Morphological and geographic variation of the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications

The relationship in geographical distribution and morphological variation of leaflet width and length (diagnostic trait), between and within populations of Dioon edule Lindl., has been investigated throughout its known range in eastern Mexico (from the states of Nuevo León to Veracruz, north to south, respectively). A total of 1832 leaflets were measured for width and length from 154 plants distributed amongst five populations using four leaflet replicas from each of three leaves per plant. For leaflet width and length the variation among populations indicated significant stat-istical differences ( F _4,147 = 125.83; P  < 0.0001; R ² = 92.17% and F _4,147 = 9.04; P  < 0.001; R ² = 26.8%), respectively. With respect to leaflet width, the multiple range test showed three groups with a north to south distributional relationship along the range of the species. The correlation coefficient among paired populations, respect to geographical distance and the absolute value of the mean difference of leaflet width in each population, was positive, and different from zero ( r  = 0.82; P  = 0.013). A great variation of important ecological and evolutionary parameters was shown.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 465–470.     

Genetic diversity through life history of Dioon edule Lindley (Zamiaceae, Cycadales)

The distribution of genetic diversity and structure for three populations of Dioon edule Lindley (Zamiaceae) at Monte Oscuro (MO), El Farallón (EF) and Rancho del Niño (RN) in Veracruz, Mexico was studied using 20 allozyme loci, considering four life history classes: seeds, seedlings, juveniles and adults. The MO population is genetically less diverse than the EF and RN populations. Total and local inbreeding differ significantly between life history classes. An increment of inbreeding among all classes was observed, and genetic differentiation among populations was higher in seeds and seedlings than in juveniles and adults. In terms of percentage of polymorphic loci, the MO seeds showed least (80%), followed by RN (95%) and EF had the highest values (100%), probably because of a reduction in effective population size and habitat fragmentation processes. In this context, the mean effective population size was 23.2 ± 11.3 for all populations. We conclude that seed cohorts in EF and RN represent a reservoir of genetic diversity within these two populations. Also, preservation of adult plants is an essential aspect to consider in management and conservation efforts for populations of Dioon edule in natural conditions.     

Population genetics of Dioon edule Lindl. (Zamiaceae, Cycadales): biogeographical and evolutionary implications

Dioon edule Lindl. (Zamiaceae) is a cycad endemic to Mexico, that occurs as one species D. edule and the geographical variety D. edule var. angustifolium (Miq.) Miq. Dioon edule has a north to south distribution in eastern Mexico. In this study, we analysed 14 allozymic loci in eight populations of D. edule from its total distribution range by sampling all known populations. Patterns of diversity and genetic variability, within and among populations, were obtained. The mean number of alleles per locus ( A ) was 1.44 and the percentage of polymorphic loci was relatively high ( P  = 54.78). The mean observed ( H _O ) and expected heterozygosity ( H _E ) were 0.27 and 0.24, respectively. F -statistics revealed an excess of heterozygous genotypes, locally and globally ( F  = −0.17 and f  = −0.27, respectively). The genetic variation explained by differences among populations was only 7.5%. We also detected a negative relationship between genetic diversity and latitude. On average, the gene flow between population pairs was relatively high ( Nm  = 2.98); furthermore, gene flow between population pairs was significantly correlated with geographical distances ( r  = −0.38, P  = 0.025). Therefore, patterns of genetic diversity in D. edule appear to be associated with the post-Pleistocene spread of the species, from its southerly (origin) to its northerly range (derived populations, including its central distribution). The biogeographical and evolutionary aspects of the results of this study are discussed. We recognize Dioon angustifolium Miq. for the northernmost disjunct populations.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 457–467     

Isolation,characterization and cross‐species amplification of microsatellite loci in the cycad genus Dioon (Zamiaceae). Potential utilization in population genetics studies of Dioon edule

Dioon edule (Zamiaceae) is an endemic Mexican cycad. Nineteen microsatellite loci were isolated from three enriched genomic libraries of D. edule var. angustifolium, D. tomasellii, and D. caputoi. Seven of these loci showed polymorphisms in D. edule. Levels of polymorphism were assessed using 16 individuals from each of seven populations throughout the range of this species. The number of alleles per locus ranged from two to five and the observed and expected heterozygosities ranged from 0.0 to 0.9821 and from 0.0088 to 0.6318, respectively. All loci show significant linkage disequilibrium. Three loci depart significantly from Hardy–Weinberg equilibrium.     

