Category Archives: Biogeography

Pollinator availability, mating system and variation in flower morphology in a tropical savanna tree – a new, open-access study

Curatella image by Pedro Lorenzo

Widespread plant species can encounter a variety of different pollinators across their distributional range.  This in turn can result in local adaptation of flowers to particular pollinators, or to an absence of pollinators that results in adaptations for more self pollination.   A newly published study by one of my former PhD students, André Rodrigo Rech in Brazil, has looked at this in the widespread South American savanna tree Curatella americana.  André studied 10 populations separated in space by thousands of kilometres, in cerrado vegetation, one of the most threatened habitat types in Brazil.  Here’s the abstract:

Widely distributed organisms face different ecological scenarios throughout their range, which can potentially lead to micro-evolutionary differentiation at specific localities. Mating systems of animal pollinated plants are supposed to evolve in response to the availability of local pollinators, with consequent changes in flower morphology. We tested the relationship among pollination , mating system, and flower morphology over a large spatial scale in Brazilian savannas using the tree Curatella americana (Dilleniaceae). We compared fruit set with and without pollinators in the field, and analyzed pollen tube growth from self- and cross-pollinated flowers in different populations. Populations with higher natural fruit set also had lower fruit set in bagged flowers, suggesting stronger barriers to self-fertilization. Furthermore, higher levels of autogamy in field experiments were associated with more pollen tubes reaching ovules in self-pollinated flowers. Morphometric studies of floral and leaf traits indicate closer-set reproductive organs, larger stigmas and smaller anthers in populations with more autogamy. We show that the spatial variation in mating system, flower morphology and pollination previously described for herbs also applies to long-lived, perennial tropical trees, thus reemphasizing that mating systems are a population-based attribute that vary according to the ecological scenario where the plants occur

Here’s the full citation with a link to the paper which is open access:

Rech, A.R., Ré Jorge, L., Ollerton, J. & Sazima, M. (2018) Pollinator availability, mating system and variation in flower morphology in a tropical savannah tree. Acta Botanica Brasilica (in press)

The illustration of Curatella americana  and its pollinators is by Pedro Lorenzo.

This paper is a contribution to a special issue of Acta Botanica Brasilica dedicated to floral biology and pollination biology in Brazil It’s all open access and if you follow that link you can download the papers.

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Filed under Bees, Biodiversity, Biogeography, Brazil, Evolution, Pollination

The evolution of pollination systems in one of the largest plant families: a new study just published – download it for free

Figure 1 JUNE revision

Interactions between flowering plants and the animals that pollinate them are known to be responsible for part of the tremendous diversity of the angiosperms, currently thought to number at least 350,000 species.  But the diversity of different types of pollination system (bird, bee, moth, fly, etc.) is unknown for most large, related groups of plants (what systematists term “clades”) such as families and subfamilies.  In addition we know little about how these interactions with pollinators have evolved over time and in different parts of the world.  Only a handful of groups of flowering plants have been studied with respect to questions such as:

How much do we currently know about the diversity of pollination systems in large clades?

How is that diversity partitioned between the smaller clades (e.g. subfamilies, tribes, genera) of a family, and what are the evolutionary transitions between the major groups of pollinators?

Do these pollination systems vary biogeographically across the clade’s range?

These sorts of questions have been addressed for the massive, globally distributed Apocynaceae (one of the top 10 or 11 largest angiosperm families with more than 5,300 species) in a study just published using a new database of pollinators of the family.  What’s more, the work is open access and anyone can download a copy for free.  Here’s the citation with a link to the paper:

Ollerton, J., Liede-Schumann, S., Endress, M E., Meve, U. et al. [75 authors in all] (2018) The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study. Annals of Botany (in press)

In this study we have shown that (among other things):

  • The family is characterised by an enormous diversity of pollination systems involving almost all of the major pollen vectors and some that are nearly unique to the Apocynaceae.
  • Earlier diverging clades have a narrower range of pollination systems than those that evolved later.
  • Transitions from one type of pollination system to another are evolutionarily constrained, and rarely or never occur, whereas others have taken place much more often, e.g. between wasp and beetle pollination.
  • There is significant convergent evolution of pollination systems, especially fly and moth pollination, by geographically and phylogenetically distinct clades.

