Equilibrium Theory Of Island Biogeography Research Articles

A niche-based theory of island biogeography.

The equilibrium theory of island biogeography (ETIB) is a widely applied dynamic theory proposed in the 1960s to explain why islands have coherent differences in species richness. The development of the ETIB was temporarily challenged in the 1970s by the alternative static theory of ecological impoverishment (TEI). The TEI suggests that the number of species on an island is determined by its number of habitats or niches but, with no clear evidence relating species richness to the number of niches however, the TEI has been almost dismissed as a theory in favour of the original ETIB. Here, we show that the number of climatic niches on islands is an important predictor of the species richness of plants, herpetofauna and land birds. We therefore propose a model called the niche-based theory of island biogeography (NTIB), based on the MacroEcological Theory on the Arrangement of Life (METAL), which successfully integrates the number of niches sensu Hutchinson into ETIB. To account for greater species turnover at the beginning of colonisation, we include higher initial extinction rates. When we test our NTIB for resident land birds in the Krakatau Islands, it reveals a good correspondence with observed species richness, immigration and extinction rates. Provided the environmental regime remains unchanged, we estimate that the current species richness at equilibrium is ~45 species (range between 38.39 and 61.51). Our NTIB provides better prediction because it counts for changes in species richness with latitude, which is not considered in any theory of island biogeography.

Plant diversity on islands in the Anthropocene: Integrating the effects of the theory of island biogeography and human activities

Understanding how the complexities of biodiversity are maintained on islands has long been one of the central issues studied in conservation biology. With the global onset of anthropogenically driven biodiversity changes, the influence of anthropogenic activities challenges the applicability of the widely accepted Equilibrium Theory of Island Biogeography (ETIB). This study aimed to test how island area, isolation (MD: distance to the mainland, and ND: distance to the nearest island), and human activities (habitat heterogeneity, and proportion of road area relative to island area to refer to the human impact on island) separately and jointly affect the species diversity of vascular plants. The number of plant species with different growth forms (woody plants, herbs, and lianas) was calculated on 35 islands in Sanyang Wetland, which is a human-dominated wetland near the highly populated city of Wenzhou, China. We also evaluated the relative importance of these variables on the number of species using a random forest analysis. The number of species increased with increasing island area and habitat heterogeneity and decreased with increasing isolation for different growth forms. A significant, positive relationship was observed between the number of species and the proportion of road area for herbs, but not for woody plants and lianas. Habitat heterogeneity was the most important predictor for all plants, the proportion of road area was the most important predictor for herbs, and MD was the most important predictor for woody plants and lianas. These results indicate that ETIB remains relevant in the context of human disturbance, but the relative importance of ecological processes on species diversity differs significantly among plant growth forms. Therefore, we should consider plant functional groups when testing multifactorial effects on species diversity on human-dominated islands.

Journal of Biogeography Innovation Awards, 2023

Journal of Biogeography Innovation Awards, 2023

Island biogeography of soundscapes: Island area shapes spatial patterns of avian acoustic diversity

AbstractAimThe equilibrium theory of island biogeography predicts the positive species–area relationship and the negative species–isolation relationship, resulting in higher species richness on large and close islands. Unlike species richness, soundscape diversity integrates sound from various sources (e.g. biophony, geophony and anthrophony). However, how soundscape diversity varies with island area and isolation still needs to be tested. Here, we explored the island biogeography of bird soundscapes and the determinants of island attributes in shaping bird diversity and soundscape diversity.LocationThousand Island Lake, Zhejiang, China.TaxonBirds.MethodsWe recorded avian soundscapes by audio recorders and censused bird diversity by line transects on 20 land‐bridge islands. We calculated four acoustic indices (acoustic complexity index, bioacoustic index, acoustic evenness index and acoustic entropy index) to assess acoustic richness, evenness and heterogeneity to explore the soundscape diversity of birds. We used multiple linear regressions, spatial autoregressions and piecewise structural equation models to examine the relationships between bird richness and acoustic diversity, and island attributes.ResultsWe found positive diversity–area relationships for avian soundscapes. Larger islands had more vocal species and higher habitat diversity, which led to an increment in the richness and unevenness of avian soundscapes on large islands. Acoustic evenness decreased with increasing isolation (distance to the mainland).Main ConclusionsSoundscapes on large islands are more diverse than those on small islands. Rich acoustic assemblages and heterogeneous habitats promote increased soundscape diversity on islands. Conversely, the lack of vocal contributors, resulting in a decrement in the communication of acoustic signals, can create a lower soundscape diversity on small and remote islands. Our study emphasizes the necessity of examining both species and habitat diversity in island biogeography for better understanding the underlying mechanisms determining biological soundscapes on islands.