Demography of the cycad Ceratozamia mirandae (Zamiaceae) under disturbed and undisturbed conditions in a biosphere reserve of Mexico

The cycad Ceratozamia mirandae is endemic to Chiapas, Mexico. Demographic studies were made in two of its populations in the Sepultura Biosphere Reserve under different conservation conditions; in the nucleus zone “Tres Picos” (conserved) and buffer zone “La Sombra” (disturbed and under management). Spatial distribution of C. mirandae was aggregated, showed a clumped local distribution on shallow soils on steep slopes and male and female cones appear to be synchronous in both populations. The population structure was of type I (Bongers) for both sites. Individuals between the sites showed differences in growth pattern. The oldest plants (80–90 cm tall) were estimated to be about 490 years at “La Sombra”. The finite growth rate () in the buffer zone population showed a tendency for decrease whilst in the nucleus zone this estimate remained stable. The highest elasticity values lied in the transition of the first three classes of the “La Sombra” population, in “Tres Picos” this corresponded to adult plants between 20 and 30 cm tall. Given the above, it is proposed that in the nucleus zone, reproductive adults should be of highest conservation priority, whereas in the buffer zone seedling reintroduction should be carried out regularly until the population increases. We recommend an IUCN Red List category of Vulnerable (VU C, 2a), largely due to difficult-to-control destructive annual forest fires that occur in this Reserve.     

Allozyme variation in the three extant populations of the narrowly endemic cycad Dioon angustifolium Miq. (Zamiaceae) from North-eastern Mexico

BACKGROUND AND AIMS: Dioon angustifolium was considered within D. edule. Recent morphometric and allozyme studies on D. edule have shown that D. angustifolium has originated from geographic isolation and is therefore considered to be a separate species. This cycad is endemic to north-eastern Mexico and is known only from three populations in the Sierra Madre Oriental mountain chain. Its populations are small when compared with its southern relative D. edule. In this study, genetic variation was determined within and between populations of D. angustifolium and the genetic consequences of habitat fragmentation and isolation of populations of this species were assessed. METHODS: Allozyme electrophoresis of 14 presumptive loci was used. The data were analysed with statistical approximations for estimating genetic diversity, structure, gene flow and recent genetic bottlenecks. KEY RESULTS: Means and standard deviations of genetic diversity estimators were: number of alleles per locus (A = 1.67 +/- 0.23), percentage of polymorphic loci (P = 52.4 +/- 23 %) and expected heterozygosity (H(E) = 0.218 +/- 0.093). The genetic variation attributable to differences among populations was 16.7 %. Mean gene flow between paired populations was Nm = 1.55 +/- 0.67, which is similar to that reported for endemic plant species of narrow geographical distribution and species with gravity-dispersed seed. A recent bottleneck is detected in the populations studied. CONCLUSIONS: Dioon angustifolium presents high levels of genetic diversity compared with other cycad species, in spite of small population sizes. The recent bottleneck effect did not effectively reduce the genetic variation to the extent of eliminating these populations. The distribution of D. angustifolium appears to be the result of historical biogeographical effects related to the Pleistocene glaciations. It is recommended that this species be catalogued in the IUCN Red List of Threatened Species and conservation efforts be made to preserve it.     

Genetic diversity and structure of the cycad Zamia loddigesii Miq. (Zamiaceae): implications for evolution and conservation

The genetic diversity and structure of four populations of the cycad Zamia loddigesii were studied throughout its range in Mexico. Allozyme electrophoresis of 15 loci was conducted. The mean number of alleles per locus was 1.80 ± 0.09, the percentage of polymorphic loci was 66.6 ± 5.4, and the expected heterozygosity was 0.266 ± 0.02. The results indicated that the genetic diversity was relatively higher, with respect to tropical tree species and other cycads. The genetic variation explained by differences among populations was 18%. On average, gene flow between paired populations was similar ( Nm  = 1.6) to other tropical forest trees and cycad species. Our results indicated that the geographical isolation among populations of Z. loddigesii generated allele loss, as well as a clinal variation in the frequencies of two loci ( MDH and MNR2 ), in relation to the latitudinal distribution of populations. The populations have become fragmented due to increasingly higher pressure of habitat conversion and disturbance. The importance of the establishment of sanctuaries and protected areas and a reduction in deforestation is highlighted in this research as a way of preserving the high genetic diversity of this and other endemic species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 533–544.     