You’ll notice that there are 75 (!) authors on this paper.  That’s because we’ve pulled together a huge amount of previously unpublished data and used some state of the art analyses to produce this work.  It was a monumental effort, especially considering that my colleague Sigrid Liede-Schumann and I only decided to push ahead with this project about a year ago when we chatted at the International Botanical Congress that I posted about at the timeIn truth however the origins of this paper go back over 20 years to 1997 when when Sigrid and I published a study of what was then known about pollination systems in the Asclepiadaceae (the asclepiads).

In that paper we said that the research “is intended to be ongoing…[we]…hope to re-review asclepiad pollination within the next decade”.  At the time I didn’t think it would actually take more than 20 years!  However over that period a lot has changed.  For one thing the Asclepiadaceae no longer exists, broken up and subsumed within a much larger Apocynaceae.  Also, I’ve done a lot of work in the field and in the herbarium on some of the smaller groups within the family, such as CeropegiaOthers, including many of my co-authors, have also been working on different groups in various parts of the world.  Finally the level of sophistication of the analyses we are now able to do has increased beyond recognition compared to what we could achieve in the mid-1990s.  All of this means that now is the right time to produce this study.

Having said all of that, this is still a work in progress.  Our Pollinators of Apocynaceae Database contains a sample of just over 10% of the species in the family.  So lots more data on plant-pollinator interactions needs to be collected before we say we fully understand how pollination systems have evolved in this most remarkable family.  I’d be happy to talk with anyone who is interested in the family and being involved in future data collection.

The database will be freely available to anyone who wants to use it – lots more can be done with this information and, once again, I’m happy to chat with potential collaborators.

I was recently interviewed about the study, and about plant-pollinator interactions and the Apocynaceae more generally, for the In Defense of Plants podcast – here’s a link to that interview.

Finally, I’d like to express my sincerest thanks to my co-authors on this study – I really couldn’t have done it without you guys!

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Filed under Apocynaceae, Biodiversity, Biogeography, Evolution, Pollination, Wasps

Speaking about plant-pollinator research and science blogging in Wageningen in May

Wageningen poster.jpg

If any of you are near Wageningen University on 31st May I’m giving a talk about some of our recent research called “The macroecology and macroevolution of plant-pollinator interactions”.  It’s preceded by a workshop on the whys and hows of science blogging.  Details are in the poster.

Here are the abstracts for the talk and the workshop:

Macroecology and macroevolution of plant-pollinator interactions

Plant-pollinator relationships are an ecologically critical form of interaction that ensures the long-term survival of the majority of the world’s plants species, and contribute to a large fraction of global agricultural output.  In additiondiversity and abundance of biotically pollinated plant species can be an important determinant of the diversity of animals at higher trophic levels.

Despite that global significance, most studies of plant-pollinator interactions are done at a local level, involving populations and communities of species, over modest time scales.  The ways in which these local sets of interactions scale up to produce global macroecological and macroevolutionary patterns, and the processes underpinning them, will be explored using two case studies.

The first is a data set of 67 plant communities, ranging from 70ºN to 34ºS, with which we investigated the roles of biotic and abiotic factors as determinants of the global variation in animal versus wind pollination.  Factors such as habitat type, species richness, insularity, topographic heterogeneity, current climate and late-Quaternary climate change were investigated. The predictive effects of these factors on the proportion of wind- and animal-pollinated plants were examined (see: Rech et al. 2016 – Plant Ecology & Diversity 9: 253-262).

Since these results were published  we have increased the number of plant communities in our database to >90, and our findings seem to be robust to these additional data.  The dominant influence of contemporary climate on the relative importance of wind-pollinated species suggests that communities may be sensitive to future climate change.  Communities in areas that are predicted to become drier may in time contain more wind-pollinated plants which may in turn reduce the diversity of pollinator species that are present.  There may also be implications for the prevalence of human pollen allergies.  Future work will focus on these two areas.

