The impacts of roads and other infrastructure on mammal and bird populations: A meta-analysis

Biodiversity is being lost at an increased rate as a result of human activities. One of the major threats to biodiversity is infrastructural development. We used meta-analyses to study the effects of infrastructure proximity on mammal and bird populations. Data were gathered from 49 studies on 234 mammal and bird species. The main response by mammals and birds in the vicinity of infrastructure was either avoidance or a reduced population density. The mean species abundance, relative to non-disturbed distances (MSA), was used as the effect size measure. The impact of infrastructure distance on MSA was studied using meta-analyses. Possible sources of heterogeneity in the results of the meta-analysis were explored with meta-regression.Mammal and bird population densities declined with their proximity to infrastructure. The effect of infrastructure on bird populations extended over distances up to about 1 km, and for mammal populations up to about 5 km. Mammals and birds seemed to avoid infrastructure in open areas over larger distances compared to forested areas, which could be related to the reduced visibility of the infrastructure in forested areas. We did not find a significant effect of traffic intensity on the MSA of birds. Species varied in their response to infrastructure. Raptors were found to be more abundant in the proximity of infrastructure whereas other bird taxa tended to avoid it. Abundances were affected at variable distances from infrastructure: within a few meters for small-sized mammals and up to several hundred meters for large-sized mammals.Our findings show the importance of minimizing infrastructure development for wildlife conservation in relatively undisturbed areas. By combining actual species distributions with the effect distance functions we developed, regions sensitive to infrastructure development may be identified. Additionally, the effect distance functions can be used in models in support of decision making on infrastructure planning.     

Effects of fishing protection on the genetic structure of fish populations

Marine reserves have been identified as an important tool in the management of fishery resources and their number is increasing rapidly, most of them being on islands. However, knowledge on the real effect of protection from fishing on the genetic structure of populations, the spatial scales involved, or the suitability of islands as reserves in terms of connectivity, is scarce. This paper analyses the effects of fishery protection on the genetic structure of populations of Diplodus sargus, a target species, in protected and non-protected areas of the western Mediterranean. Populations studied showed high genetic variability at spatial scales from 10¹ to 10³ km. Protected areas have significantly higher allelic richness. The lower levels of heterozygosis and higher heterozygote deficit showed by islands compared with coastal areas makes clear the importance of considering the connectivity processes when designing a MPA.     

Reduced seed production, inbreeding, and pollen shortage in a small population of a threatened tree, Magnolia stellata

We investigated how genetic factors and pollen shortage affect seed production in a small population of Magnolia stellata, a threatened insect-pollinated tree. We used microsatellite and manual pollination techniques, and compared a small population to a large one. Compared to the large population, the small population showed low allelic variation and had an F_IS significantly greater than 0 in adults, indicating that genetic deterioration, including genetic drift and inbreeding, may have occurred in adults. Manual self-pollination lowered seed production relative to manual cross-pollination to a different extent between populations: δ (the magnitude of inbreeding depression due to self-fertilization) was lower in the small population than in the large population. However, under natural pollination, the estimated embryo mortality rates after ovules self-fertilized were similar between the two populations because the primary selfing rate was higher in the small population. The ovule mortality rate due to pollen shortage and that due to factors independent of pollen shortage and selfing were both approximately 10% higher in the small population, suggesting that pollen transfer may have decreased and genetic deterioration effects may have increased in that population. These factors reduced seed production in the small population (female reproductive success = 0.3%) compared to the large population (2.6%). Our results suggest that seed production in the small population of M. stellata is strictly limited by elevated pollen shortage, selfing, and genetic deterioration in adults, which accelerate the risk of extinction.     

Fragmented but not isolated: Contribution of single trees, small patches and long-distance pollen flow to genetic connectivity for Gomortega keule, an endangered Chilean tree

Habitat fragmentation is a major threat to species survival worldwide due to genetic isolation, inbreeding depression, genetic drift and loss of adaptive potential. However the data on how gene-flow changes following habitat fragmentation is contradictory. If there is significant gene-flow between spatially isolated populations then limited conservation resources could be directed away from projects to ‘establish genetic connectivity’ and used to address other consequences of habitat fragmentation.This research focused on an endangered tree species Gomortega keule (Gomortegaceae) in a fragmented landscape in the Central Chile Biodiversity Hotspot and addressed three questions: (1) How far does pollen move between pollen donors and seed trees and what is the shape of the dispersal curve? (2) Do insect pollinators travel outside of forest patches? (3) Do small populations and single trees contribute to genetic connectivity across the landscape?Paternity analysis results show that G. keule’s insect pollinators travel outside of forest patches, over distances of 6 km, beyond the scale of population fragmentation or genetic structure. Pollen moved from small sites and single trees into large sites, as well as in the other direction, indicating these sites play a key role as functioning elements of the wider population and as stepping stones between sites. Fragmentation at the scale investigated has not led to genetic isolation, thus genetic connectivity per se is not a conservation priority. Other consequences of land-use change, specifically continuing habitat loss and population reduction, still threaten the survival of the species.     

