Maintenance of biodiversity on islands

MacArthur and Wilson's theory of island biogeography predicts that island species richness should increase with island area. This prediction generally holds among large islands, but among small islands species richness often varies independently of island area, producing the so-called ‘small-island effect’ and an overall biphasic species–area relationship (SAR). Here, we develop a unified theory that explains the biphasic island SAR. Our theory's key postulate is that as island area increases, the total number of immigrants increases faster than niche diversity. A parsimonious mechanistic model approximating these processes reproduces a biphasic SAR and provides excellent fits to 100 archipelago datasets. In the light of our theory, the biphasic island SAR can be interpreted as arising from a transition from a niche-structured regime on small islands to a colonization–extinction balance regime on large islands. The first regime is characteristic of classic deterministic niche theories; the second regime is characteristic of stochastic theories including the theory of island biogeography and neutral theory. The data furthermore confirm our theory's key prediction that the transition between the two SAR regimes should occur at smaller areas, where immigration is stronger (i.e. for taxa that are better dispersers and for archipelagos that are less isolated).

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Boreal ground-beetle (Coleoptera: Carabidae) assemblages of the mainland and islands in Lac la Ronge, Saskatchewan, Canada

The Canadian Entomologist ◽

10.4039/tce.2017.12 ◽

2017 ◽

Vol 149 (4) ◽

pp. 491-503 ◽

Cited By ~ 2

Author(s):

Aaron J. Bell ◽

Iain D. Phillips ◽

Scott E. Nielsen ◽

John R. Spence

Keyword(s):

Species Richness ◽

Island Biogeography ◽

Passive Sampling ◽

Unit Area ◽

Ground Beetle ◽

Small Islands ◽

Island Size ◽

Extinction Rates ◽

Theory Of Island Biogeography ◽

Species Area

AbstractWe tested the applicability of the “passive sampling” hypothesis and theory of island biogeography (TIB) for explaining the diversity of forest-dwelling carabid assemblages (Carabidae: Coleoptera) on 30 forested islands (0.2–980.7 ha) in Lac la Ronge and the adjacent mainland in Saskatchewan, Canada. Species richness per unit area increased with distance to mainland with diversity being highest on the most isolated islands. We detected neither a positive species-area relationship, nor significant differences in species richness among island size classes, or between islands and the mainland. Nonetheless, carabid assemblages distinctly differed on islands <1 ha in area and gradually approached the structure of mainland assemblages as island area increased. Small islands were characterised by abundant populations of small-bodied, winged species and few if any large-bodied, flightless species like Carabus taedatus Fabricius. Our findings suggest that neither the “passive sampling” hypothesis nor the theory of island biogeography adequately explain carabid beetle diversity patterns observed among islands in Lac la Ronge. Instead, we hypothesise that population processes such as higher extinction rates of large-bodied, flightless species and the associated release of smaller-bodied, flying species from intra-guild predation on small islands contribute to observed differences in the structure of carabid assemblages between islands.

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Marine subsidies mediate patterns in avian island biogeography

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.0108 ◽

2020 ◽

Vol 287 (1922) ◽

pp. 20200108

Author(s):

Debora S. Obrist ◽

Patrick J. Hanly ◽

Jeremiah C. Kennedy ◽

Owen T. Fitzpatrick ◽

Sara B. Wickham ◽

...

Keyword(s):

Species Richness ◽

Population Density ◽

Island Biogeography ◽

Forest Edge ◽

Bird Communities ◽

Negative Interaction ◽

Breeding Bird ◽

Island Area ◽

Marine Subsidies ◽

Theory Of 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.

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From Island Biogeography to Conservation: A Multi-Taxon and Multi-Taxonomic Rank Approach in the Tuscan Archipelago

Land ◽

10.3390/land10050486 ◽

2021 ◽

Vol 10 (5) ◽

pp. 486

Author(s):

Enrico Ruzzier ◽

Leonardo Forbicioni ◽

Rodolfo Gentili ◽

Nicola Tormen ◽

Olivia Dondina ◽

...