The second case study uses a newly assembled database of pollinators of the family Apocynaceae (one of the ten largest families of flowering plants), supported by a molecular phylogeny of the major clades.  This database has been used to explore phylogenetic and biogeographic patterns of pollinator exploitation (Ollerton et al. in review).  The findings from this study challenge some long-held assumptions about convergent evolution, the role of rewards such as nectar, and the notion that some specialised pollination systems are evolutionary “dead ends”.  It also highlights the function of novel floral features in determining pollinator type and behaviour, such as the fused gynostegium and pollinia found in the subfamily Asclepiadoideae.  In summary, Apocynaceae is emerging as an important model family for understanding the ecology and evolution of plant-pollinator interactions.

 

Blogging for EEB: why bother?

A growing number of scientists in Ecology and Evolutionary Biology (EEB) have their own blogs or post as guests on others’ blogs.  In this workshop we will explore motivations and strategies for blogging, and its advantages for early career researchers.  Why blog?  What does it do for one’s career?  Is it a distraction from actually doing science?  How does one build a blog readership?  We will also focus on two aspects that are sometimes seen as mutually exclusive: blogging as science outreach to the general public (sci-communication), versus blogging with other professional scientists in mind (sci-community).  As preparation for the seminar please read Saunders et al. (2017) Bringing ecology blogging into the scientific fold: measuring reach and impact of science community blogs

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Plant-pollinator networks in the tropics: a new review just published.

P1080615

As an ecologist who has carried out field work in the temperate zone (UK), the subtropics (Tenerife and South Africa) and the tropics (parts of South America, Africa and Australia)  I’ve always found the idea that the study of ecology can be divided into “tropical” and “non-tropical” a bit odd.  It’s as if the way that the natural world works somehow changes at about 23 degrees north or south of the equator, making things “different” around the equator.  The tropics are a very special, diverse place, it’s true, but so are many places outside the tropics.

With this in mind I was pleased when I was asked by some of my Brazilian colleagues to contribute to a chapter in a new book entitled Ecological Networks in the Tropics. It was an opportunity to review what is known about plant-pollinator networks in the tropics and the ways in which they are very similar to such networks at lower latitudes. Here’s the details of the chapter, followed by the abstract.  If anyone wants a copy please drop me an email:

Vizentin-Bugoni J, PKM Maruyama, CS Souza, J Ollerton, AR Rech, M Sazima. (2018) Plant-pollinator networks in the tropics: a review. pp 73-91 In Dáttilo W & V. Rico-Gray. Ecological networks in the Tropics. Springer.

Abstract:

Most tropical plants rely on animals for pollination, thus engaging in complex interaction networks. Here, we present a global overview of pollination networks and point out research gaps and emerging differences between tropical and non-tropical areas. Our review highlights an uneven global distribution of studies biased towards non-tropical areas. Moreover, within the tropics, there is a bias towards the Neotropical region where partial networks represent 70.1% of the published studies. Additionally, most networks sampled so far (95.6%) were assembled by inferring interactions by surveying plants (a phytocentric approach). These biases may limit accurate global comparisons of the structure and dynamics of tropical and non-tropical pollination networks. Noteworthy differences of tropical networks (in comparison to the non-tropical ones) include higher species richness which, in turn, promotes lower connectance but higher modularity due to both the higher diversity as well as the integration of more vertebrate pollinators. These interaction patterns are influenced by several ecological, evolutionary, and historical processes, and also sampling artifacts. We propose a neutral–niche continuum model for interactions in pollination systems. This is, arguably, supported by evidence that a high diversity of functional traits promotes greater importance of niche-based processes (i.e., forbidden links caused by morphological mismatching and phenological non-overlap) in determining which interactions occur, rather than random chance of encounter based on abundances (neutrality). We conclude by discussing the possible existence and direction of a latitudinal gradient of specialization in pollination networks.