Speciation along a latitudinal gradient: The origin of the Neotropical cycad sister pair Dioon sonorense–D. vovidesii (Zamiaceae)

Latitude is correlated with environmental components that determine the distribution of biodiversity. In combination with geographic factors, latitude‐associated environmental variables are expected to influence speciation, but empirical evidence on how those factors interplay is scarce. We evaluated the genetic and environmental variation among populations in the pair of sister species Dioon sonorense–D. vovidesii, two cycads distributed along a latitudinal environmental gradient in northwestern Mexico, to reveal their demographic histories and the environmental factors involved in their divergence. Using genome‐wide loci data, we determined the species delimitation, estimated the gene flow, and compared multiple demographic scenarios of divergence. Also, we estimated the variation of climatic variables among populations and used ecological niche models to test niche overlap between species. The effect of geographic and environmental variables on the genetic variation among populations was evaluated using linear models. Our results suggest the existence of a widespread ancestral population that split into the two species ~829 ky ago. The geographic delimitation along the environmental gradient occurs in the absence of major geographic barriers, near the 28th parallel north, where a zonation of environmental seasonality exists. The northern species, D. vovidesii, occurs in more seasonal environments but retains the same niche of the southern species, D. sonorense. The genetic variation throughout populations cannot be solely explained by stochastic processes; the latitudinal‐associated seasonality has been an additive factor that strengthened the species divergence. This study represents an example of how speciation can be achieved by the effect of the latitude‐associated factors on the genetic divergence among populations.     

Diversity and genetic structure of three species of Dioon Lindl. (Zamiaceae, Cycadales) from the Pacific seaboard of Mexico

We have estimated levels of genetic diversity and partitioning in the Mexican endemic cycad species Dioon sonorense, Dioon tomasellii, and Dioon holmgrenii, whose populations are exclusively distributed along the Pacific seaboard. For the three species, the patterns of variation at 19 allozyme loci in a total of 11 populations were evaluated. The average number of alleles per locus was in the range 2.05–1.68, corresponding to the northernmost population of D. sonorense (Mazatán), and the southernmost population of Dioon holmgrenii (Loxicha), respectively. In turn, the percentage of polymorphic loci peaked (94.73) in the El Higueral and Altamirano populations of Dioon tomasellii, and was estimated to be lowest (57.89) in the Loxicha population of D. holmgrenii. The mean expected heterozygosis varied markedly between taxa, with relatively high indices for D. sonorense and D. tomasellii (H_E = 0.314 and 0.295, respectively) and substantially lower values for D. holmgrenii (H_E = 0.170). Comparison of the inferred genetic structure based on F‐statistics for the three species also indicated differences along the north‐south Pacific seaboard axis. For D. sonorense and D. tomasellii, local inbreeding (F_IS) was zero but global inbreeding (F_IT) values were positive and significantly different from zero (0.130 and 0.116, respectively). By contrast, values of both F_IT and F_IS were negative and significantly different from zero (?0.116 and ?0.201, respectively) for D. holmgrenii. The genetic differentiation between populations (F_ST) had positive values in all taxa and corresponded with their geographic location along the north‐south axis: according to this statistic, D. sonorense was the most differentiated species (F_ST = 0.151), D. tomasellii had intermediate values (F_ST = 0.145), and D. holmgrenii was the less differentiated taxon (F_ST = 0.069). Finally, a phenogram representing Nei's genetic distances among populations displayed three major groups, each one corresponding to each of the studied species. Within D. tomasellii (of intermediate geographic distribution), a further division into two clusters corresponded precisely to the pair of populations that are geographically divided by the Trans Mexican Neovolcanic Mountains. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 765–776.     

Population dynamics of two Scottish Ultramafic (serpentine) rarities with contrasting life histories

Summary

The paper reports demographic studies of the endemic Cerastium nigrescens and the very rare Arenaria norvegica ssp. norvegica on the Keen of Hamar ultramafic outcrop on Unst, Shetland from June 1994 to November 1996. Plants of Cerastium nigrescens showed a Deevey type II curve and mature plants had a half-life of 3.8 years. Plants of Arenaria norvegica ssp. norvegica showed a Deevey type I curve with high mortality after flowering in the second year. There was some evidence of increased mortality during droughts but this had little impact on the total population. Seed production and seedling recruitment for both species was good throughout the study period. Seed bank measurements ranged from 12–13 m² for Cerastium nigrescens and 24–43 m^-2 for Arenaria norvegica ssp. norvegica. The study showed that there was no immediate threat to the populations of the two species but because of their isolated occurrence they are susceptible to extinction and should be carefully monitored.     

