The Theory of Island Biogeography on the Hawaiki Archipelago

<p>This thesis addresses MacArthur and Wilson‟s Theory of Island Biogeography (1967) on a set of islands around the north-east coast of the North Island of New Zealand. The flora species lists from these islands were obtained from both published and unpublished island surveys whilst Geographical Information Systems (GIS) techniques were utilised in order to calculate the physical geography of islands. These islands were an ideal study site for such research because they display natural gradients in both physical geography as well as native and exotic species richness. The literature on the Theory of Island Biogeography has yet to comprehensively understand the differences between the patterns of exotic richness and native richness. Furthermore, the importance of studies on exotics species is increasingly relevant given the negative effect they have had on native communities worldwide. The results of my research illustrated that there were similar species-area and species-isolation relationships between exotic and native species. These two relationships were also consistent with what is expected under classical island biogeography principles. Interestingly however, I found that distance from the mainland had a stronger negative effect on exotics species. There were a significantly lower proportion of exotics with increasing isolation. This result has applicable outcomes for conservation management on the Hawaiki archipelago. I suggested that weeding effort focus on larger islands and in particular the islands closer to the mainland. Globally, the biogeographical patterns of exotic species are still poorly examined. With insights from this study and other similar research the Theory of Island Biogeography may be an informative approach to dealing with the ominous threat of exotic species.</p>

The Theory of Island Biogeography on the Hawaiki Archipelago

<p>This thesis addresses MacArthur and Wilson‟s Theory of Island Biogeography (1967) on a set of islands around the north-east coast of the North Island of New Zealand. The flora species lists from these islands were obtained from both published and unpublished island surveys whilst Geographical Information Systems (GIS) techniques were utilised in order to calculate the physical geography of islands. These islands were an ideal study site for such research because they display natural gradients in both physical geography as well as native and exotic species richness. The literature on the Theory of Island Biogeography has yet to comprehensively understand the differences between the patterns of exotic richness and native richness. Furthermore, the importance of studies on exotics species is increasingly relevant given the negative effect they have had on native communities worldwide. The results of my research illustrated that there were similar species-area and species-isolation relationships between exotic and native species. These two relationships were also consistent with what is expected under classical island biogeography principles. Interestingly however, I found that distance from the mainland had a stronger negative effect on exotics species. There were a significantly lower proportion of exotics with increasing isolation. This result has applicable outcomes for conservation management on the Hawaiki archipelago. I suggested that weeding effort focus on larger islands and in particular the islands closer to the mainland. Globally, the biogeographical patterns of exotic species are still poorly examined. With insights from this study and other similar research the Theory of Island Biogeography may be an informative approach to dealing with the ominous threat of exotic species.</p>

The Dynamic Hypercube as a Niche Community Model

Different models of community dynamics, such as the MacArthur–Wilson theory of island biogeography and Hubbell’s neutral theory, have given us useful insights into the workings of ecological communities. Here, we develop the niche-hypervolume concept of the community into a powerful model of community dynamics. We describe the community’s size through the volume of the hypercube and the dynamics of the populations in it through the fluctuations of the axes of the niche hypercube on different timescales. While the community’s size remains constant, the relative volumes of the niches within it change continuously, thus allowing the populations of different species to rise and fall in a zero-sum fashion. This dynamic hypercube model reproduces several key patterns in communities: lognormal species abundance distributions, 1/f-noise population abundance, multiscale patterns of extinction debt and logarithmic species-time curves. It also provides a powerful framework to explore significant ideas in ecology, such as the drift of ecological communities into evolutionary time.

Conservation in Protected Areas

Chapter 11 focuses on protected areas. It considers how the principles developed in earlier chapters inform protected area design—especially their size, shape, and expected duration—and management. It covers the ecological principles involved (threat, distinctness, and representativeness), and their connection to the theory of island biogeography. It then discusses how these are modified by economic principles requiring that the benefits of protection need to offset the opportunities forgone by committing resources to the acquisition of the necessary rights, the additional cost of conservation effort, and the net costs to those impacted by the change in rights. It is shown how evaluation of the trade-offs involved makes it possible to identify the optimal size of individual protected areas, or the optimal structure of a network of protected areas.

Classics revisited: “Mammals on mountaintops: nonequilibrium insular biology” (The American Naturalist, 105: 467–478, 1971), by James H. Brown

James H. Brown’s “Mammals on mountaintops: nonequilibrium insular biogeography,” published in 1971 in The American Naturalist, documented distributional patterns of small mammal species in the mountaintop islands of the Great Basin, USA. Distributional patterns suggested that this island-like system was not in equilibrium and represented some of the first evidence contradicting the seminal Theory of Island Biogeography. Brown’s findings suggested that ecological and historical mechanisms were integral to community assembly and maintenance in island-like systems, broadening the focus of research related to biogeographical patterns in islands. The work further highlighted the importance of species traits on distributional patterns. Here, I review the paper and its contributions.