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Local and regional specialization in plant–pollinator networks: a new study just published

Euphorbia canariensis pollinators 2016-04-29 17 58 00

A fundamental feature of the natural world is that no species exists in isolation: all organisms interact with other organisms during their lives. These interactions take many forms and the outcome varies with the type of interactions. For example predator-prey interactions are clearly negative for the prey species, but positive for the predator. Other interactions result in positive outcomes for both species, including relationships between pollinators such as bees, birds and flies, and the flowers that they pollinate. An important feature of such interactions is how specialized or generalized it is; that is, how many different pollinators are actually involved in pollinating a particular type of flower, or how many types of flower does a specific pollinator visits.

In a newly published study, I have collaborated with colleagues from Denmark and Brazil to assess how local specialization (within a community) relates to regional specialization (across communities) using two separate data sets from the Brazilian rupestrian grasslands and Canary Island/North African succulent scrub vegetation.

Here’s the citation with a link to the paper (drop me a line if you can’t access it and need a PDF):

Carstensen, D.W., Trøjelsgaard, K., Ollerton, J. and Morellato, L.P.C. (2017) Local and regional specialization in plant–pollinator networks. Oikos (in press) doi:10.1111/oik.04436

The abstract is as follows:

“Specialization of species is often studied in ecology but its quantification and meaning is disputed. More recently, ecological network analysis has been widely used as a tool to quantify specialization, but here its true meaning is also debated. However, irrespective of the tool used, the geographic scale at which specialization is measured remains central. Consequently, we use data sets of plant–pollinator networks from Brazil and the Canary Islands to explore specialization at local and regional scales. We ask how local specialization of a species is related to its regional specialization, and whether or not species tend to interact with a non-random set of partners in local communities. Local and regional specialization were strongly correlated around the 1:1 line, indicating that species conserve their specialization levels across spatial scales. Furthermore, most plants and pollinators also showed link conservatism repeatedly across local communities, and thus seem to be constrained in their fundamental niche. However, some species are more constrained than others, indicating true specialists. We argue that several geographically separated populations should be evaluated in order to provide a robust evaluation of species specialization.”

This is what those two different habitats look like:

If you would like more information on plant-pollinator networks, including details of an edible game for Christmas (!), follow this link to the standingoutinmyfield blog.

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Pollinator biodiversity and why it’s important: a new review just published – download it for free

P1110763

In a new review paper that’s just been published in the Annual Review of Ecology, Evolution and Systematics I have looked at the question of just how diverse the pollinators are, and why pollinator biodiversity is ecologically important and therefore worthy of conservation.  I’ve taken a deep time and wide space approach to this, starting with what the fossil record tells us about when animal pollination evolved and the types of organisms that acted as pollinators in the past (the answer may surprise you if you’re unfamiliar with the recent paleontological literature on this topic).  Some of the most prominent biogeographical patterns have been highlighted, and I have tried to estimate the global diversity of currently known pollinators.  A conclusion is that as many as 1 in 10 described animal species may act as pollen vectors.

As well as this descriptive part of the review I’ve summarised some recent literature on why pollinator diversity matters, and how losing that diversity can affect fruit and seed set in natural and agricultural contexts.  Extinction of pollinator species locally, regionally, and globally should concern us all.

Although I was initially a little worried that the review was too broad and unfocused, having re-read it I’m pleased that I decided to approach the topic in this way.  The research literature, public policy, and conservation efforts are currently moving at such a fast pace that I think it’s a good time to pause and look at the bigger picture of what “Saving the Pollinators” actually means and why it’s so important.  I hope you agree and I’d be happy to receive feedback.

You can download a PDF of the review entitled Pollinator Diversity: Distribution, Ecological Function, and Conservation by following that link.

Pollination ecologists should also note that in this same volume of Annual Review of Ecology, Evolution and Systematics there’s a review by Spencer Barrett and Lawrence Harder called The Ecology of Mating and Its Evolutionary Consequences in Seed Plants.  If you contact those authors I’m sure they’d let you have a copy.

