Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

The invasion of ecosystems by exotic species is currently viewed as one of the most important sources of biodiversity loss. The largest part of this loss occurs on islands, where indigenous species have often evolved in the absence of strong competition, herbivory, parasitism or predation. As a result, introduced species thrive in those optimal insular ecosystems affecting their plant food, competitors or animal prey. As islands are characterised by a high rate of endemism, the impacted populations often correspond to local subspecies or even unique species. One of the most important taxa concerning biological invasions on islands is mammals. A small number of mammal species is responsible for most of the damage to invaded insular ecosystems: rats, cats, goats, rabbits, pigs and a few others. The effect of alien invasive species may be simple or very complex, especially since a large array of invasive species, mammals and others, can be present simultaneously and interact among themselves as well as with the indigenous species. In most cases, introduced species generally have a strong impact and they often are responsible for the impoverishment of the local flora and fauna. The best response to these effects is almost always to control the alien population, either by regularly reducing their numbers, or better still, by eradicating the population as a whole from the island. Several types of methods are currently used: physical (trapping, shooting), chemical (poisoning) and biological (e.g. directed use of diseases). Each has its own set of advantages and disadvantages, depending on the mammal species targeted. The best strategy is almost always to combine several methods. Whatever the strategy used, its long-term success is critically dependent on solid support from several different areas, including financial support, staff commitment, and public support, to name only a few. In many cases, the elimination of the alien invasive species is followed by a rapid and often spectacular recovery of the impacted local populations. However, in other cases, the removal of the alien is not sufficient for the damaged ecosystem to revert to its former state, and complementary actions, such as species re-introduction, are required. A third situation may be widespread: the sudden removal of the alien species may generate a further disequilibrium, resulting in further or greater damage to the ecosystem. Given the numerous and complex population interactions among island species, it is difficult to predict the outcome of the removal of key species, such as a top predator. This justifies careful pre-control study and preparation prior to initiating the eradication of an alien species, in order to avoid an ecological catastrophe. In addition, long-term monitoring of the post-eradication ecosystem is crucial to assess success and prevent reinvasion.

http://max2.ese.u-psud.fr/epc/conservation/PDFs/BiolReviews.pdf

Mammal invaders on islands: impact, control and control impact

Island populations are much more prone to extinction than mainland populations. The reasons for this remain controversial. If inbreeding and loss of genetic variation are involved, then genetic variation must be lower on average in island than mainland populations. Published data on levels of genetic variation for allozymes, nuclear DNA markers, mitochondrial DNA, inversions and quantitative characters in island and mainland populations were analysed. A large and highly significant majority of island populations have less allozyme genetic variation than their mainland counterparts (165 of 202 comparisons), the average reduction being 29 per cent. The magnitude of differences was related to dispersal ability. There were related differences for all the other measures. Island endemic species showed lower genetic variation than related mainland species in 34 of 38 cases. The proportionate reduction in genetic variation was significantly greater in island endemic than in nonendemic island populations in mammals and birds, but not in insects. Genetic factors cannot be discounted as a cause of higher extinction rates of island than mainland populations.

/pdf/do-island-populations-have-less-genetic-variation-than-17siuwjycj.pdf

Do island populations have less genetic variation than mainland populations

The evolutionary significance of genetic diversity of proteins in nature remains controversial despite the numerous protein studies conducted electrophoretically during the last two decades. Ironically, the discovery of extensive protein polymorphisms in nature (reviewed by Lewontin, 1974; Powell, 1975; Selander, 1976; Nevo 1978, 1983b; Hamrick et al., 1979; Nelson and Hedgecock, 1980), did not resolve the disagreement between the die ho torn ou s explanatory models of selection (e.g., Ayala, 1977; Milkman, 1978; Clarke, 1979; Wills, 1981) versus neutrality (Kimura, 1968; Kimura and Chta, 1971; Nei, 1975; and modifications in Kimura, 1979atb). The more general problem of the relative importance of the evolutionary forces interacting in genetic population differentiation at the molecular levels of proteins and DNA, i.e., mutation, migration, natural selection and genetic drift, remains now as enigmatic as ever.

The Evolutionary Significance of Genetic Diversity: Ecological, Demographic and Life History Correlates

Natural disturbances such as lava flows, landslides and glacial moraines, and human-damaged sites such as pavement, road edges and mine wastes often leave little or no soil or biological legacy. This 2003 book provided the first comprehensive summary of how plant, animal and microbial communities develop under the harsh conditions following such dramatic disturbances. The authors examine the basic principles that determine ecosystem development and apply the general rules to the urgent practical need for promoting the reclamation of damaged lands. Written for ecologists concerned with disturbance, landscape dynamics, restoration, life histories, invasions, modeling, soil formation and community or population dynamics, this book will also serve as an authoritative text for graduate students and a valuable reference for professionals involved in land management.

