they are in guiding population management of endangered species. From 1947 to 1974, the population was stable but the growth rate predicted by an age-structured matrix model was −6.1% per annum. The small but stable population must have been maintained by immigration. From 1975 to 2008, observed and predicted population growths were very similar (6.7% and 4% per annum respectively). Elasticity and life-stage simulation analyses identified adult and pre-breeding survival as key vital rate elements. While the prospective analyses identified survival as the key vital rate influencing population growth, the increasing reproduction rate allowed the recovery to take place; thus caution is needed when prospective modelling makes management recommendations. Nevertheless, conservation efforts should address key mortality factors such as lead poisoning and collision with wind turbines. A logistic model predicted a maximum carrying capacity of 255 pairs for the Federal State, but using the highest currently observed density (1.4 pairs per 100 km²) and differences in habitat suitability, a more likely carrying capacity was estimated at 122 pairs. Under both scenarios, current population growth should slow soon.     

Dynamics of threatened goldenseal populations and implications for recovery

Goldenseal (Hydrastis canadensis) is a North American perennial clonal herb highly prized for its medicinal value. It is threatened at the northern range limit with only 20 populations known in Canada. To assist recovery planning, 13 populations were sampled to model dynamics. The fate of all ramets in one square-meter was monitored from 1998 to 2001. Transition matrices were built for 2000-2001, using three stage classes based on size and reproductive status. A six-stage pooled matrix, separating established ramets from newly produced ramets, was also constructed. Recruitment by seed was not observed and therefore excluded. The average population growth rate (λ) was 1.062 ± 0.053, which did not significantly differ from the equilibrium value (1.0) suggesting that the northern population is stationary. However, growth rates among population samples varied largely and had wide confidence intervals. Populations with λ-values less than or close to 1.0 require environmental change to increase. Recovery of goldenseal, and possibly other woodland perennials at risk, requires intervention aimed at population size augmentation, habitat optimization, and targeted dispersal.     

Dynamics of a declining amphibian metapopulation: Survival, dispersal and the impact of climate

Climate can interact with population dynamics in complex ways. In this study we describe how climatic factors influenced the dynamics of an amphibian metapopulation over 12 years through interactions with survival, recruitment and dispersal. Low annual survival of great crested newts (Triturus cristatus) was related to mild winters and heavy rainfall, which impacted the metapopulation at the regional level. Consequently, survival varied between years but not between subpopulations. Despite this regional effect, the four subpopulations were largely asynchronous in their dynamics. Three out of the four subpopulations suffered reproductive failure in most years, and recruitment to the metapopulation relied on one source. Variation in recruitment and juvenile dispersal was therefore probably driving asynchrony in population dynamics. At least one subpopulation went extinct over the 12 year period. These trends are consistent with simulations of the system, which predicted that two subpopulations had an extinction risk of >50% if adult survival fell below 30% in combination with low juvenile survival. Intermittent recruitment may therefore only result in population persistence if compensated for by relatively high adult survival. Mild winters may consequently reduce the viability of amphibian metapopulations. In the face of climate change, conservation actions may be needed at the local scale to compensate for reduced adult survival. These would need to include management to enhance recruitment, connectivity and dispersal.     

Persistence of a rare ancient cycad: Effects of environment and demography

Conservation of rare species is frequently complicated by their narrow niches and poor competitive abilities which limit their distribution to a few small populations. We studied how population size and structure of an endemic cycad of northwestern Mexico, Dioon sonorense, known to be threatened by widespread land conversion and plant extraction by humans, varied with 21 environmental variables. We also used matrix population models to show how population structure may affect its long-term persistence. Slope and soil exchangeable potassium explained a moderate proportion of the variance in the abundance of adult individuals, while abundance of adults and slope explained a large proportion of the variance in the abundance of seedlings. The strong non-linear relationships of seedling abundance with slope and adult abundance suggest threshold effects that may limit D. sonorense regeneration in less suitable environments. Modeling suggests that most of the study populations will not be viable in the long-term, except for the largest population. Modeling scenarios with large increments in fecundity and seedling survival produced modest gains in population growth. The long-term persistence of D. sonorense is shown in our study to be further threatened by: (a) small size of adult populations, (b) low-quality habitat in which most populations occur, and potentially, (c) the combined effect of low fecundity and recruitment.