Population modelling of Gelidium sesquipedale (Rhodophyta, Gelidiales)

A matrix population model of Gelidium sesquipedale, a commercial agarophyte from the Northeast Atlantic, was developed based on demographic data obtained during two years in a commercial stand of Cape Espichel, Portugal. G. sesquipedale individuals were classified into categories such as life cycle phase, spores, juveniles and adult frond size, because the species vital rates, fecundity, fertility, survival, growth and breakage depend on them. We also exemplify the use of a user-friendly modelling software, Stella, to develop a structured-population model. This is the first time this software has been used to model the demography of seaweed populations. The Stella model developed here behaved very similarly to the matrix model, because of its particular construction, which causes the forcing functions to be discrete rather than continuous. The relative importance of spore recruitment and vegetative growth of new fronds in both population growth and population structure was investigated. Elasticity analysis suggests that vegetative recruitment is the most important demographic parameter controlling population growth together with survival and transitions between juveniles (1–6 cm fronds) and class 1 fronds (6–9 cm fronds). On the other hand, sexual reproduction may, by itself, efficiently control the relative proportion of gametophytes and tetrasporophytes in the population, even though its contribution to recruitment is extremely small. A 40% difference in the growth rates of gametophyte and tetrasporophyte submatrices resulted from natural differences in spore recruitment rates. This revised version was published online in June 2006 with corrections to the Cover Date.     

Assessment of life history parameters of Aspidiotus nerii (Hemiptera: Diaspididae) to improve the mass rearing of Aphytis melinus (Hymenoptera: Aphelinidae)

The biological control of Aonidiella aurantii (Maskell) on citrus can be achieved with periodic releases of the parasitoid Aphytis melinus DeBach. A. melinus is normally reared on parthenogenetic strains of the scale Aspidiotus nerii Bouché. The developmental rate, crawler production and survival of A. nerii were studied at two temperatures (25±1 and 30±1°C) and two levels of relative humidity (RH; 55±5 and 85±5%) on squash. Temperature had an important effect on developmental rate, but RH did not. At 30°C, no growth was observed and no crawlers were produced. At 25°C, development of the L1, L2 and young females’ stages required 24.4±0.7, 11.1±0.8 and 13.2±0.3 days, respectively. At 25°C, times until the appearance of mature females, the start of crawler production and the peak of crawler production were 48.7±0.1, 50.1±0.7 and 63.3±1.0 days, respectively. Crawler production lasted 42.6±1.9 days, and the 50% production level was reached on day 13. Initially, crawler survival was higher at 30°C (65.9±2.8%) than at 25°C (51.7±4.8%), but by the end of development survival was much higher at 25 than 30°C (88.0±2.1 vs. 22.9±2.7%). RH had no effect on either initial or final survival. Average progeny production was of 28.0±2.8 crawlers per female at 25°C. The relationship between the weight of groups of crawlers and their number was: Number=1031+835,500×weight of group (g) (R ²=0.826), which can assist in colony management. The importance of selecting the correct strain of A. nerii is emphasised.     

Population dynamics of an endangered heathland shrub,Epacris stuartii (Epacridaceae): Recruitment,establishment and survival

The only known population of the endangered shrub Epacris stuartii Stapf was studied from 1994 to 2001 using demographic census techniques. The effects of substrate, a fire and a storm on the emergence and survival of seedlings and the survival of established plants of different sizes were examined using failure‐time analyses and logit‐linear models. Ninety‐five per cent of seedling emergence was delayed until the second post‐fire spring, an unusual response among species with persistent soil seed banks. Mortality of seedlings was extreme compared with larger‐seeded species, but diminished significantly with age. Seedling mortality varied significantly between substrates: 40% of seedlings persisted for more than 5 years in mineral soil, whereas less than 10% lived more than a year on rock and intermediate substrates. However, seedling numbers and local densities were lower on soils than other substrates. Background mortality of established plants was lower on soil and intermediate substrates (0.5% per year) than on rock (3% per year). Small plants may be more susceptible than large plants on rock, but not on soil. Both the fire and the storm resulted in elevated mortality of established plants. The population exhibited a variable response to fire, with plants on rock and intermediate substrates behaving as obligate seeders, whereas plants in soil resprouted. This appears to be the first report of microhabitat variation in fire response at sympatric scales. The effects of the storm were apparently independent of substrate and plant size. The essentially independent disturbance regimes comprising recurring fires and storms are likely to have a profound effect on the long‐term population dynamics of E. stuartii. Over the 7‐year census period, recruitment has failed to compensate for mortality, resulting in a 30% net decline in the population. The demographic census has proved to be crucial in the detection and diagnosis of this decline.     