Ecological and genetic measurements of dispersal in a threatened dragonfly

Leucorrhinia caudalis is a rare dragonfly, threatened throughout its European distribution. The species was formerly widespread in the Swiss lowlands, but only a single population remained in the 1980s. However, a spread has recently been observed, with additional ponds being colonised, sometimes at considerable distance. Despite this evidence of recent long-distance dispersal, it is unknown whether L. caudalis regularly moves among ponds or whether this is a rather rare event. A combination of an ecological mark-resight and a population genetic study was applied to investigate contemporary dispersal and the genetic footprint of the recent population history of L. caudalis in Switzerland. DNA for genetic microsatellite analysis was extracted from exuviae. The mark-resight study and the genetic analysis gave congruent results. They showed that L. caudalis is mostly a sedentary species, with only a few contemporary dispersal events over distances up to 5 km being observed. The genetic analysis was in agreement with the recent population history of the Swiss populations. The oldest and largest population showed large genetic diversity and acted as source population for the recent spread of L. caudalis in Switzerland. Recurrent gene flow among this source population and close populations caused substantial local genetic variation in the latter, as well as low population differentiation. The two recently founded distant populations (?30 km distance) were genetically less diverse and highly differentiated. These distant populations and another recently colonised population also expressed signatures of genetic bottlenecks.     

Genetic consequences of animal translocations: A case study using the field cricket, Gryllus campestris L.

Animal relocations have become a common tool in nature conservation, but the genetic consequences of such projects have rarely been studied in insects. As both natural and artificial formation of new populations may lead to genetic drift (founder effect), decreased genetic diversity and increased rates of inbreeding, genetic analyses can provide valuable information to evaluate the success of a relocation project. The field cricket (Gryllus campestris) has been subjected to reintroduction and translocation projects in England and northern Germany. Here, we present a microsatellite study on the population genetics of one recently established population of this species in comparison with several older populations and some recently colonized sites. Our results show that the translocation did not result in a significant loss of genetic diversity, when compared to source and other natural populations suggesting that translocation of a high number of nymphs from different subpopulations may be a suitable method to decrease the loss of genetic diversity and reduce the risk of inbreeding. Furthermore, the translocation had no negative effect on the source population, which reached a new maximum population size in 2006. An assignment test showed that individuals from the translocated population (F4 generation) were still assigned to the source populations, whereas two young subpopulations that originated by natural colonization from the central population about ten years ago already formed separate genetic clusters. As the strong fragmentation of G. campestris populations in northern Germany hampers natural colonization of newly created potential habitats, translocation projects seem to be an appropriate method to preserve this species.     

Genetic diversity of core and peripheral Sitka spruce (Picea sitchensis (Bong.) Carr) populations: implications for conservation of widespread species

This study investigated levels of genetic diversity and population differentiation among Sitka spruce (Picea sitchensis) populations classified as core or peripheral based on ecological niche, and continuous or disjunct based on species distribution. Large numbers of trees (N = 200) were sampled from each of eight populations to evaluate the distribution of rare as well as common alleles across the species range. Codominant alleles for eight sequence-tagged site loci were classified based on frequency and geographic distribution in order to develop appropriate sampling strategies to target specific classes of alleles. An important finding of this study is the similarity in genetic diversity as measured by expected heterozygosity between core populations (mean H_E = 0.58) and peripheral populations (mean H_E = 0.56). However, there was significant inbreeding in peripheral (F_IS = 0.17) but not in core (F_IS = 0.03) populations. Large differences in gene flow estimates were observed between core (Nm = 9.0) and peripheral populations (Nm = 3.5). Irrespective of population classification, over 75% of the alleles were common and widespread. Only one allele was classified as rare and localized, and this allele was limited to one core, disjunct and two peripheral, disjunct populations. There was stronger evidence of past bottlenecks in peripheral, disjunct populations than in core, continuous populations. Results are used to suggest sampling strategies for capture of maximum level of genetic diversity and conservation of rare alleles. The conservation of peripheral, particularly disjunct, populations as well as populations in putative glacial refugia may present the best opportunity for conserving rare alleles.     