Keyword(s):

Species Richness ◽

Differential Effect ◽

Island Biogeography ◽

Regression Models ◽

Habitat Diversity ◽

Land Bridge ◽

Taxonomic Rank ◽

Island Area ◽

Species Area ◽

Species Area Relationship

Investigating the drivers that support species richness (S) in insular contexts can give insights for the conservation of insular biodiversity. Our aim was to decouple the effect of drivers (island area, distance from mainland and habitat diversity) accounted in three hypotheses or a combination of them in explaining S in seven islands of the Tuscan Archipelago: Area (species–area relationship, SAR), area and distance from mainland (equilibrium hypothesis, EQH) and habitat (habitat diversity hypothesis, HDH). We used published and original datasets to assess S (except aliens) for 42 taxa (14 animal and 28 plant taxa) in each island, and we used S as the dependent variable and the drivers as covariates in regression models. In 31 taxa, the data supported one of the tested hypotheses or a combination of them, and the most commonly supported hypotheses were SAR (12 taxa) and EQH (10 taxa). The effect of the area was also evident in SAR + HDH (five taxa) and EQH + HDH (one taxon), making it the prevailing driver in explaining S. Since distances are relatively short, and three out of four islands are land-bridge islands, the effect of distance was significant for 12 taxa. The effects of habitat diversity were evident for just nine taxa. The multi-taxon approach allowed us to understand the differential effect of drivers among taxa in influencing S in a single archipelago. Moreover, the multi-taxonomic rank approach highlighted how the information contained within higher taxonomic ranks (e.g., Division) can be substantially different from that derived from lower ranks (e.g., Family). These insights are of particular importance from a conservation perspective of the archipelago’s biodiversity, and this approach can be transferred to mainland fragmented systems.

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A global model of island species–area relationships

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1818190116 ◽

2019 ◽

Vol 116 (25) ◽

pp. 12337-12342 ◽

Cited By ~ 12

Author(s):

Thomas J. Matthews ◽

François Rigal ◽

Kostas A. Triantis ◽

Robert J. Whittaker

Keyword(s):

Species Richness ◽

Structural Equation ◽

Negative Relationship ◽

Equation Model ◽

Local Scale ◽

Ecological Process ◽

Global Pattern ◽

Island Species ◽

Species Area ◽

Globally Distributed

The increase in species richness with island area (ISAR) is a well-established global pattern, commonly described by the power model, the parameters of which are hypothesized to vary with system isolation and to be indicative of ecological process regimes. We tested a structural equation model of ISAR parameter variation as a function of taxon, isolation, and archipelago configuration, using a globally distributed dataset of 151 ISARs encompassing a range of taxa and archipelago types. The resulting models revealed a negative relationship between ISAR intercept and slope as a function of archipelago species richness, in turn shaped by taxon differences and by the amount and disposition of archipelago area. These results suggest that local-scale (intra-archipelago) processes have a substantial role in determining ISAR form, obscuring the diversity patterns predicted by island theory as a function of archipelago isolation. These findings have implications for the use and interpretation of ISARs as a tool within biogeography, ecology, and conservation.

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Predicting community structure in snakes on Eastern Nearctic islands using ecological neutral theory and phylogenetic methods

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2015.1700 ◽

2015 ◽

Vol 282 (1819) ◽

pp. 20151700 ◽

Cited By ~ 10

Author(s):

Frank T. Burbrink ◽

Alexander D. McKelvy ◽

R. Alexander Pyron ◽

Edward A. Myers

Keyword(s):

Community Structure ◽

Island Biogeography ◽

Neutral Theory ◽

Species Abundance ◽

Phylogenetic Methods ◽

Island Communities ◽

Theory Of Island Biogeography ◽

Neutral Theory Of Biodiversity ◽

Neutral Models ◽

Better Than

Predicting species presence and richness on islands is important for understanding the origins of communities and how likely it is that species will disperse and resist extinction. The equilibrium theory of island biogeography (ETIB) and, as a simple model of sampling abundances, the unified neutral theory of biodiversity (UNTB), predict that in situations where mainland to island migration is high, species-abundance relationships explain the presence of taxa on islands. Thus, more abundant mainland species should have a higher probability of occurring on adjacent islands. In contrast to UNTB, if certain groups have traits that permit them to disperse to islands better than other taxa, then phylogeny may be more predictive of which taxa will occur on islands. Taking surveys of 54 island snake communities in the Eastern Nearctic along with mainland communities that have abundance data for each species, we use phylogenetic assembly methods and UNTB estimates to predict island communities. Species richness is predicted by island area, whereas turnover from the mainland to island communities is random with respect to phylogeny. Community structure appears to be ecologically neutral and abundance on the mainland is the best predictor of presence on islands. With regard to young and proximate islands, where allopatric or cladogenetic speciation is not a factor, we find that simple neutral models following UNTB and ETIB predict the structure of island communities.