Nearby large islands diminish biodiversity of the focal island by a negative target effect.

The Equilibrium Theory of Island Biogeography postulates that larger and closer islands support higher biodiversity through the dynamic balance of colonization and extinction processes. The negative diversity-isolation (i.e. the distance to the mainland) relationship is derived based on the assumption that the mainland is the only source pool for island biotas. However, nearby islands could also act as species sources for focal islands via a source effect. In this study, we move a further step and hypothesize that nearby islands may reduce bird colonizers of the focal island and diminish its biodiversity, resulting in a negative target effect. To test our hypothesis, we assessed the effects of island area and isolation (metrics considering both the mainland and nearby islands) on taxonomic (i.e. species richness), functional and phylogenetic diversity of terrestrial breeding birds on 42 islands in the largest archipelago of China, the Zhoushan Archipelago. Furthermore, we compared the predictive power of the distance to the large island under a set of relative area thresholds and the relative area of nearby islands on species richness under a set of distance thresholds to explore the role of nearby islands as a source and/or target island. We found that island area had a positive effect on species richness, phylogenetic diversity and functional diversity, while the distance to the mainland had a negative effect only on species richness. Species richness on the focal island increased with increasing distance to the nearest larger island, indicating the negative target effect. Furthermore, the negative target effect depended on the area of nearby islands relative to the area of the focal island. Our finding of the negative target effect suggests islands located between the mainland and the focal island can be not only sources or stepping stones, but also colonization targets. This result demonstrates the importance of considering multiple geographical attributes of islands in island biogeographic studies, especially the characteristics related to source and/or target effects.

ETIB‐T: An Equilibrium Theory of Island Biogeography for plant traits

AbstractAimThe Equilibrium Theory of Island Biogeography (ETIB) posits that species richness on islands represents a dynamic equilibrium between immigration and extinction. ETIB makes predictions about numbers of species and biogeographical rates, but not about species identities or functional traits. However, functional traits provide additional information in understanding the assembly of island biotas. Here, we build on ETIB's principle of community equilibria and investigate how these processes affect plant functional traits over time.LocationFifteen islands from 164 m2 to 19 km2 in Western Australia.TaxonAngiosperms.MethodsWe assembled an island‐trait dataset linking seed mass, plant height and leaf area of 156 species to their occurrences on 15 islands sampled four times within four decades. We estimated community trait means and functional diversity for each island and sampling period and tested whether both remained at equilibrium over time. Using linear models, we tested whether temporal species turnover is linked to specific traits. We used generalised linear mixed‐effect models to test for the effect of environmental characteristics on species and trait turnover.ResultsSpecies richness on the islands was at equilibrium as predicted by ETIB despite high species temporal turnover. Functional diversity and community trait means also were stable over time. Species most susceptible to turnover were on average smaller and had lower seed mass than persisting species. Environmental island characteristics had no strong effect in explaining species and trait turnover.Main conclusionsWe provide evidence that ETIB can be extended to functional traits, which we suggest to term Equilibrium Theory of Island Biogeography for Traits. Trait equilibria on islands suggest that locally extinct species are replaced by new ones sharing similar traits. Being small with light seeds increases both immigration probability and extinction risk.