Does reduced MHC diversity decrease viability of vertebrate populations?

Loss of genetic variation may render populations more vulnerable to pathogens due to inbreeding depression and depletion of variation in genes responsible for immunity against parasites. Here we review the evidence for the significance of variation in genes of the Major Histocompatibility Complex (MHC) for conservation efforts. MHC molecules present pathogen-derived antigens to the effector cells of the immune system and thus trigger the adaptive immune response. Some MHC genes are the most variable functional genes in the vertebrate genome. Their variation is clearly of adaptive significance and there is considerable evidence that its maintenance is mainly due to balancing selection imposed by pathogens. However, while the evidence for selection shaping MHC variation on the historical timescale is compelling, a correlation between levels of MHC variation and variation at neutral loci is often observed, indicating that on a shorter timescale drift also substantially affects MHC, leading to depletion of MHC diversity. The evidence that the loss of MHC variation negatively affects population survival is so far equivocal and difficult to separate from effects of general inbreeding. Some species with depleted MHC variation seem to be particularly susceptible to infection, but other species thrive and expand following severe bottlenecks that have drastically limited their MHC variation. However, while the latter demonstrate that MHC variation is not always critical for population survival, these species may in fact represent rare examples of survival despite of the loss of MHC variation. There is clearly a compelling need for data that would disclose the possible consequences of MHC diversity for population viability. In particular, we need more data on the impact of MHC allelic richness on the abundance of parasites or prevalence of disease in populations, while controlling for the role of general inbreeding. Before such evidence accumulates, captive breeding programs and other conservation measures aimed at inbreeding avoidance should be favoured over those protecting only MHC variation, especially since inbreeding avoidance programs would usually conserve both types of genetic diversity simultaneously.     

Genetic consequences of using seed mixtures in restoration: A case study of a wetland plant Lychnis flos-cuculi

Sowing with seed mixtures is a common practice in restoring species-rich communities in areas with impoverished species pools. The potential genetic consequences of using these mixtures, however, are poorly understood and often not considered in practical restoration. We investigated genetic diversity, inbreeding and genetic structure of samples collected from 26 populations of the common wetland plant species Lychnis flos-cuculi in an agricultural region in Switzerland. Some of these populations were natural, while others had been sown several years ago. This enabled us to compare the genetic composition of populations of indigenous origin with those originating from commercially produced seed mixtures. Gene diversity and allelic richness were similar in natural and sown populations. In contrast, inbreeding coefficients were three times higher in sown than in natural populations. The sown populations were genetically distinct from the native populations. We distinguished two homogeneous gene pools that presumably originated from different source populations used to produce seed mixtures. The use of commercially produced seeds may alter the genetic diversity and structure of plant populations. The observed higher inbreeding coefficients of sown populations could lead to reduced population viability. To restore genetically diverse populations, the seeds for further propagation should be collected from numerous individuals in large and non-isolated populations nearby restored sites. Ex situ stocks for the production of commercial seed mixtures should only be propagated for a few generations to avoid negative effects such as inbreeding or loss of local adaptation.     

The role of genetic mechanisms of sex determination in the survival of small populations of Silene littorea: A reintroduction experiment

Loss of genetic variation in populations may have other effects than inbreeding depression and loss of adaptive potential. In the case of the numerous gynodioecious plant species having cytonuclear systems of sex determination with dominant nuclear restorers of the male function, reduced genetic variation and increased inbreeding would increase the proportion of non-restorer recessive genes found in homozygosity, and therefore that of female plants producing pistillate flowers. This could have opposite effects on the extinction risk of the population. Female plants produce no pollen and may cause pollen limitation, but at the same time they may reduce average homozygosity and inbreeding depression because they are forced outcrossers. We observed that inbreeding indeed increased the frequency of female plants and pistillate flowers in the population, and that this effect was accompanied by reductions in population recruitment independent of inbreeding depression and likely due to pollen limitation. These results suggest that dominant nuclear restorers of pollen production speed up the extinction of small populations of Silene littorea, and that sex determination mechanisms might be an important factor to consider in the conservation of many plant species.     