Population dynamics of the rare plant Kosteletzkya pentacarpos (Malvaceae): a nine-year study

Rare plant species have extremely narrow distributions that can be reduced to a single or few populations. The rare long-lived plant Kosteletzkya pentacarpos is one such species because only two extant localities are known in the western Mediterranean. In this study, we analyse the population dynamics over nine years of the only population known in north-east Spain, which is located at the Llobregat delta (Barcelona). We collected basic demographic data to build a transition matrix model. We computed population growth rates λ and their confidence intervals for each year of study. We conducted elasticity and variance decomposition analyses to determine the relative importance of vital rates to overall population dynamics. On average, the K. pentacarpos population exhibited an increasing dynamics. Survivorship of adult plants contributed the most to each λ, whereas temporal variance in fecundity and juvenile fate explained the observed variation in λ. Despite the increasing dynamics of K. pentacarpos , important reductions in fecundity resulting from biotic agents and recruitment owing to habitat limitations are constraints for population growth. We conclude that the knowledge generated in this long-term study should be used to create new K. pentacarpos populations at the Llobregat delta in order to minimize the risk of extinction following catastrophic events that are nearly impossible to predict.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 455–462.     

Life history, life table, habitat, and conservation of Byasa impediens (Lepidoptera: Papilionidae)

This article investigates the biology of Byasa impediens, presenting its life-table data and analyzing its habitat requirements and the key factors threatening the survival of this species. This study also aims to detect specific protection methods to guarantee the long-term survival of Byasa impediens in Baishuijiang Reserve. Byasa impediens is bivoltine in Baishuijiang Reserve. The pupae overwinter on shrubs or on branches of trees. The eclosion of the first generation starts in mid-April. The adults of the first generation emerge in large numbers in mid-late May, and the second generation emerges from late June to mid-July. The two generations overlap. The adult males emerge 7–10 days earlier than the adult females. Their flight behavior is determined by factors such as perching along small rivers and gullies, and visiting flowers. The males are strong fliers. On the contrary, the flying ability of the females is weak; therefore, they just visit flowers, mate, and lay eggs near the natal area. The ratio of female to male is 1:4.1. The maximum lifespan of the males is 26 days, with an average of 6.9 days, whereas the maximum lifespan of the females is 21 days, with an average of 7.6 days. The pregnant eggs per female are 31.5 on average. The incubation period of the first generation is 12–14 days, whereas that of the second generation is 7–9 days. The larvae feed mainly on Aristolochia heterophylla. The larval period of the first generation lasts for 30 days with five instars and that of the second generation lasts for 30–40 days with five or six instars. The pupal period of the first generation begins in early June and lasts for 20–26 days whereas for the second generation, it begins between late July and late September. The adults prefer the following nectar plants: Albizzia julibrissin, Bauhinia glauca, Clerodendrum bungei, and Sambucus chinensis. The plant Aristolochia heterophylla is distributed at an altitude of 900–1680 m, and the most suitable range is 1200–1500 m. The host plants grow mainly along the paths and along the borders of forests where the canopy is rather open and shrubby undergrowth is found. The plant can hardly be found when the canopy density of the forest is greater than 80%. The elevation range most suitable for the larvae is 1200–1500 m. The ideal habitat of host plants also seems to be the ideal habitat of Byasa impediens. The key factors that adversely affect the population of Byasa impediens are loss and deterioration of habitats. The loss and deterioration of the habitats result in a decrease in the numbers of host plants and a more restricted distribution of the potential habitats. The habitat is easily influenced by anthropogenic activities, such as herding, cultivating, and using pesticides, which in turn influences the growth of the host plant Aristolochia heterophylla and the larvae of butterflies. Abnormal climatic conditions and natural enemies are the key factors affecting population density. The hot and dry weather in summer and the heavy rain in autumn considerably reduce the survival rate of eggs and larvae. The ichneumon parasitoids reduce the survival rate of the over-wintering pupae. The primary natural enemies of the larvae include spiders, earwigs, wasps, bugs, and ichneumon parasitoids. Other natural enemies of pupae and adults are birds. The most important conservation measures are preservation and reconstruction of the natural habitat, which includes rebuilding forests, enhancing management, enforcing existing laws, and developing eco-tourism. Creating a core-patch near all patches at a central area is also an important measure for conservation. In the most ideal habitat, appropriate shrub cutting can increase the growth of host plants, thereby promoting expansion of the Byasa impediens population.     

