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 current paper synthesizes theory and data from the field of life history (LH) evolution to advance a new developmental theory of variation in human LH strategies. The theory posits that clusters of correlated LH traits (e.g., timing of puberty, age at sexual debut and first birth, parental investment strategies) lie on a slow-to-fast continuum; that harshness (externally caused levels of morbidity-mortality) and unpredictability (spatial-temporal variation in harshness) are the most fundamental environmental influences on the evolution and development of LH strategies; and that these influences depend on population densities and related levels of intraspecific competition and resource scarcity, on age schedules of mortality, on the sensitivity of morbidity-mortality to the organism’s resource-allocation decisions, and on the extent to which environmental fluctuations affect individuals versus populations over short versus long timescales. These interrelated factors operate at evolutionary and developmental levels and should be distinguished because they exert distinctive effects on LH traits and are hierarchically operative in terms of primacy of influence. Although converging lines of evidence support core assumptions of the theory, many questions remain unanswered. This review demonstrates the value of applying a multilevel evolutionary-developmental approach to the analysis of a central feature of human phenotypic variation: LH strategy.

https://cals.arizona.edu/fcs/sites/cals.arizona.edu.fcs/files/HN%20Ellis%20et%20al%202009.pdf

Fundamental Dimensions of Environmental Risk : The Impact of Harsh versus Unpredictable Environments on the Evolution and Development of Life History Strategies.

A review of the literature shows that in nearly all cases tropical rain forest fragmentation has led to a local loss of species. Isolated fragments suffer reductions in species richness with time after excision from continuous forest, and small fragments often have fewer species recorded for the same effort of observation than large fragments or areas of continuous forest. Birds have been the most frequently studied taxonomic group with respect to the effects of tropical forest fragmentation. The mechanisms of fragmentation-related extinction include the deleterious effects of human disturbance during and after deforestation, the reduction of population sizes, the reduction of immigration rates, forest edge effects, changes in community structure (second- and higher-order effects) and the immigration of exotic species. The relative importance of these mechanisms remains obscure. Animals that are large, sparsely or patchily distributed, or very specialized and intolerant of the vegetation surrounding fragments, are particularly prone to local extinction. The large number of indigenous species that are very sparsely distributed and intolerant of conditions outside the forest make evergreen tropical rain forest particularly susceptible to species loss through fragmentation. Much more research is needed to study what is probably the major threat to global biodiversity.

Species loss in fragments of tropical rain forest: a review of the evidence.

We evaluated the conditions under which patch size effects are important determinants of local population density for animals living in patchy landscapes. This information was used to predict when patch size effects will be expected to occur following habitat loss and fragmentation. Using meta-analysis, we quantitatively reviewed the results of 25 published studies that tested for a relationship between patch size and population density. Patch size effects were strong for edge and interior species (negative and postive patch size effects, respectively), but negligible for generalist species that use both edge and interior habitat. We found significant differences in mean patch size effects between migratory and residential species, between herbivores and carnivores, and among taxonomic groups. We found no evidence that patch size effects were related to landscape character- istics such as the proportion of landscape covered by habitat, median patch size, or the scale at which a study was conducted. However, species in the Western Hemisphere tended to have larger absolute effect sizes, and eastern species tended to be more variable in their response. For landscapes undergoing habitat loss and fragmentation, our results predict the fol- lowing: (1) among generalist species that use both the edge and the interior of a habitat patch, the decline in population size associated with habitat destruction should be accounted for by pure habitat loss alone; (2) for interior species, the decline in population size as- sociated with habitat fragmentation per se will be greater than that predicted from pure habitat loss alone; (3) for edge species, the decline in population size will be less than that predicted by pure habitat loss alone; (4) these relative effects will not be influenced by the extent of habitat loss, but they will be affected by the pattern of habitat when large or small patches are preferentially removed; and (5) as loss and fragmentation increase within a landscape, migratory species will generally suffer less of a decline in population size than resident species.

https://www.fws.gov/southwest/es/documents/R2ES/LitCited/LPC_2012/Bender_et_al_1998.pdf

Habitat loss and population decline: a meta‐analysis of the patch size effect

1. The abundance and distribution of species tend to be linked, such that species declining in abundance often tend also to show declines in the number of sites they occupy, while species increasing in abundance tend also to be increasing in occupancy. Therefore, intraspecific abundance–occupancy relationships are commonly positive.