/pdf/primary-succession-and-ecosystem-rehabilitation-46xfnlnrj7.pdf

Primary Succession and Ecosystem Rehabilitation

Environmentally induced variation in survival and fecundity generates demographic fluctuations that affect population growth rate. However, a general pattern of the comparative influence of variation in fecundity and juvenile survival on elephant population dynamics has not been investigated at a broad scale. We evaluated the relative importance of conception, gestation, first year survival and subsequent survivorship for controlling demographic variation by exploring the relationship between past environmental conditions determined by integrated normalized difference vegetation index (INDVI) and the shape of age distributions at 17 sites across Africa. We showed that, generally, INDVI during gestation best explained anomalies in age structure. However, in areas with low mean annual rainfall, INDVI during the first year of life was critical. The results challenge Eberhardt’s paradigm for population analysis that suggests that populations respond to limited resource availability through a sequential decrease in juvenile survival, reproductive rate and adult survival. Contrastingly, elephants appear to respond first through a reduction in reproductive rate. We conclude that this discrepancy is likely due to the evolutionary significance of extremely large body size – an adaptation that increases survival rate but decreases reproductive potential. Other megaherbivores may respond similarly to resource limitation due to similarities in population dynamics. Knowing how vital rates vary with changing environmental conditions will permit better forecasts of the trajectories of megaherbivore populations.

Drivers of megaherbivore demographic fluctuations: inference from elephants

Placentation in the African Elephant (Loxodonta africana): II Morphological Changes in the Uterus and Placenta Throughout Gestation

Successional changes in rehabilitating coastal dune communities in northern KwaZulu/Natal, South Africa

An analysis of census information published for the years 1952, 1958,1960 and 1970 and that obtained during this study in 1977, indicates that both the breeding bull and cow components of this population fluctuated in numbers during the past 25 years. In spite of these fluctuations, the general trend for the cow component was to increase at a rate of 1,4% per year, while the bull component decreased at a rate of 1,9% per year. An analysis based on subdivisions of the study area into distinct regions indicated that the range of fluctuation increased as mean density increased. The population is regarded as a stable fluctuating population and the influence of environmental and social factors on the observed population trends is discussed.

Fluctuations in the Population of Southern Elephant Seals Mirounga Leonina at Kerguelen Island

The aim of this study was to examine the progestin content and biosynthetic potential of the corpus luteum of the African elephant (Loxodonta africana). Luteal tissue was collected from nonpregnant and early, mid- and late pregnant elephants (n = 2 per group) shot in the Kruger National Park. Pieces of individual corpora lutea (2\p=n-\3per animal; 23 in total) were stored directly in ethanol before hormone analysis. Matching tissue pieces were incubated for 2 h with [3H]pregnenolone (2 \m=x\105 c.p.m.), after which tissue plus medium were also stored in ethanol. Progesterone and 17\g=a\-hydroxyprogesteroneimmunoreactivity in tissue extracts were determined by enzymeimmunoassay and radioimmunoassay, respectively, before and after reverse phase HPLC. Progesterone immunoreactivity predominated over that of 17\g=a\-hydroxyprogesteronein all corpora lutea examined but concentrations of both hormones were very low (73\p=n-\374ng g\m=-\1 and 3\p=n-\93 ng g\m=-\1,respectively after HPLC). There were no obvious differences in hormone concentrations in corpora lutea from animals at different reproductive stages. Progesterone and 17\g=a\-hydroxyprogesterone immunoreactivity assayed before HPLC was 10\p=n-\30times higher than that measured after chromatographic separation. HPLC consistently revealed two large immunoreactive peaks associated with relatively nonpolar compounds, which together accounted for most (at least 75%) of all progesterone immunoreactivity measured. Large amounts of radioactivity with the same retention times as these peaks were also detected after HPLC in samples incubated with [3H]pregnenolone. Analysis of conversion products from four corpus luteum incubations indicated that between 52% and 84% of [3H]pregnenolone had been converted; 19\p=n-\33%was accounted for by progesterone, and 12\p=n-\50%by the two substances represented by the unidentified peaks. Subsequent GCMS analysis identified the two immunoreactive peaks as 5\g=a\-pregnane-3\g=a\-ol-20-one and 5\g=a\-pregnane-3,20-dione (5\g=a\-dihydroprogesterone). These results indicate that the major progestins contained within and biosynthesized by corpora lutea of African elephants are 5\g=a\-reduced metabolites, and that progesterone and 17\g=a\-hydroxyprogesterone are quantitatively of minor importance.

/pdf/progestin-content-and-biosynthetic-potential-of-the-corpus-2jlxvns8p3.pdf

R. J. van Aarde

Papers

Drivers of megaherbivore demographic fluctuations: inference from elephants

Placentation in the African Elephant (Loxodonta africana): II Morphological Changes in the Uterus and Placenta Throughout Gestation

Successional changes in rehabilitating coastal dune communities in northern KwaZulu/Natal, South Africa

Fluctuations in the Population of Southern Elephant Seals Mirounga Leonina at Kerguelen Island

Progestin content and biosynthetic potential of the corpus luteum of the African elephant (Loxodonta africana)