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Altitudinal diversity gradients and the theory of island biogeography - an explanation

Pacific Conservation Biology ◽

10.1071/pc020213 ◽

2002 ◽

Vol 8 (3) ◽

pp. 213

Author(s):

John Ogden

Keyword(s):

Species Richness ◽

New Zealand ◽

Environmental Variables ◽

Island Biogeography ◽

Environmental Heterogeneity ◽

Causal Agent ◽

Forest Diversity ◽

Island Biogeography Theory ◽

Diversity Gradients ◽

Theory Of Island Biogeography

As part of a wider discussion of forest diversity in New Zealand, Ogden (1995) pointed out that the area available between any pair of contours on a conical mountain decreased with altitude in parallel with the decrease in species richness. This correlation is confounded with other environmental variables, such as temperature, which have been widely considered to be causal in the diversity decline. However, generalization has been elusive, and the supposed causal mechanisms are often couched in vague terms such as "harshness". Ogden chose to emphasize area, and invoked the theory of island biogeography of MacArthur and Wilson (1967) by drawing parallels between islands and successively superimposed areas on mountains. Kingston (this issue) objected, mainly on the grounds that the theory of island biogeography refers to "isolated" areas and deals with the equilibrium between immigration and extinction, on which Ogden presented no evidence. In the light of these criticisms the data presented in Ogden (1995) is re-assessed here. I conclude that the "area hypothesis" is at least as good as any other for "explaining" (correlating with) elevational diversity trends. Area is itself correlated with environmental heterogeneity, which is presumably more important as a causal agent. However, Kingston's insistence on the need for evidence on immigration and extinction to support the application of island biogeography theory is acknowledged.

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Can altitudinal diversity gradients be explained by a reduction in area with altitude?

Pacific Conservation Biology ◽

10.1071/pc020211 ◽

2002 ◽

Vol 8 (3) ◽

pp. 211

Author(s):

Cath Kingston

Keyword(s):

Species Richness ◽

Surface Area ◽

Environmental Conditions ◽

Island Biogeography ◽

Equilibrium Theory ◽

Diversity Gradients ◽

Theory Of Island Biogeography ◽

Reduction In Area

Species richness at higher altitudes of a region typically decreases with altitude, the usual explanation being that environmental conditions become harsher as altitude increases. On conical or ridge shaped mountains the surface area available within equally spaced altitude bands declines as altitude increases. It has been suggested (Ogden 1995) that this may be responsible for the decrease in species richness. The phenomenon of decreasing species richness with altitude has been further interpreted by Ogden as lending support to the equilibrium theory of island biogeography (MacArthur and Wilson 1967) which predicts that larger areas will contain more species. The hypothesis that a decrease in area is responsible for the decline in diversity with altitude is here considered critically, and the evidence presented in support of it is found to be lacking.

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Evaluating the correlation between area, environmental heterogeneity, and species richness using terrestrial isopods (Oniscidea) from the Pontine Islands (West Mediterranean)

Organisms Diversity & Evolution ◽

10.1007/s13127-021-00523-x ◽

2021 ◽

Author(s):

Gabriele Gentile ◽

Roberto Argano ◽

Stefano Taiti

Keyword(s):