Can landscape and species characteristics predict primate presence in forest fragments in the Brazilian Amazon?

Habitat loss and fragmentation are global conservation concerns, but animal species do not respond to these threats in the same manner. At the Biological Dynamics of Forest Fragments Project (BDFFP), located 80 km north of Manaus, Amazonas, Brazil, the distribution and persistence of six native primate species differ among fragments that were isolated in 1980s. We identified both landscape and species characteristics predicting the presence of primates in these forest fragments. Fragment size positively and distance to nearest forested area negatively predicted primate species richness in the fragments; however, these relationships were not straightforward because these two variables were correlated. The proportion of fruit in a species’ diet was the most important factor predicting its presence in the forest fragments, with species relying primarily on frugivory faring poorly. Home range size was the second-best predictor of a species’ presence; however, some species with large home ranges were present in the 10-ha forest fragments. The extent to which the individual primate species traveled in and out of the fragments varied, suggesting that further research is necessary to determine the primary factors that lead to the animals’ use of the matrix. We conclude that in addition to conserving large tracts of habitat, reducing the isolation of the forest fragments through the creation of forest corridors and through the presence of additional forest fragments within the agricultural matrix may increase animal movement across the landscape. Such changes to the matrix may be critical for those species that do not readily traverse non-forested areas.     

Integrating demographic and genetic approaches in plant conservation

We summarize the problems that populations of formerly common plants may encounter when habitat fragmentation isolates them and reduces population size. Genetic erosion, inbreeding depression, Allee-effects on reproductive success, catastrophes and environmental stochasticity are illustrated with studies on species that have recently become rare in The Netherlands due to habitat fragmentation. These clearly indicate that population viability is negatively affected. We also show that in the recent literature (since 1980), most studies on the conservation of rare plants have addressed population genetic structure and relationships between genetic variation and population size. Though important, these studies are not suitable for assessing the importance of genetics for population viability. In turn, demographic studies can detect changes in vital rates in small populations, but cannot reveal underlying genetic causes. Fitness and demographic studies are also well-represented in the literature, but remarkably few studies have attempted to integrate empirical demographic and genetic studies. We discuss two approaches to fill this very important lacuna in our knowledge. One of these constructs matrix-projection models on the basis of demographic censuses of—if possible—large and viable populations, and combines these with the results of experiments to determine inbreeding effects on demographic transitions and, subsequently, population growth and extinction. The other approach is to demographically monitor experimentally created small and large populations with low and high genetic variation and measure their actual growth rates and probabilities of extinction. We conclude that demography and demographic-genetic experiments should play a central role in plant conservation genetics.     

AFLP fingerprinting of Anchusa (Boraginaceae) in the Corso-Sardinian system: Genetic diversity, population differentiation and conservation priorities in an insular endemic group threatened with extinction

Although several plants endemic to Corsica and Sardinia are included in various redlists, no attempts have been made to analyse their genetic diversity with molecular techniques. Genus Anchusa occurs with seven taxa in either mountain or coastal habitats of the two islands, but the very restricted range and low population size pose these endemisms in a very precarious conservation status. Highly variable markers (AFLP) were therefore used to analyse the patterns and levels of genetic diversity in a sample of 11 populations from the entire range of the group.Results indicate the separation between a mountain genic pool including Anchusa formosa, Anchusa capellii and Anchusa montelinasana, and four groups of coastal accessions. In spite of small size, mountain taxa show low interpopulation differentiation (F_st = 0.02) and relatively high intrapopulation genetic variation (0.365), while coastal accessions showed on average a stronger differentiation (mean F_st = 0.20) and a lower diversity (0.281), possibly due to higher rates of inbreeding. The particularly low levels of variation found in A. sardoa, A. littorea and A. crispa ssp. maritima from the Coghinas bay are likely due to a historical decrease of populations and to bottleneck events caused by loss of habitat and natural stochastic factors on sand dune ecosystems. While habitat maintenance and regulation of grazing by domestic herbivores should be sufficient to ensure the persistence of the mountain endemics, additional actions of in situ and ex situ conservation are needed for the critically endangered coastal species A. sardoa and A. littorea. A. crispa showed a relatively high variation, especially on Corsica. No correlation between population size and genetic variation was found in the latter species, highlighting the importance of the small patches for its conservation. Also, the genetic separation between subspecies crispa and maritima stresses the need of keeping them distinct in redlists and conservation actions on Sardinia.     