2. The intraspecific pattern is mirrored by more general positive interspecific abundance–occupancy relationships: widespread species tend to be abundant, and narrowly distributed species rare.



3. Here, we review recent research on these patterns based on the flora and fauna of the British Isles. We assess their generality, describe what is currently known about their structure, and summarize the results of tests of the several hypotheses proposed to explain their existence.



4. The positive form generally exhibited by abundance–occupancy relationships, intraspecific or interspecific, has consequences for several areas of applied ecology, including conservation, harvesting, biological invasions and biodiversity inventorying. These implications are discussed briefly.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2664.2000.00485.x

Abundance–occupancy relationships

Populations of rodents isolated on islands often show systematic differences in demography, reproduction, behavior, and morphology when compared to mainland populations. These differences, termed the island syndrome, include higher and more stable densities, better survival, increased body mass, and reduced aggressiveness, reproductive output, and dispersal. We synthesize information in the literature on island rodent populations and construct a conceptual model to explain the island syndrome. Population density and other manifestations of the island syndrome are predicted to increase with island isolation and to decrease with island area. The effect of isolation is direct by limiting dispersal, while the effect of area is less direct. As area increases, predators, competitors, and habitat structure increase in diversity. We suggest that the intensity or absence of density-depressing factors (primarily predation in communities comprised of only a few morphologically and trophically divergent species) is primarily responsible for the area effect and serves as a principal factor differentiating island from mainland populations of rodents. Other characteristics associated with the island syndrome may be the result of both short-term and long-term processes or responses. Short-term responses include reproductive, body size, and behavioral changes that may be phenotypic reaction norms in response to higher island densities. Thus, higher densities lead to reduced reproductive output, which then leads to greater body size. Initial behavioral differences may be owing to better survival and reduced dispersal, which result in less population turnover, greater neighbor familiarity, and less aggression. Long-term changes may be due to directional selection for reduced dispersal, increased body size in response to increased intraspecific competition, reduced reproductive output (smaller litters and delayed maturation) in response to reduced mortality schedules, and reduced aggressiveness. While the model is specific to rodent populations, the conclusions may be applicable to other systems if characteristics such as body size, vagility, and community composition are considered.

The island syndrome in rodent populations.

To determine whether the abundance of the northern deer tick, Ixodes dammini is dependent upon that of white-tailed deer, Odocoileus virginianus (Boddaert), the host most frequently parasitized by adult ticks, we compared the relative abundance of deer and of immature ticks on 13 islands in Massachusetts. Abundance of larval I. dammini attached to white-footed mice, Peromyscus leucopus (Raphinesque), correlated with density of deer pellet groups, and was greatest on islands having resident deer and least on islands with few signs of deer. This relationship did not hold in the case of nymphal ticks. Deer density may largely determine abundance of larvae by affecting success of adult engorgement and subsequent reproduction. The more diffuse distribution of nymphal ticks may, in part, be explained by the tendency of larval (but not adult) ticks to be transported between islands while feeding on birds.

Correlation between Abundance of Deer and That of the Deer Tick, Ixodes dammini (Acari: Ixodidae)

