Comment on ‘Island biogeography: patterns of marine shallow‐water organisms’ by Hachich et al., Journal of Biogeography (2015)

In a recent article, Hachich et al. (2015, Journal of Biogeography, 42 , 1871–1882) studied the large‐scale biogeographical patterns of the species–area, species–island age and species–isolation relationships associated with marine shallow‐water groups (reef fish, gastropods and seaweeds) from 11 Atlantic archipelagos. We here express our concerns regarding the data accuracy used to compute the different models that tested the null hypothesis of species richness being independent of the selected variables. In our commentary, we focus mainly on the use of out‐of‐date checklists of gastropod and seaweed species from different archipelagos, but we also point out inaccuracies in some island age estimates and explain our disagreement with the use of the 200 m depth limit for the shallow‐water gastropods and seaweeds.     

The explanatory power of biogeographical patterns: a reply to de Bruyn et al

Confusion between evidence and hypothesis in biogeographical studies was the focus of our recent Guest Editorial (Parenti & Ebach, 2013, Journal of Biogeography, 40 , 813–820). That editorial was critiqued by de Bruyn et al. (2013, Journal of Biogeography, doi: 10.1111/jbi.12166) to whom we reply briefly here. Despite our shared goals – to understand what lives where and why – we argue from different philosophical premises. Although we may have little common ground, such debate encourages the good health of the field of biogeography.     

Process,correlation and parameter fitting in species distribution models: a response to Kriticos et al

In a recent article (Dormann et al., 2012, Journal of Biogeography, 39, 2119–2131), we compared different approaches to species distribution modelling and depicted modelling approaches along an axis from purely ‘correlative’ to ‘forward process‐based’ models. In their correspondence, Kriticos et al. (2013, Journal of Biogeography, doi: 10.1111/j.1365‐2699.2012.02791.x ) challenge this view, claiming that our continuum representation neglects differences among models and does not consider the ability of fitted process‐based models to combine the advantages of both process‐based and correlative modelling approaches. Here we clarify that the continuum view resulted from recognition of the manifold differences between models. We also reinforce the point that the current trend towards combining different modelling approaches may lead not only to the desired combination of the advantages but also to the accumulation of the disadvantages of those approaches. This point has not been made sufficiently clear previously.     

Island biogeography of Caribbean coral reef fish

Aim The goal of our study was to test fundamental predictions of biogeographical theories in tropical reef fish assemblages, in particular relationships between fish species richness and island area, isolation and oceanographic variables (temperature and productivity) in the insular Caribbean. These analyses complement an analogous and more voluminous body of work from the tropical Indo‐Pacific. The Caribbean is more limited in area with smaller inter‐island distances than the Indo‐Pacific, providing a unique context to consider fundamental processes likely to affect richness patterns of reef fish. Location Caribbean Sea. Methods We compiled a set of data describing reef‐associated fish assemblages from 24 island nations across the Caribbean Sea, representing a wide range of isolation and varying in land area from 53 to 110,860 km². Regression‐based analyses compared the univariate and combined effects of island‐specific physical predictors on fish species richness. Results We found that diversity of reef‐associated fishes increases strongly with increasing island area and with decreasing isolation. Richness also increases with increasing nearshore productivity. Analyses of various subsets of the entire data set reveal the robustness of the richness data and biogeographical patterns. Main conclusions Within the relatively small and densely packed Caribbean basin, fish species richness fits the classical species–area relationship. Richness also was related negatively to isolation, suggesting direct effects of dispersal limitation in community assembly. Because oceanic productivity was correlated with isolation, however, the related effects of system‐wide productivity on richness cannot be disentangled. These results highlight fundamental mechanisms that underlie spatial patterns of biodiversity among Caribbean coral reefs, and which are probably also are functioning in the more widespread and heterogeneous reefs of the Indo‐Pacific.     

The need for richness‐independent measures of turnover when delineating biogeographical regions

Delineating biogeographical regions is one of the primary steps when analysing biogeographical patterns. In their proposed quantitative framework, Kreft & Jetz (2010, Journal of Biogeography, 37 , 2029–2053) recommended the use of the β_sim index to delineate biogeographical regions because this turnover measure is weakly affected by differences in species richness between localities. A recent study by Carvalho et al. (2012, Global Ecology and Biogeography, 21 , 760–771) critiziced the use of β_sim in ecological and biogeographical studies, and proposed the β_‐3 index. Here we used simple numerical examples and an empirical case study (European freshwater fishes) to highlight potential pitfalls associated with the use of β_‐3 for bioregionalization. We show that β_‐3 is not a richness‐independent measure of species turnover. We also show that this index violates the ‘complementarity’ property, namely that localities without species in common have the largest dissimilarity, which is an essential prerequisite for beta diversity studies.     