Genetic diversity and local population structure of fragmented populations of Trillium camschatcense (Trilliaceae)

Trillium camschatcense, a long-lived common woodland herb, has been experiencing intensive habitat fragmentation over the last century in eastern Hokkaido, Japan. We examined the genetic diversity and population genetic structure of 12 fragmented populations with different population sizes using allozyme electrophoresis. The percentage of polymorphic loci and mean number of alleles per locus were positively related to population size, probably due to the stochastic loss of rare alleles (frequency of q<0.1) in small populations. Populations with 350 flowering plants or fewer had lost almost all of their rare alleles. While the heterozygosity and inbreeding coefficient were not related to population size, some small populations showed relatively high inbreeding coefficients. In spite of the low genetic differentiation among overall populations (F_ST=0.130), local population structuring was recognized between the two geographically discontinuous population groups. Within groups, sufficient historical gene flow was inferred, whereas a low dispersal ability of this species and geographical separation could produce apparent differentiation between groups.     

MtDNA genetic diversity and population history of a dwindling raptorial bird, the red kite (Milvus milvus)

The red kite (Milvus milvus) occurs in a relatively small area in the southwestern Palearctic region, with population strongholds in Central Europe. Following strong human persecutions at the beginning of the 20th century, populations have receded, particularly in peripheral areas and islands. In order to describe and compare levels of genetic diversity and phylogeographic patterns throughout its entire distribution in Europe, sequence variation of a 357 bps part of the mitochondrial DNA control region was assessed in eight populations and 105 individuals. Overall, results indicate that population declines have affected red kite mtDNA variation. We found low levels of genetic diversity (values of nucleotide diversity ranging from 0 in Majorca island to 0.0062 in Central Europe), with only 10 distinct haplotypes, separated by low levels of genetic divergence (mean sequence divergence = 0.75%). Highest haplotype and nucleotide diversities match with demographic expectations, and were found in Central European and Central Spanish samples, where present strongholds occur, and lowest values in the declining southern Spanish and insular samples. Φst estimates indicated moderate gene flow between populations. Phylogeographic patterns and mismatch distributions analyses suggest central European regions may have been colonized from southern glacial refugia (in the Italian or Iberian peninsulas). Interspecific phylogenetic comparisons and divergence date estimates indicated the genetic split between the red kite and its closely related species, the black kite (Milvus migrans), might be relatively recent. The low level of genetic variation found in the red kite mitochondrial control region, compared to the black kite, is likely the result of relatively recent divergence (associated with founder events), successive bottlenecks and small population sizes. As there are several ongoing projects aimed at reinforcing populations in countries such as the United Kingdom, Italy or Spain, our results may prove useful for the genetic management of the species.     

Genetic diversity and differentiation in Chinese sour cherry <Emphasis Type="Italic">Prunus pseudocerasus</Emphasis> Lindl., and its implications for conservation

In this study, the genetic diversity and differentiation of 10 natural Prunus pseudocerasus Lindl. populations were investigated using inter-simple sequence repeat (ISSR) markers. Totally, 18 selected primers generated 150 loci, with an average of 8.33 bands per primer. The results showed that the percentage of polymorphic bands (PPB) was pretty low at the population level (PPB = 1.13–32%), but relatively high at the species level (PPB = 84%). Besides, a high level of genetic differentiation among populations was detected based on the gene differentiation coefficient (G _ST = 0.7118) and the hierarchical analysis of molecular variance (AMOVA) (Φ _ST = 64.53%, P < 0.001), in line with the low inter-population gene flow (N _m = 0.2025). Moreover, Mantel test revealed a significant correlation between genetic and geographic distances among the populations (r = 0.5272, P < 0.005). The high level of intraspecific genetic diversity was probably related with its life history traits, while its small population size and the resultant high levels of genetic drift and inbreeding might explain the low genetic diversity within populations. The relatively high inter-population genetic differentiation was largely attributed to its small population size, habitat fragmentation, the mode of pollen and seed dispersal, and geographic isolation. Based on the present study, conservation strategies were proposed to preserve this valuable natural germplasm resource.     