In Memoriam : Edward O. Wilson (1929-2021): It All Started with Ants.

In Memoriam : Edward O. Wilson (1929-2021): It All Started with Ants.

From island biogeography to landscape and metacommunity ecology: A macroecological perspective of bat communities

The equilibrium theory of island biogeography and its quantitative consideration of origination and extinction dynamics as they relate to island area and distance from source populations have evolved over time and enriched theory related to many disciplines in spatial ecology. Indeed, the island focus was catalytic to the emergence of landscape ecology and macroecology in the late 20th century. We integrate concepts and perspectives of island biogeography, landscape ecology, macroecology, and metacommunity ecology, and show how these disciplines have advanced the understanding of variation in abundance, biodiversity, and composition of bat communities. We leverage the well-studied bat fauna of the islands in the Caribbean to illustrate the complex interplay of ecological, biogeographical, and evolutionary processes in molding local biodiversity and system-wide structure. Thereafter, we highlight the role of habitat loss and fragmentation, which is increasing at an accelerating rate during the Anthropocene, on the structure of local bat communities and regional metacommunities across landscapes. Bat species richness increases with the amount of available habitat, often forming nested subsets along gradients of patch or island area. Similarly, the distance to and identity of sources of colonization influence the richness, composition, and metacommunity structure of islands and landscape networks.

Biogeographic and anthropogenic correlates of Aleutian Islands plant diversity: A machine‐learning approach

AbstractThis is the first comprehensive analysis of vascular plant diversity patterns in the Aleutian Islands to identify and quantify the impact of Aleutian Island distance dispersal barriers, geographical, ecological and anthropogenic factors. Data from public Open Access databases, printed floristic accounts, and from collections made by the primary author were used to develop an Aleutian floristic database. The most common plant distribution pattern was “an eastern origin community”, though it compared similarly to the “Western” and “Widespread” distribution pattern. We established an ecological plant community composition class for each island, based on clustering species assemblage dissimilarity measurements (Jaccard Index), and a measurement of phylogenetic dissimilarity (UniFrac). We modelled these composition classes and species richness values in non‐parametric algorithmic models and concepts (data cloning using machine learning, stochastic boosting‐ TreeNet) based on classic and Aleutians‐specific island biogeography hypotheses. Plant species richness is strongly associated with the equilibrium model variables of area and island isolation, as well as distance to the Alaska Peninsula, and island total stream length. Species composition is strongly associated with the landmass groups during the last glacial maximum, maximum island elevation, island isolation and island area. Phylogenetic composition is associated with island area, distance from the islands to the Chukotka Peninsula, maximum island elevation, island geologic age, and island isolation. This study extends the equilibrium theory of island biogeography by including additional drivers of diversity during the Anthropocene, such as the landmass during the LGM, as well as factors that may be related to anthropogenic extinction rate.

Area, isolation, disturbance and age effects on species richness of summer waterbirds in post-mining subsidence lakes, Anhui, China

BackgroundThe species–area relationship is one of the best documented patterns in community ecology. Factors influencing species–area relationship are still not well understood. Since the proposal of the equilibrium theory of island biogeography, many studies have tested the effects of area and isolation, estimating effects of disturbance and patch age were scarce and should also be important bearing.MethodsWe investigated summer waterbird species richness in 38 post-mining subsidence lakes in Huainan and Fuyang, Anhui, China, May 25–June 12, 2016. We examined the effects of lake area, isolation (distance to natural water bodies), aquaculture disturbance, lake age and lake state (still sinking or not sinking) on summer waterbird species richness with multivariable linear regression method and model selection method.ResultsOur results from multivariable linear regression and model selection were consistent, which showed that species richness was positively related with lake area and negatively related with isolation. Aquaculture disturbance negatively influenced species richness. Highest species richness were found in lakes under intermediate intensity of aquaculture activities with area less than 100 ha and lakes under low intensity of aquaculture activities with area greater than 100 ha. Lake age and lake state had no significant effects on species richness.ConclusionsSpecies richness was most related with lake area, aquaculture disturbance, and isolation, with lake area had a positive effect, while aquaculture activities and isolation had a negative effect. What’s more, aquaculture activities significantly changed the slope of species–area relationship and might impede us finding a relationship between species richness and lake age.