Putting biogeography’s cart back behind taxonomy’s horse: a response to Triantis et al.

In a recent paper, two of us discussed diversity patterns and diversification processes in the Azores flora. Triantis et al. (2012, Journal of Biogeography, 39, 1179–1184) challenged our hypothesis that palaeoclimatic differences had an effect on diversification rates and suggested that area, island age and isolation explain diversity patterns. They did not, however, fully address the results from our subsequent paper, in which we showed that diversity patterns evident from phylogeographic studies differ markedly from those suggested by checklists. Checklists are working hypotheses and we suggest that the discrepancies evident between molecular data and checklists may be indicative of deficiencies in our taxonomic understanding of the Azores flora. Patterns of molecular and morphological diversity need to be better understood, and the discrepancies between checklists and molecular data accounted for, before we can establish the relative importance of factors such as palaeoclimate, area, island age or isolation in generating endemic diversity patterns in the Azores flora.     

Biogeographical homogeneity of Caribbean coral reef benthos

Caribbean reef benthic assemblages have been considered biogeographically homogeneous at regional scales, but this concept was recently challenged by Williams et al. (2015, Journal of Biogeography, 42 , 1327–1335). These authors concluded that benthic assemblages exhibit considerable biogeographical variability at regional and smaller scales, that rugosity and wave exposure play key roles in structuring assemblages, and that homogenization has yet to occur at a regional scale. We reassess their conclusions using recently published benthic and fish surveys that targeted sites either protected from fishing or intensively overfished. For sponges, regional variation in assemblages is mostly attributable to the removal of chemically undefended species by sponge‐eating fishes at sites protected from overfishing. We maintain that Caribbean benthic assemblages are remarkably homogeneous when compared to reefs in other tropical regions, and were likely more homogeneous before the localized effects of intensive fishing resulted in top‐down ecosystem alterations in benthic assemblages.     

Positive range–abundance relationships in Indo‐Pacific bird communities

Reeve et al. (2016, Ecography, 39 , 990–997) recently reported negative range–abundance relationships in Indo‐Pacific bird communities and speculated that geographical isolation facilitates the evolution of broad‐niched, small‐ranged and abundant species. We tested this relationship using a large independent data set on range and abundance of birds across New Caledonia (over 4,000 bird census points for 17,300 km²). In contradiction to Reeve et al. (2016, Ecography, 39 , 990–997), we found clear evidence that range–abundance relationships are positive and endemic species have narrower habitat niches than wide‐range species. Our findings are likely valid also for other islands in the Indo‐Pacific.     

Pike (Esox lucius) could have been an exclusive human introduction to Ireland after all: a comment on Pedreschi et al. (2014)

A recent publication (Pedreschi et al., 2014, Journal of Biogeography, 41 , 548–560) casts doubt over the status of pike (Esox lucius) as a non‐native species in Ireland by reporting two distinct genetic groups of pike present: one a human introduction in the Middle Ages, the other hypothesized to result from natural colonization after the Last Glacial Maximum (LGM). While the existence of two groups is not disputed, the hypothesized natural colonization scenario conflicts with the sequence in which the islands of Britain and Ireland became isolated from Europe after the LGM. An alternative natural colonization scenario raised herein was rejected, leaving an earlier, two‐phase, human introduction of pike from Britain or Europe to Ireland as a realistic alternative hypothesis explaining the results of Pedreschi et al. (2014). This leaves the debates on human introduction versus natural colonization, introduced versus native species status, and pike management in Ireland wide open.     

Towards a balanced view of pike in Ireland: a reply to Ensing

In our recent study of the population genetics of pike (Esox lucius) in Ireland (Pedreschi et al., 2014 , Journal of Biogeography, 41 , 548–560), we reported the existence of two main demographic units and showed that these may correspond to two independent and temporally staggered colonization events, the first of which may have been too old to be caused or assisted by human translocations. Ensing (2015, Journal of Biogeography, doi: 10.1111/jbi.12410 ) first used our genotypic data to explore alternative historical scenarios, then attempted to reconcile the ‘two‐wave’ colonization process of Ireland by pike with translocation activities by humans in Neolithic/Bronze age times. Here we illustrate why the evidence base for Ensing's reconstruction is weak and we outline a realistic strategy to better understand the role of pike in Irish freshwater ecosystems.     

On cladistics and human–ape relationships

The rebuttal of our correspondence (Lehtonen et al., Journal of Biogeography, 2011, 38, 805–808) by J. R. Grehan and J. H. Schwartz (Journal of Biogeography, 2011, 38, 2397–2404) reveals logical inconsistencies in their methodology. Here, we provide a clarification of these issues.     