How has the remnant population of the threatened frog Leiopelma pakeka (Anura: Leiopelmatidae) fared on Maud Island,New Zealand,over the past 25 years?

Despite widespread global reports of declining amphibian populations, supporting long‐term census data are few, limiting opportunities to study changes in numbers and survival over time. However, in New Zealand, for the past 25 years (1983–2008), we studied Leiopelma pakeka, a threatened, terrestrial frog that inhabits rocky boulder banks under forest on Maud Island. Using night sampling at least annually on two 12 × 12 m plots, we had 5390 captures of 1000+ individuals, 327 on one plot (grid 1), 751 on the other (grid 2). The mean (±SE) number of frogs found per night was 11.3 (±0.6) on grid 1 and 25.6 (±1.4) on grid 2. We used capture‐recapture models to estimate population size, proportion of animals remaining beneath the surface and survival rate. The mean (±SE) population estimate was 131 (±14.7) frogs on grid 1 and 367 (±38.7) on grid 2. Over 25 years the estimated population increased on grid 1 and fluctuated on grid 2. Some frogs were captured on most sampling visits, others less often, evidently failing to emerge from cover each visit. Using a combination of open and closed population models, we estimated the mean (±SE) proportion remaining underground was 0.63 (±0.12) on grid 1 and 0.53 (±0.07) on grid 2. Our research represents one of the longest‐run population studies of any frog, and we recorded significant longevity, two males reaching 35+ and 37+ years, a female 34+ years. No significant differences occurred between mean annual survival rates of apparent females and males, or between the two sites. The number of toes clipped for individual identification had little influence on the return rate, once the effect of time of first capture was removed.     

Survival and recruitment of seedlings and suckers of trees and shrubs of the Australian arid zone following habitat management and the outbreak of Rabbit Calicivirus Disease (RCD)

Abstract Recruitment in many shrub and tree species in arid Australia is limited by domestic and feral animal grazing. The outbreak of Rabbit Calicivirus Disease (RCD or RHD) in late 1995 at Kinchega National Park (NP) in arid western NSW, Australia, coincided with intensified warren ripping and other rabbit (Oryctolagus cuniculus) control efforts. We monitored changes in rabbit numbers in response to these factors using spotlight counts and dung‐pellet counts. Rabbit populations declined initially, and were low for the remainder of the study. To assess the impact of rabbit control on vegetation, we examined whether recruitment of seedlings or vegetative suckers was occurring at Kinchega NP, following the arrival of RCD; how long such recruits were likely to survive under current grazing pressures; and whether the magnitude of current seedling and vegetative sucker recruitment and survival is greater than available data prior to RCD and extensive warren control. We followed the survival of individual seedlings and newly emerged suckers of six shrub or tree species, most of which are considered to be at risk of local decline. Three levels of caging were used to exclude all mammalian grazers; all mammalian grazers except rabbits; and no mammalian grazers. Pooled cohorts of seedlings and suckers were analysed using failure‐time analyses. During the course of the study, suckering was observed in four species (Acacia carneorum, Alectryon oleifolius, Casuarina pauper and Santalum acuminatum), with seedlings observed in the other two species (Dodonaea viscosa and Acacia ligulata). Survival of suckers of some species was slightly greater than pre‐RCD estimates, but in general, a pattern of little or nil recruitment is likely in suckers exposed to rabbits or to all grazing mammals. Seedling survival was particularly low regardless of the level of exclusion, largely due to desiccation. Reduction of grazing impacts may only allow recruitment into populations of species reliant on seedlings under more favourable climatic circumstances than experienced in this study, while the probability of successful recruitment into populations of suckering species in western NSW continues to be low even at very low rabbit densities.