Great theories of species diversity in space and why they were forgotten: The beginnings of a spatial ecology and the Nordic early 20th‐century botanists

AbstractSometimes, we stumble over literature revealing that well‐known and groundbreaking theories have previously been proposed by earlier researchers. Going back to the 1920s and a group of Nordic botanists, we discovered that they had already accomplished much of what theoretical ecologists and biographers, especially Americans, did half a century later. In order to restore their legacy and understand why the work of the early spatial ecologists in Scandinavia and Finland was forgotten, we examined their publications, recalculated some of their results from their original data and compared these to the more recent independent discoveries of these theories. These Nordic early 20th‐century botanists worked with sample areas (mainlands) as well as island systems, examining spatial patterns and foreseeing or even building probabilistic approaches to species–area relationships (SARs), occupancy‐frequency distributions (OFDs) and species‐to‐genus (S/G) ratios. Many theories in spatial ecology and biogeography are linked to the SAR, such as MacArthur and Wilson's equilibrium theory of island biogeography (based on colonization and extinction), Darlington's rule of thumb, Preston's canonical hypothesis, Diamond's rules of reserve design, and Coleman's random‐placement theory. However, many of the most important SAR‐based theories—as the mathematical shape of both mainland and island SARs as well as rules of thumb, colonization rates on islands, and the random‐placement theory—had already been discovered or discussed in the 1920s by members of the Stockholm group which included the Swedes Gunnar Romell, Olof Arrhenius, Harald Kylin, and The Svedberg, and a Finn, Widar Brenner. The notion of stochastic S/G ratios and the idea that distance affects colonization rates can be traced back to another Finn, Alvar Palmgren. Great theories like these may disappear, if they are, as these, buried in obscure journals or written in languages other than English. There was also almost no audience in the 1920s and 30s, as mathematical theories were less acceptable at that time. Perhaps even more importantly, a devastating dispute (“The Great Polemic”) arose between the Stockholm group of theoretically and mathematically inclined botanists and the Uppsala group of descriptive phytosociologists. The fight, in which the Uppsala group won, was more a political and sociological than an intellectual one. As a result, not only the budding discipline of spatial ecology faded into oblivion but also the researchers were lost to science, at least to spatial ecology and biogeography, and descriptive and taxonomic approaches came to dominate Nordic ecology right up to the 1960s.

Mosquitoes in urban green spaces: using an island biogeographic approach to identify drivers of species richness and composition

Mosquitoes are well known for their epidemiological importance as vectors of a wide range of human pathogens. Despite the many studies on medically important species, little is known about the diversity patterns of these insects in urban green spaces, which serve as shelter and refuge for many native and invasive species. Here, we investigate drivers of mosquito richness and composition in nine urban parks in the city of São Paulo, Brazil. Using the equilibrium theory of island biogeography, we tested predictive models for species richness and composition and performed nestedness analysis. We also investigated whether species loss tends to benefit vector mosquitoes. In the period 2011 to 2013, a total of 37,972 mosquitoes belonging to 73 species and 14 genera were collected. Our results suggest there is a species-area relationship, an increase in species similarity as richness is lost and a nested species composition pattern. Seven of the eight most commonly found species are considered vectors of human pathogens, suggesting a possible link between species loss and increased risk of pathogen transmission. Our data highlight the need for studies that seek to understand how species loss may affect the risk of infectious diseases in urban areas.