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Filed under Apocynaceae, Bees, Biodiversity, Biogeography, Birds, Butterflies, Climate change, Ecosystem services, Evolution, Honey bees, Hoverflies, IPBES, Macroecology, Mammals, Moths, Mutualism, Neonicotinoids, Pollination, Urban biodiversity, Wasps

Who was the father of biogeography? Let poetry decide! UPDATED

Norway from the air.jpeg

Over at the Dynamic Ecology blog yesterday, Jeremy Fox posted in the weekly Friday Links feature a piece about clerihews – four line poems about an eminent individual that follows a strict AA BB rhyming structure.  Jeremy’s challenge of “+1000 Internet Points for anyone who writes a clerihew about an ecologist in the comments”, of course, was like a proverbial red rag.  The clerihews came rolling in, including some great contributions, and some dodgy rhymes…  I contributed a couple:

Darwin’s natural selection
Was received with circumspection
But with development of society
Evolution replaced piety

and

Following the theories of Darwin
Science and religion were a-warrin’
But after natural selection
Came more balanced introspection

But then I suddenly found myself in a clerihew face-off  with Brazilian ecologist Rafael Pinheiro, which is too good not to preserve for posterity:

RP:

Look to this poor man called Wallace
He was not born and raised in a palace
But don’t get fooled by this misleading photography
The man is the father of biogeography

JO:

Von Humboldt travelled and mapped plants
When schoolboy Wallace wore short pants
So in a more accurate historiography
Von Humboldt’s the father of biogeography

RP:

Humboldt came first, I will not deny
But Wallace is the father and I’ll tell you why
He was not the first to study species distribution
But the one who explained it through evolution

JO:

Sure, Hooker embraced Darwin’s evolution
And came up with a very modern conclusion
But fatherhood is not about interpretation
It’s about the initial insemination

Jeremy award us 10,000 Internet Points and we agreed to call it a draw 🙂  Thanks to Jeremy for the initial challenge and to Rafael for being such a good sport.  It was a lot of fun.

UPDATE:

Jeremy has also highlighted the contributed clerihews with this post on Dynamic Ecology, to which Rafael has commented:

Jeff Ollerton studied pollinators and plants
When graduateboy me read his papers wearing short pants
So, I must admit, I am happy to be the one
Who faced him in the first clerihew slam

To which there’s only one possible response:

Rafael Pinheiro it’s been my pleasure
To trade these clerihews at leisure
But your last one, truth be told
Makes me feel old

 

 

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How many trees are there in Amazonia: two recent studies reached very different conclusions – UPDATED

The region of South America that we know as “Amazonia” has arguably the greatest biological diversity of any part of the planet, certainly as far as plants are concerned.  In some places the number of tree species per hectare exceeds 400, an order of magnitude greater than the number for the whole of the British Isles.  However estimating the total number of even the described plant species in this vast area has proven controversial, as two recent studies exemplify.  The first study was by ter Steege et al. (2016) and entitled “The discovery of the Amazonian tree flora with an updated checklist of all known tree taxa“, whilst the second is from just last month: Cardoso et al. (2017) “Amazon plant diversity revealed by a taxonomically verified species list“.  Both of them are open access so click on the links if you want to read the full studies.

One might expect that two such studies focused on Amazonia, both using vouchered herbarium records, would reach broadly similar conclusions as to the number of tree species in the region.  Not a bit of it: ter Steege et al. (2016) report 11,676 species, whilst Cardoso et al. (2017) say that the figure is 6,727.  That’s almost a two-fold difference!  Why the discrepancy?  Inspired by an initial tweet by University of Glasgow taxonomist Roderic Page, I downloaded the data from both studies and looked at it closely.

Here’s a scatter plot of the number of tree species per plant family reported by both studies:

Amazon tree diversity

 

The red line shows where we would expect the data points to lie if both studies had reported the same number of tree species per family.  Clearly few families lie on this line and most are above it as we might expect: as I’ve said, ter Steege et al. (2016) concluded that there were far more tree species overall and this is reflected at the family level.  Note that I’ve graphed this using a log scale and what might seem to be small differences are actually very large indeed.