Species Richness ◽

Environmental Heterogeneity ◽

Geographic Distance ◽

Habitat Diversity ◽

Tyrrhenian Sea ◽

Island Species ◽

Random Placement ◽

Species Area ◽

Pontine Islands ◽

Volcanic Islands

AbstractArea and environmental heterogeneity influence species richness in islands. Whether area or environmental heterogeneity is more relevant in determining species richness is a central issue in island biogeography. Several models have been proposed, addressing the issue, and they can be reconducted to three main hypotheses developed to explain the species-area relationship: (1) the area-per se hypothesis (known also as the extinction-colonisation equilibrium), (2) the random placement (passive sampling), and the (3) environmental heterogeneity (habitat diversity). In this paper, considering also the possible influence of geographic distance on island species richness, we explore the correlation between area, environmental heterogeneity, and species richness by using faunistic data of Oniscidea inhabiting the Pontine Islands, a group of five small volcanic islands and several islets in the Tyrrhenian Sea, located about 60 km from the Italian mainland. We found that the colonisation of large Pontine Islands may occur via processes independent of geographic distance which could instead be an important factor at a much smaller scale. Such processes may be driven by a combination of anthropogenic influences and natural events. Even in very small-size island systems, environmental heterogeneity mostly contributes to species richness. Environmental heterogeneity could influence the taxocenosis structure and, ultimately, the number of species of Oniscidea via direct and indirect effects, these last mediated by area which may or may not have a direct effect on species richness.

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The species-area relationship: new challenges for an old pattern

Progress in Physical Geography Earth and Environment ◽

10.1177/030913330102500101 ◽

2001 ◽

Vol 25 (1) ◽

pp. 1-21 ◽

Cited By ~ 9

Author(s):

Mark V. Lomolino

Keyword(s):

Secondary Phase ◽

Species Number ◽

General Tendency ◽

Small Islands ◽

Stochastic Variation ◽

Causal Explanations ◽

Island Area ◽

Species Area ◽

Species Area Relationship ◽

The Relationship

The species-area relationship (i.e., the relationship between area and the number of species found in that area) is one of longest and most frequently studied patterns in nature. Yet there remain some important and interesting questions on the nature of this relationship, its causality, quantification and application for both ecologists and conservation biologists. Traditionally, the species-area relationship describes the very general tendency for species number to increase with island area; a relationship whose slope declines (but remains positive) as area increases. The true relationship, however, may be much more complicated than this, and may in many cases approximate a sigmoidal relationship. On small islands, species number may vary independently of island area. Species richness then increases as we consider larger islands, but the curve eventually slows and asymptotes or levels off when richness equals that of the the source or mainland pool. The relationship may also include a secondary phase of increase in richness if island area becomes large enough to allow in situ speciation. Causal explanations for this relationship may, therefore, need to be multifactorial and include a range of processes from disturbance and stochastic variation in habitat quality on the very small islands, to ecological interactions, immigration, extinction and, finally, evolution on the larger islands.

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What Do Ecological Paradigms Offer to Conservation?

International Journal of Ecology ◽

10.1155/2010/250754 ◽

2010 ◽

Vol 2010 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Som B. Ale ◽

Henry F. Howe

Keyword(s):

Species Richness ◽

Biodiversity Conservation ◽

Community Composition ◽

Carrying Capacity ◽

Island Biogeography ◽

Ecological Theory ◽

Theory And Practice ◽

Logistic Growth ◽

Theory Of Island Biogeography ◽

Conservation Plans

Ecological theory provides applications to biodiversity management—but often falls short of expectations. One possibility is that heuristic theories of a young science are too immature. Logistic growth predicts a carrying capacity, but fisheries managed with the Lotka-Volterra paradigm continue to collapse. A second issue is that general predictions may not be useful. The theory of island biogeography predicts species richness but does not predict community composition. A third possibility is that the theory itself may not have much to do with nature, or that empirical parameterization is too difficult to know. The metapopulation paradigm is relevant to conservation, but metapopulations might not be common in nature. For instance, empirical parameterization within the metapopulation paradigm is usually infeasible. A challenge is to determine why ecology fails to match needs of managers sometimes but helps at other. Managers may expect too much of paradigmatic blueprints, while ecologists believe them too much. Those who implement biodiversity conservation plans need simple, pragmatic guidelines based on science. Is this possible? What is possible? An eclectic review of theory and practice demonstrate the power and weaknesses of the ideas that guide conservation and attempt to identify reasons for prevailing disappointment.

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