Island biogeography of insect conservation in urban green spaces

SUMMARYBecause of their isolation, biotic communities of urban green spaces are expected to be similar to those of oceanic islands. This should be particularly true for insects, which represent an important component of urban faunas. The equilibrium theory of island biogeography (ETIB) allows for the formulation of some hypotheses regarding the influence of the geographical characteristics of green spaces on insect species richness and extinction risk. Based on island biogeography principles, we present eight predictions on how green space characteristics should influence insect species richness and loss. We analysed the current literature in order to determine which predictions were supported and which were not. We found that many studies gave outcomes that support ETIB predictions about the effects of area and isolation of green spaces; we found no strong support for predictions about shape and extent of native habitat in the literature that we reviewed. Most of the available studies dealt with patterns in species richness, whereas insect species loss has been rarely investigated. Future developments in the application of island biogeography principles to urban insect conservation should address temporal trends in species persistence and the analysis of species co-occurrence and nestedness.

Influences on recovery of seabirds on islands where invasive predators have been eradicated, with a focus on Procellariiformes

AbstractProtecting seabirds is a global conservation priority given that 29% of seabird species are threatened with extinction. One of the most acute threats to seabirds is the presence of introduced predators, which depredate seabirds at all life stages, from eggs to adults. Consequently, eradication of invasive predators has been identified as an effective and commonly used approach to seabird conservation. Seabird recovery following the eradication of predators is influenced by complex and interacting environmental and demographic factors, and there are gaps in our understanding of species-specific responses. We reflect on the recovery of seabirds on islands cleared of predators, drawing on the equilibrium theory of island biogeography, and synthesize key influences on recovery reported in the literature. We present a regionally specific case study on the recovery of seabird colonies (n = 98) in the Hauraki Gulf, New Zealand, which is a hotspot of seabird diversity (27 species), with a long history of eradications of invasive predators. We found that on islands cleared of predators seabirds recover over time, and such islands have more diverse seabird assemblages than islands that never had predators. Recovery appears to be influenced by a suite of site- and species-specific factors. Managers may assume that given enough time following eradication of predators, seabirds will recolonize an island. Although time is a factor, proximity to source populations and human activities has a significant effect on recolonization by seabirds, as do demographic traits, colonizing ability and habitat suitability. Therefore, integrating expected site and species-specific recovery responses in the planning of eradications should help guide post-eradication management actions.

Trapped in the web of water: Groundwater-fed springs are island-like ecosystems for the meiofauna.

We investigated whether the equilibrium theory of island biogeography (ETIB) can be applied to the meiofauna of groundwater‐fed springs. We tested whether copepod species richness was related with spring area, discharge, and elevation. Additionally, five hypotheses are tested based on species distribution patterns, dispersal ability, and life‐history characteristics of several guilds (stygobiotic, nonstygobiotic, cold stenotherm, and noncold stenotherm species). Thirty springs in the central Apennines (Italy) were considered. A multimodel selection procedure was applied to select best‐fit models using both ordinary least‐squares regressions and autoregressive models. Mantel tests were used to investigate the impact of spatial autocorrelation in determining interspring similarity (ßsor), pure turnover (ßsim), intersite nestedness (ßnest = ßsor − ßsim), and matrix nestedness (measured using NODF and other metrics). Explicit consideration of spatial correlations reduced the importance of predictors of overall species richness, noncold stenotherm species (both negatively affected by elevation), cold stenotherm species, and nonstygobiotic species, but increased the importance of area for the stygobiotic species. We detected nested patterns in all cases, except for the stygobites. Interspring distances were positively correlated with ßsor and ßnest (but not with ßsim) for the entire data set and for nonstygobiotic, cold stenotherm, and noncold stenotherm species. In the case of stygobites, interspring geographical distances were marginally correlated with ßsor and no correlation was found for ßsim and ßnest. We found support for ETIB predictions about species richness, which was positively influenced by area and negatively by elevation (which expresses the size of source of immigrants). Low turnover and high nestedness are consistent with an equilibrium scenario mainly regulated by immigration and extinction. Stygobites, which include many distributional and evolutionary relicts, have a low capability to disperse through the aquifers and tend to be mainly confined to the springs where they drifted out and were trapped by springbed sediments.