New Caledonian biogeography: a reply to Murienne

This note replies to criticisms raised by Murienne (Journal of Biogeography, 2010, doi: 10.1111/j.1365‐2699.2010.02321.x ). Herein it is argued that assuming distributions in New Caledonia are caused by current environmental factors overlooks the possible importance of regional tectonic history for the biogeography.     

Oceanic island biogeography through the lens of the general dynamic model: assessment and prospect

The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non‐equilibrium framework generating novel predictions for emergent diversity properties of oceanic islands and archipelagos. Its publication in 2008 coincided with, and spurred on, renewed attention to the dynamics of remote islands. We review progress, both in testing the GDM's predictions and in developing and enhancing ecological–evolutionary understanding of oceanic island systems through the lens of the GDM. In particular, we focus on four main themes: (i) macroecological tests using a space‐for‐time rationale; (ii) extensions of theory to islands following different patterns of ontogeny; (iii) the implications of GDM dynamics for lineage diversification and trait evolution; and (iv) the potential for downscaling GDM dynamics to local‐scale ecological patterns and processes within islands. We also consider the implications of the GDM for understanding patterns of non‐native species diversity. We demonstrate the vitality of the field of island biogeography by identifying a range of potentially productive lines for future research.     

Island biogeography of bats in Baja California, Mexico: patterns of bat species richness in a near-shore archipelago

Aim We studied the relationship between the size and isolation of islands and bat species richness in a near‐shore archipelago to determine whether communities of vagile mammals conform to predictions of island biogeography theory. We compared patterns of species richness in two subarchipelagos to determine whether area per se or differences in habitat diversity explain variations in bat species richness. Location Islands in the Gulf of California and adjacent coastal habitats on the Baja California peninsula in northwest Mexico. Methods Presence–absence surveys for bats were conducted on 32 islands in the Gulf of California using acoustic and mist‐net surveys. We sampled for bats in coastal habitats of four regions of the Baja peninsula to characterize the source pool of potential colonizing species. We fitted a semi‐log model of species richness and multiple linear regression and used Akaike information criterion model selection to assess the possible influence of log₁₀ area, isolation, and island group (two subarchipelagos) on the species richness of bats. We compared the species richness of bats on islands with greater vegetation densities in the southern gulf (n = 20) with that on drier islands with less vegetation in the northern gulf (n = 12) to investigate the relationship between habitat diversity and the species richness of bats. Results Twelve species of bats were detected on islands in the Gulf of California, and 15 species were detected in coastal habitats on the Baja peninsula. Bat species richness was related to both area and isolation of islands, and was higher in the southern subarchipelago, which has denser vegetation. Log₁₀ area was positively related to bat species richness, which increased by one species for every 5.4‐fold increase in island area. On average, richness declined by one species per 6.25 km increase in isolation from the Baja peninsula. Main conclusions Our results demonstrate that patterns of bat species richness in a near‐shore archipelago are consistent with patterns predicted by the equilibrium theory of island biogeography. Despite their vagility, bats may be more sensitive to moderate levels of isolation than previously expected in near‐shore archipelagos. Differences in vegetation and habitat xericity appear to be associated with richness of bat communities in this desert ecosystem. Although observed patterns of species richness were consistent with those predicted by the equilibrium theory, similar relationships between species richness and size and isolation of islands may arise from patch‐use decision making by individuals (optimal foraging strategies).     

Ecologically flexible endemics dominate Indo‐Pacific bird communities

Reeve et al. (2016, Ecography, 39 , 990‐997) found that ecologically flexible endemics dominate Indo‐Pacific bird communities. This negative relationship between local abundance and global range size contrasts strongly with the positive range size‐abundance relationship “rule,” which would predict community dominance by globally widespread species. Theuerkauf et al. (2017, Journal of Biogeography, 44 , 2161–2163) provide new data from New Caledonia which they claim invalidate our study. They find positive relationships between local abundance and local range size, which they attribute to endemic species having narrower habitat niches than globally widespread species. We reanalysed their data using global range sizes, corroborating the pattern we originally reported: negative relationships between local abundance and global range size, driven by a subset of adaptable endemic species. We stress the importance of being explicit about the scale of ecological mechanisms, and ensuring that the scale of analysis matches the scale of interpretation.     