Although the findings from two studies are highly correlated (diverse families are diverse in both studies, ditto families with low diversity) the actual level of that species richness is very different.  For example, in the Annonaceae, ter Steege et al. report  480 species, Cardoso et al. report 388; in the Clusiaceae the figures are 247 versus 135.  Other families are excluded from one data set or the other: ter Steege et al. reckon there 7 species of trees in the Dilleniaceae whereas Cardoso et al. cite zero.  Here’s a link to the data set if you want to explore further.  

So what’s going on here?  Why do two studies with similar aims, published about 12 months apart, come to such different conclusions.  As far as I can see there are three reasons for this.

First of all, the studies used slightly different taxonomies when it came to considering families and species.  So for example, Cardoso et al. recognise the family Peraceae which ter Steege et al. do not.  Although I haven’t done it, I’m sure that if one were to dig down to the species level there would be differences in which species were accepted and which were considered synonyms.

Secondly, the exact definition of what constitutes a “tree” varies between botanists, and the non-botanists who are no doubt responsible for some of the plant collections: some consider anything to be woody and tall-ish to be a “tree”, others have more strict definitions.  Notes about growth form taken in the field consequently get included in herbarium databases and may be inaccurate, especially for the uncommon species that have rarely been seen in the field.

The final reason, and the one that seems to be responsible for most of the discrepancy, is the definition of what constitutes “Amazonia”.  In the first study ter Steege et al. defined it as including the “forests and savannahs of the Amazon basin and Guiana Shield”.  In contrast Cardoso et al. considered only “lowland Amazon rain forests”.  That’s a big difference as there’s lot of savannah in this region, as well as other habitat types.  When we did field work in Guyana some years ago we could travel very quickly between savannah and rainforest.  It was clear to us that there is a range of trees that are restricted to one habitat or another, including species of Dilleniaceae (mentioned above) that are savannah specialists (hence the family’s exclusion from the Cardoso et al. study).

Now neither of these studies is “wrong” in the sense of being inaccurate or misguided: both are great studies involving a huge effort on the part of the authors.  But the limitations and definitions of geography and taxonomy that I’ve highlighted do mean that they need to be treated as rather different and not directly comparable.

So how many tree species are there in Amazonia?  If we consider just the rainforest then it’s 6,727 (Cardoso et al. 2017).  If we consider all habitats in the region, including rainforest plus savannah etc., then the figure is 11,676 species (ter Steege et al. 2016).  One of the implications of this is that the non-rainforest “Amazonian” habitats collectively contain 4949 tree species.  Thus a large proportion of the diversity of the region is in habitats, such as savannah, which are less of a focus for conservation efforts and not as well known to the general public, but are at least as threatened by agriculture and mining as rainforest.

Thanks to Roderic Page for initially highlighting this on Twitter, and Sandy Knapp for discussion.

UPDATE:  In retrospect my conclusion above regarding the proportion of trees in non-lowland rainforest habitats was much too high, as a couple of commenters have noted below.  It’s worth reading what they have to say, and my responses.  It’s likely that the taxonomic differences between the two studies are at least as great as the geographical ones, but then taxonomic opinions vary hugely.  Just serves to emphasise what a controversial and problematic question this is!

 

 

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The macroecology of animal versus wind pollination – a new study just published

In collaboration with colleagues in Brazil, Denmark, and elsewhere in the UK, we’ve just published a new research paper which looks at the global spatial distribution of wind and animal pollinated plant species, and the underlying historical and contemporary ecological causes of that distribution.  It’s a study that builds on my “How many flowering plants are animal pollinated?” paper in Oikos, and has been a long time in its gestation.  We’re very excited by its findings and plan to develop this project in the future.

As a bonus we made the cover of the journal with the amazing image below!  Big thanks to Pedro Viana and Jesper Sonne for the photos.

Here’s the citation with a link to the publisher’s website; the abstract is below.  If anyone wants a PDF copy, please ask.