A generalization of the taxon cycle

A generalization of the taxon cycle

Insects and the city: what island biogeography tells us about insect conservation in urban areas

Abstract. Habitat fragmentation caused by urbanization is considered a prominent threat to biodiversity. Urban development creates a mosaic of natural fragments which can be occupied by organisms able to survive in small spaces. These fragments are a set of habitat islands separated by less suitable non-native habitats. Because of their isolation, communities of urban green spaces can be investigated using hypotheses developed in island biogeography. The "equilibrium theory of island biogeography" (ETIB) allows the formulation of some predictions about how various characteristics of green spaces (such as their area, shape, level of isolation, environmental heterogeneity, age) should influence species richness. Many studies found support for ETIB predictions, but results varied considerably according to the species' sensitivity to patch size, matrix characteristics, and history of the city. In some cases ETIB predictions were falsified. These contrasting results warn against making generalizations on conservation strategies only based on ETIB models. On the other hand, the ETIB may represent a useful framework for urban conservation, especially for small animals like insects, if the roles of other factors, such as the surrounding landscape, the specific needs of the species under study, and the history of the urbanization process, are taken into account.

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

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.

Biogeography in the early twenty-first century: A science with increasing significance for Earth’s changes and challenges

Biogeography is, in essence, the geography of nature or more specifically, the study of the distribution of Earth’s life forms at all spatial and temporal scales. This paper traces the historical development of biogeography from ancient times to the twenty-first century, highlights contemporary trends and expansions, and previews future prospects. The cumulative discovery of biogeographic patterns culminated in the development of the theory of evolution – biogeography’s greatest contribution to science. The paradigm shift to causal approaches in the early twentieth century led to ecological biogeography emerging as the second pillar of biogeography in addition to historical biogeography. Fostered by the acceptance of plate tectonics, the equilibrium theory of island biogeography, the rapid advancement of new perspectives and methods in historical biogeography, and revolutionary advances in compiling, visualizing, and analyzing spatially explicit information, biogeography evolved into a rigorous science during the second half of the twentieth century. Currently, major active sub-fields are phylogeography, macroecology, and conservation biogeography. Biogeography is on the way to becoming a ‘big science’, entering an era of increasingly integrative and multi-faceted approaches, increasingly accessible and available data, tools, and techniques, and interdisciplinary collaboration.

Predicting biodiversity change and averting collapse in agricultural landscapes

The equilibrium theory of island biogeography is the basis for estimating extinction rates and a pillar of conservation science. The default strategy for conserving biodiversity is the designation of nature reserves, treated as islands in an inhospitable sea of human activity. Despite the profound influence of islands on conservation theory and practice, their mainland analogues, forest fragments in human-dominated landscapes, consistently defy expected biodiversity patterns based on island biogeography theory. Countryside biogeography is an alternative framework, which recognizes that the fate of the world's wildlife will be decided largely by the hospitality of agricultural or countryside ecosystems. Here we directly test these biogeographic theories by comparing a Neotropical countryside ecosystem with a nearby island ecosystem, and show that each supports similar bat biodiversity in fundamentally different ways. The island ecosystem conforms to island biogeographic predictions of bat species loss, in which the water matrix is not habitat. In contrast, the countryside ecosystem has high species richness and evenness across forest reserves and smaller forest fragments. Relative to forest reserves and fragments, deforested countryside habitat supports a less species-rich, yet equally even, bat assemblage. Moreover, the bat assemblage associated with deforested habitat is compositionally novel because of predictable changes in abundances by many species using human-made habitat. Finally, we perform a global meta-analysis of bat biogeographic studies, spanning more than 700 species. It generalizes our findings, showing that separate biogeographic theories for countryside and island ecosystems are necessary. A theory of countryside biogeography is essential to conservation strategy in the agricultural ecosystems that comprise roughly half of the global land surface and are likely to increase even further.