A population of white-footed mice (Peromyscus leucopus) in southeastern Massachusetts was lived-trapped monthly in five habitat types for 5 yr in order to study the demography of a habitat generalist. We identified three demographic groups (two of low density and one of high density), which differed primarily in density, adult survival, proportion of males breeding, and variability in the proportion of males. The low-density segments of this population were at times able to achieve demographic performance equivalent to the high-density segments. Several demographic variables were related linearly to microhabitat gradients derived from a principal components analysis of 24 habitat variables, but similar demographic structure was found in different habitat types. A simple model is presented that relates demography to environmental suitability in a habitat generalist. According to this model, population density, productivity, and survival increase, and numerical and demographic variability decrease, along a gradient of increasing environmental suitability. Intensity of intrinsic regulation also may increase with environmental suitability, which would contribute to population stability. We hypothesize that in habitat generalists such as Peromyscus leucopus, population numbers are regulated along a stable trajectory in areas of high suitability, but may show little or no intrinsic regulation in poorer habitats. Furthermore, demographic structure may shift as environmental conditions improve or decline in quality. This highly flexible demographic structure may enable populations of generalists to persist in poor habitats.

Demography of a Habitat Generalist, The White-Footed Mouse, in a Heterogeneous Environment.

Populations of Proechimys semispinosus (Central American spiny rat) were provisioned with fresh native fruits for 6 mo to test the hypothesis that populations of frugivorous rodents in seasonal Neotropical forests are not limited by food during the season of greatest resource abundance. Islands in the Panama Canal were used as experimental systems so that results would not be confounded by individuals commuting from the fringes of the study areas. Populations isolated on four islands were censused by monthly live-trapping and served as unmanipulated controls, while populations isolated on four additional islands were provisioned with fruit at 315.2 kg/ha and censused by similar methods. Natural fruit abundance was concurrently censused by counting numbers of fruiting trees and lianas to account for naturally available resources. Means of overall spiny rat density and density of known births were compared between treatment groups using repeated-measures analysis of covariance, with the density of fruiting trees and lianas as the covariate. Both variables showed a treatment effect, with higher-than-expected densities and densities of births within experimental populations based on natural resource abundance. Numbers of known births per adult female were compared between treatment groups by constructing a log-linear model. This model also revealed a treatment effect, with per capita production of young being higher within all experimental populations. Monthly survival rates of young and adults were compared between treatment groups by constructing separate linear models for young and adults, and no treatment effect was evident. Adult male body mass was compared among islands by analysis of variance and similarly showed no treatment effect. Results showed that these spiny rat populations were limited by food even during the period of high resource abundance, and increased densities were due to increased production and recruitment of young rather than to increased immigration or survival.

Impacts of Resource Abundance on Populations of a Tropical Forest Rodent

It is now understood that alterations in the species composition of soil organisms can lead to changes in aboveground communities. In this study, we assessed the importance of spatial scale and forest size on changes in arbuscular mycorrhizal fungal (AMF) spore communities by sampling AMF spores in soils of forested mainland and island sites in the vicinity of Gatun Lake, Republic of Panama. We encountered a total of 27 AMF species or morphospecies, with 17, 8, 1 and 1 from the genera Glomus, Acaulospora, Sclerosystis, and Scutellospora, respectively. At small scales ( 5) away than to nearby island plots (within 0.7 km). Likewise, most island plots were more similar to other island plots regardless of geographic separation. There was no decay in AMF species richness (number of species), or Shannon diversity (number of species and their spore numbers) either with decreasing forest-fragment size, or with decreasing plant species richness. Of the six most common species that composed almost 70% of the total spore volume, spores of Glomus “tsh” and G. clavisporum were more common in soils of mainland plots, while spores of Glomus “small brown” and Acaulospora mellea were more abundant in soils of island plots. None of these common AMF species showed significant associations with soil chemistry or plant diversity. We suggest that the convergence of common species found in AMF spore communities in soils of similar forest sizes was a result of forest fragmentation. Habitat-dependent convergence of AMF spore communities may result in differential survival of tree seedlings regenerating on islands versus mainland.

Gregory H. Adler

Papers

The island syndrome in rodent populations.

Correlation between Abundance of Deer and That of the Deer Tick, Ixodes dammini (Acari: Ixodidae)

Demography of a Habitat Generalist, The White-Footed Mouse, in a Heterogeneous Environment.

Impacts of Resource Abundance on Populations of a Tropical Forest Rodent

Diversity of arbuscular mycorrhizal fungi across a fragmented forest in Panama: insular spore communities differ from mainland communities.