Relationship between reservoir size and genetic differentiation of the stream caddisfly Stenopsyche marmorata

Reservoirs have the potential to block the gene flow of stream macroinvertebrates along a channel, which takes place via larval drift and adult flight, resulting in genetic differentiation above and below the reservoirs. Gene flow across the reservoirs may be strongly obstructed if the area of standing water is larger. Using random amplified polymorphic DNA markers, we investigated the genetic structure of Stenopsyche marmorata (Stenopsychidae: Trichoptera) populations found above and below the reservoirs, and the reference stream of six reservoirs with small to large water surface area ranging from 0.12 km² to 6.00 km². As a result, the two largest reservoirs with a standing water area larger than 3.27 km² showed significant differences in pairwise θ between fragmented and reference streams, whereas the other four reservoirs with a standing water area smaller than 1.64 km² showed insignificant differences. The genetic differentiations in the two largest reservoirs did not result in the reduction of genetic diversities in the fragments. Based on the significant correlation between relative population size and mean expected heterozygosity, we concluded that local genetic diversities were constrained in smaller populations due to the effect of genetic drift.     

Insular pest control within a metapopulation context

Introduced pests threaten many species and their control is generally beneficial for conservation, particularly on islands where complete eradication is possible. Unfortunately on ‘nearshore’ islands neighbouring source populations exist and unaided reinvasion is likely. Pest control programmes at these sites thus require a metapopulation context to adequately manage movements between source and sink populations. We investigated the ecology of introduced ship rats (Rattus rattus) on a nearshore island, and gene flow with adjacent mainland populations, in order to understand the metapopulation dynamics and relative levels of pest control required within the landscape. We sampled the entire population by trapping (n = 30), achieving eradication, and found a low rat density (3.2 ha⁻¹) indicative of a sink population. Seed and other plant material constituted the major dietary component of rats. Despite its proximity to mainland source populations, the island population was genetically distinct with reduced allelic diversity caused by a recent reinvasion founder effect. Genetic analyses also detected recent migrants between the populations. In contrast, two mainland populations separated by a similar distance displayed complete genetic mixing. The small water gap therefore provides a sufficient barrier to lower the migration rate to the island and delay reinvasion, which nonetheless eventually happens. In order to maintain nearshore islands pest-free, conservation management will require a metapopulation approach simultaneously focusing on both island and source population pest control.     

Effects of flood events on the genetic structure of riparian populations of the grassland plant Origanum vulgare

River regulation results in the disconnection and increased fragmentation of habitats in the river corridor. In this study, we investigated the within-population genetic variability and among-population genetic differentiation of 21 populations of Origanum vulgare along the River Meuse, using dominant AFLP markers, in order to asses the restoration potential of this species in the context of current river restoration efforts. The average observed within-population genetic diversity was high and suggests that river regulation and associated fragmentation of the populations have not strongly affected genetic diversity. The genetic differentiation between populations was high (Φ_ST = 0.24) and can be explained by founder effects, rather than by genetic drift in isolated populations. We also detected a pronounced hierarchic spatio-temporal structure in genetic variation. This structure can be related to the irregular patterns in the flow regime of the River Meuse. Large floods are the major vector of genetic structure, but geographic upstream proximity, probably mediated by small floods, also has an important effect on genetic structure. Three distinct groups of populations were observed, two of which could be related to the extreme flood events of the mid-nineties of last century. Assignment tests revealed occasional long-distance seed dispersal with extreme flood events and local colonisation with more regular floods. Our study species optimally took benefit of the opportunities offered by the river restoration programme, with a strong colonisation after floods, and illustrates the need for maintaining river dynamics to conserve and restore genetic diversity.     

Rare species

An operational definition of rare species might include the specification that it either occurs in widely separated, small sub-populations so that interbreeding between sub-populations is seriously reduced, or is restricted to a single population. It has usually been assumed that depauperization of habitat and reduction of genetic material have occurred in rare species, but recent studies of electrophoretically identified genetic polymorphisms suggest that some small populations and some inbreeding populations may retain considerable heterogeneity. Because different populations of a species tend to differ in genetic composition, one would expect the number of sub-populations to be more important for the population's security than the total population size. Specialization of an isolated inbreeding population to a restricted homogeneous habitat under pressure of competition should have serious ecological consequences. This reasoning suggests several conclusions. The protection of an isolated, reduced population in its present state may encourage further specialization and conservatism. In rehabilitating a relict population a first step might be to encourage it to break up into largely, but not completely, independent sub-populations. In a breeding programme, variability should be deliberately promoted as well as quick turnover between the breeding population and the wild. Very high mortality of released individuals must be expected, because it is the rule in the wild even in a rapidly increasing population.