Rech AR, Dalsgaard B, Sandel B, Sonne J, Svenning J-C, Holmes N & Ollerton J (2016) The macroecology of animal versus wind pollination: ecological factors are more important than historical climate stability. Plant Ecology & Diversity 9: 253-262

 

Abstract:

Background: The relative frequency of wind- and animal-pollinated plants are non-randomly distributed across the globe and numerous hypotheses have been raised for the greater occurrence of wind pollination in some habitats and towards higher latitudes. To date, however, there has been no comprehensive global investigation of these hypotheses.

Aims: Investigating a range of hypotheses for the role of biotic and abiotic factors as determinants of the global variation in animal vs. wind pollination.

Methods: We analysed 67 plant communities ranging from 70º north to 34º south. For these we determined habitat type, species richness, insularity, topographic heterogeneity, current climate and late-Quaternary climate change. The predictive effects of these factors on the proportion of wind- and animal-pollinated plants were tested using correlations, ordinary least squares (OLS) and logistic regression analyses with information-theoretic model selection.

Results: The proportion of animal-pollinated plant species was positively associated with plant species richness and current temperature. Furthermore, in forest, animal pollination was positively related to precipitation. Historical climate was only weakly and idiosyncratically correlated with animal pollination.

Conclusion: Results were consistent with the hypothesised reduced chance for wind-transported pollen reaching conspecific flowers in species-rich communities, fewer constraints on nectar production in warm and wet habitats, and reduced relative effectiveness of wind dispersal in humid areas. There was little evidence of a legacy of historical climate change affecting these patterns.

andre-capa-1

 

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The integration of alien plants in mutualistic plant–hummingbird networks – a new study by Maruyama et al. (2016)

The collaborations with researchers in Brazil and Denmark in which I’ve been involved in recent years, focused particularly on hummingbirds and networks of plant pollinator interactions, have been very productive, most recently seen in a study of the effects of hummingbird feeders on diversity and abundance of the birds.

This collaboration continues with a new study that has just been published in the journal Diversity and Distributions which deals with the way in which non-native plant species are exploited by assemblages of hummingbirds in the New World.  Here’s the abstract:

 

Aim:  To investigate the role of alien plants in mutualistic plant–hummingbird networks, assessing the importance of species traits, floral abundance and insularity on alien plant integration.

Location: Mainland and insular Americas.

Methods: We used species-level network indices to assess the role of alien plants in 21 quantitative plant–hummingbird networks where alien plants occur. We then evaluated whether plant traits, including previous adaptations to bird pollination, and insularity predict these network roles. Additionally, for a subset of networks for which floral abundance data were available, we tested whether this relates to network roles. Finally, we tested the association between hummingbird traits and the probability of interaction with alien plants across the networks.

Results: Within the 21 networks, we identified 32 alien plant species and 352 native plant species. On average, alien plant species attracted more hummingbird species (i.e. aliens had a higher degree) and had a higher proportion of interactions across their hummingbird visitors than native plants (i.e. aliens had a higher species strength). At the same time, an average alien plant was visited more exclusively by certain hummingbird species (i.e. had a higher level of complementary specialization). Large alien plants and those occurring on islands had more evenly distributed interactions, thereby acting as connectors. Other evaluated plant traits and floral abundance were unimportant predictors of network roles. Short-billed hummingbirds had higher probability of including alien plants in their interactions than long-billed species.

Main conclusions: Once incorporated into plant-hummingbird networks, alien plants appear strongly integrated and, thus, may have a large influence on network dynamics. Plant traits and floral abundance were generally poor predictors of how well alien species are integrated. Short-billed hummingbirds, often characterized as functionally generalized pollinators, facilitate the integration of alien plants. Our results show that plant–hummingbird networks are open for invasion.

 

The full reference is: Maruyama, P.K. et al. (2016) The integration of alien plants in mutualistic plant–hummingbird networks across the Americas: the importance of species traits and insularity.  Diversity and Distributions (in press).

Happy to send a PDF to anyone who would like one.

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