Towards a ‘Sea‐Level Sensitive’ dynamic model: impact of island ontogeny and glacio‐eustasy on global patterns of marine island biogeography

A synthetic model is presented to enlarge the evolutionary framework of the General Dynamic Model (GDM) and the Glacial Sensitive Model (GSM) of oceanic island biogeography from the terrestrial to the marine realm. The proposed ‘Sea‐Level Sensitive’ dynamic model (SLS) of marine island biogeography integrates historical and ecological biogeography with patterns of glacio‐eustasy, merging concepts from areas as diverse as taxonomy, biogeography, marine biology, volcanology, sedimentology, stratigraphy, palaeontology, geochronology and geomorphology. Fundamental to the SLS model is the dynamic variation of the littoral area of volcanic oceanic islands (defined as the area between the intertidal and the 50‐m isobath) in response to sea‐level oscillations driven by glacial–interglacial cycles. The following questions are considered by means of this revision: (i) what was the impact of (global) glacio‐eustatic sea‐level oscillations, particularly those of the Pleistocene glacial–interglacial episodes, on the littoral marine fauna and flora of volcanic oceanic islands? (ii) What are the main factors that explain the present littoral marine biodiversity on volcanic oceanic islands? (iii) How can differences in historical and ecological biogeography be reconciled, from a marine point of view? These questions are addressed by compiling the bathymetry of 11 Atlantic archipelagos/islands to obtain quantitative data regarding changes in the littoral area based on Pleistocene sea‐level oscillations, from 150 thousand years ago (ka) to the present. Within the framework of a model sensitive to changing sea levels, we discuss the principal factors affecting the geographical range of marine species; the relationships between modes of larval development, dispersal strategies and geographical range; the relationships between times of speciation, modes of larval development, ecological zonation and geographical range; the influence of sea‐surface temperatures and latitude on littoral marine species diversity; the effect of eustatic sea‐level changes and their impact on the littoral marine biota; island marine species–area relationships; and finally, the physical effects of island ontogeny and its associated submarine topography and marine substrate on littoral biota. Based on the SLS dynamic model, we offer a number of predictions for tropical, subtropical and temperate volcanic oceanic islands on how rates of immigration, colonization, in‐situ speciation, local disappearance, and extinction interact and affect the marine biodiversity around islands during glacials and interglacials, thus allowing future testing of the theory.     

Darwin’s Galapagos gourd: providing new insights 175 years after his visit

The year 2010 marks the 175th anniversary of Charles Darwin’s visit to the Galapagos Islands. A recent paper by J. C. Briggs, ‘Darwin’s biogeography’ (Journal of Biogeography, 2009, 36 , 1011–1017), summarizes Darwin’s contributions to the field of biogeography, stressing the importance of his natural history specimens. Here, we illustrate how a plant collected by Darwin during his visit to Floreana and not collected since can provide insights into dispersal to oceanic islands as well as extinction of island plants, based on ancient DNA from Darwin’s herbarium specimen.     

Pyrogeography,historical ecology,and the human dimensions of fire regimes

In our 2011 synthesis (Bowman et al., Journal of Biogeography, 2011, 38 , 2223–2236), we argued for a holistic approach to human issues in fire science that we term ‘pyrogeography’. Coughlan & Petty (Journal of Biogeography, 2013, 40 , 1010–1012) critiqued our paper on the grounds that our ‘pyric phase’ model was built on outdated views of cultural development, claiming we developed it to be the unifying explanatory framework for all human–fire sciences. Rather, they suggest that ‘historical ecology’ could provide such a framework. We used the ‘pyric transition’ for multiple purposes but did not offer it as an exclusive explanatory framework for pyrogeography. Although ‘historical ecology’ is one of many useful approaches to studying human–fire relationships, scholars should also look to political and evolutionary ecology, ecosystems and complexity theories, as well as empirical generalizations to build an interdisciplinary fire science that incorporates human, ecological and biophysical dimensions of fire regimes.     

Termite mounds alter the spatial distribution of African savanna tree species: artefacts and real patterns

In a recent issue (vol. 43) of the Journal of Biogeography, Davies et al. (2015) presented novel analyses of the spatial distribution of tree species around termite mounds in a South African savanna. However, some of their conclusions are not supported by the data. My aim in this correspondence is to point out some limitations of their analyses, stimulate cautious interpretation of their results and suggest better methods for future use.     

Outlier detection methods are still effective even using virtual species created with the probabilistic approach

Liu et al. (Journal of Biogeography, 2018, 45 :164–176) presented an approach to detect outliers in species distribution data by developing virtual species created using the threshold approach. Meynard et al. (Journal of biogeography, 2019, 46 :2141–2144) raised concerns about this approach stating that ‘using a probabilistic approach … may significantly change results’. Here we provide a new series of simulations using the two approaches and demonstrate that the outlier detection approach based on pseudo species distribution models was still effective when using the probabilistic approach, although the detection rate was lower than when using the threshold approach.