Marine macroinvertebrate species-area relationships, assemblage structure and their environmental drivers on submarine banks

Modern extensions of the theory of island biogeography (TIB) posit that the slope of the species-area relationship (SAR) reflects the insularity of ecological communities and is strongly influenced by species’ motility. We explore the relative insularity of crustacean, echinoderm and mollusk/Cirripedia assemblages in terms of both alpha diversity (species richness) and assemblage structure (relative biomass of species). These taxa/groups differ in adult motility and larval dispersal capacity. The habitats of interest were 10 offshore banks on the Scotian Shelf, northwest Atlantic Ocean, a region dominated by the NE- to SW-flowing Nova Scotia Current (NSC). Banks in the NE tended to be larger, more heterogeneous, cooler, less saline, more retentive and more productive (higher chlorophyll a) than those in the SW. Only mollusks/Cirripedia, the least motile and dispersive group, had a significant SAR slope, supporting TIB. For crustaceans and echinoderms, temperature/salinity properties and habitat heterogeneity, respectively, were important predictors of alpha diversity. Inter-bank variation in crustacean assemblage structure was accounted for largely by bank location relative to the NSC; the leading variables accounting for echinoderm and mollusk/Cirripedia assemblage structure were retention time and mean annual chlorophyll concentration, respectively. Along the NE to SW axis of the NSC, there was a substantial loss of species (7 crustacean, 9 echinoderm and 13 mollusk/Cirripedia species) and decreases in the biomass of common cold-water species. A complex interplay of species motility/dispersal capacity, local oceanography and habitat properties determine the extent to which (1) TIB applies to submarine macroinvertebrate assemblages and (2) upstream and downstream assemblages are interconnected.

Island biogeography on a micro-scale: Larger anammox granules not only harbor higher species diversity but also support more functional diversity

Background: According to the theory of island biogeography, there is a strong relationship between the species diversity and the isolated area. However, it is unclear whether the ecological distribution of microorganisms follows this island biogeography pattern at micro-scale. Here, we use microbial granules harvested from a partial nitritation and anammox (PN/A) system as a model to test if the microbial and functional diversity follow the island biogeography. We collected and divided these granules into five discrete size-fractions (<0.2, 0.2–0.5, 0.5–0.8, 0.8–1.0 and >1.0 mm).Results: By comparing the composition and functional attribute of five pools of the size-fractionated granules by 16S rRNA gene amplicon, metagenomic and metatranscriptomic sequencing, larger granules were shown not only to harbor higher microbial diversity, but also to support more diverse functions than smaller granules. De novo co-assembly and binning of metagenomic reads yielded 22 near-complete genomes of dominant microorganisms, which allowed us to infer an ecological model of the microbial ecosystem in anammox-based granules. This genome-based ecological model indicates that nitrifying organisms in smaller granules feed nitrite to anammox bacteria in larger granules.Conclusion: Our findings substantiate that microbial communities in PN/A granules follow a species-volume relationship, suggesting the generality of the theory of island biogeography on microscopic scale.

Marine subsidies mediate patterns in avian island biogeography

The classical theory of island biogeography , which predicts species richness using island area and isolation, has been expanded to include contributions from marine subsidies, i.e. subsidized island biogeography (SIB) theory . We tested the effects of marine subsidies on species diversity and population density on productive temperate islands, evaluating SIB predictions previously untested at comparable scales and subsidy levels. We found that the diversity of terrestrial breeding bird communities on 91 small islands (approx. 0.0001–3 km 2 ) along the Central Coast of British Columbia, Canada were correlated most strongly with island area, but also with marine subsidies. Species richness increased and population density decreased with island area, but isolation had no measurable influence. Species richness was negatively correlated with marine subsidy, measured as forest-edge soil δ 15 N. Density, however, was higher on islands with higher marine subsidy, and a negative interaction between area and subsidy indicates that this effect is stronger on smaller islands, offering some support for SIB. Our study emphasizes how subsidies from the sea can shape diversity patterns on islands and can even exceed the importance of isolation in determining species richness and densities of terrestrial biota.

Megafauna decline have reduced pathogen dispersal which may have increased emergent infectious diseases

The Late Quaternary extinctions of megafauna (defined as animal species >44.5 kg) reduced the dispersal of seeds and nutrients, and likely also microbes and parasites. Here we use body-mass based scaling and range maps for extinct and extant mammal species to show that these extinctions led to an almost seven-fold reduction in the movement of gut-transported microbes, such as Escherichia coli (3.3 km2/day to 0.5 km2/day). Similarly, the extinctions led to a seven-fold reduction in the mean home ranges of vector-borne pathogens (7.8 km2 to 1.1 km2). To understand the impact of this, we created an individual-based model where an order of magnitude decrease in home range increased maximum aggregated microbial mutations 4-fold after 20,000 years. We hypothesize that pathogen speciation and hence endemism increased with isolation, as global dispersal distances decreased through a mechanism similar to the theory of island biogeography. To investigate if such an effect could be found, we analysed where 145 zoonotic diseases have emerged in human populations and found quantitative estimates of reduced dispersal of ectoparasites and fecal pathogens significantly improved our ability to predict the locations of outbreaks (increasing variance explained by 8%). There are limitations to this analysis which we discuss in detail, but if further studies support these results, they broadly suggest that reduced pathogen dispersal following megafauna extinctions may have increased the emergence of zoonotic pathogens moving into human populations.