Plant-Animal Interactions: An Evolutionary Approach (1)

“This book, aimed at upper-division undergraduate students and those starting graduate studies, attempts to provide a manageable synthesis of recent developments in the field of terrestrial plant-animal interactions”, they write in the introduction. One of the amazon reviewers claimed that “This is a VERY easy read” – which was actually, in combination with the high ratings it’s got, a large factor leading me to give this book a try; I figured that I shouldn’t be too worried about the fact that this book is written for advanced undergraduates/graduate students in a field I’m not super familiar with.

The book is actually not terribly difficult to read – in the sense that most concepts/terms applied throughout the book are defined along the way, meaning that you’re unlikely to have major issues understanding what’s going on even if you’re not an evolutionary biologist (I’m not, so I should know). It also helps that many of the terms which are not defined along the way will be sort of obvious to you from the context (they never really tell you what coprolite is, but I should think a picture of a dinosaur turd would help… I incidentally read about those things last year, so that particular word did not cause me problems). Although not all ‘potentially problematic terms’ are defined in the book most of them are, and there are a lot of definitions in this book. It’s quite dense; it’s a book where my average reading speed will be around 10 pages per hour, when measured over multiple hours and including necessary reading breaks and so on – perhaps 13-15 when things are going really well. I recently started reading Christie’s Peril at End House, and I’m reasonably sure it’ll take me less time to read that entire book than it took me reading chapter 2 of this book (chapter 2 was, I should perhaps add, significantly longer than the average chapter). I’m well aware that some textbooks are worse than 10-15 pages/hour and I have my eyes on another text dealing with related stuff which I’m reasonably sure will be a bit more work than this one was, and I’m also aware that some books catering to a more advanced audience will presumably take familiarity with many of the terms defined in this book for granted; but even so, calling this ‘a very easy read’ is perhaps a bit much. I should note that although I don’t want to delude anyone into thinking this book is easier to read than it is, I also really don’t want to give people reading along here more excuses not to read this book than is strictly necessary, because I think it’s just a great book.

I have decided to give the book a couple of posts here on the blog, perhaps 3, but I don’t know when I’ll post the others – I have finished the book, and I’ve started reading Kuhn. I’m somewhat behind on the book blogging at the moment, which tends to happen when I’m reading stuff offline; in part because blogging books I’ve read offline is in general a lot more work, among other things because I can’t copy/paste relevant segments when quoting from the books.

I’ve given the book five stars on goodreads simply because as mentioned it’s a really great book – it’s the sort of book which does all those things I’ve been consistently annoyed about popular science books dealing with topics related to the ones covered in this book not doing, and it’s on the other hand also the sort of book which does none of those annoying things the other type of books tend to do. The book doesn’t spend a page talking about how butterflies look nice, ‘you could see the sun setting in the distance…’, or some anecdote about the uncle of the author or crap like that; you have definitions, functional relationships and dynamics explored in detail – a thoroughly analytical approach, without all the infuriating crud. Occasional appreciation, yes, but mainly just the data, the dynamics, the science.

In biology you have two major fields called zoology (dealing with animals) and botany (dealing with plants), but “the knowledge of these two groups of organisms has traditionally progressed along separate lanes, under the leadership of different researchers and independently of each other” (a quote from the introduction). What this means is that there haven’t been a lot of people who’ve done work on ‘the stuff in the middle’ – which is a shame, as “we will never fully understand the evolution of the morphology, behaviour and life history of plants and animals unless we understand in sufficient detail their reciprocal influences in ecological and evolutionary time” (another quote from the introduction). So they’ve written down some of the things they know about these things. The book has nine chapters written by 13 different contributors. The first two chapters are sort of ‘general’ chapters; the first one is about: ‘Species interactions and the evolution of biodiversity’, and the second (much longer) one is about: ‘The history of associations between plants and animals’. In part 2 of the book, dealing with ‘mostly antagonisms’, they talk about plant-insect interactions (chapter 3), mammalian herbivory (chapter 4) and granivory (chapter 5 – “Granivory describes the interaction between plants and the animals (termed granivores or seed-predators) that feed mainly or exclusively on seeds.”). In part 3, dealing with ‘mostly mutualisms’, they talk about pollination by animals (chapter 6) and seed dispersal by vertebrates (chapter 7). In the last part, ‘synthesis’, they talk about ant-plant interactions (chapter 8) and a little bit about ‘future directions’ in research on these matters (chapter 9). In my opinion there were no bad chapters in this book – this is a ‘pure’ five star rating, without any kind of ‘compensatory stuff’ going on. Other people may disagree, but my opinion is that the book is well written, deals with super interesting stuff, and that this stuff is just plain fascinating!

It would be easy to write one post dealing with each of the chapters but I’m not going to do that, and so my posts about this book are going to be another set of those posts where you’ll spend perhaps 10-15 minutes on perhaps 10 hours of material. The book has a lot of stuff I simply cannot cover here, and I highly recommend that you read it if you find the stuff I cover here interesting. It’s been hard to blog this book because it’s in general really difficult to know what to exclude, and very easy to find new things to add. The stuff below covers some of the material from the first two chapters, corresponding to roughly 75 pages.

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“The majority of terrestrial organisms fly. […] The evolution of propelled and passive flight, and their consequences, may well be regarded as the most creative force in the development of biodiversity. Most plants fly at one stage of their life cycle or another, as pollen or as seeds or both. Spores of ferns and fungi fly. Pollen, spores and seeds are carried on the wind by a multitude of winged animals: insects, birds, bats and perhaps pterosaurs in their day. […] the vast majority of terrestrial organisms exist in trophic systems based on plants, be they the plant themselves, herbivores, carnivores, pollinators, frugivores or granivores […] as we climb the trophic ladder, species richness increases by orders of magnitude. A plant species, such as an oak, birch or willow, may be host to 200-300 insect herbivore species. Each herbivorous insect may be utilized by 10-20 carnivores, either predators or parasites. The plant provides both food and habitat for the associated fauna and many microhabitats are available for colonization […] Including undescribed species, there may be 10-100 million species of all kinds living today, over half of them insects, of which 99,5% can fly in the adult stage. […] Add to the insects about 9000 species of birds and 1000 bat species, together making up 80% of the warm-blooded vertebrates, and we see that conquest of the air has been an evolutionary ‘success’ of extreme proportions.”

“The basis for the spectacular radiations of animals on earth today is clearly the resources provided by the plants. They are the major primary producers, autotrophically energizing planet Earth. […] Well over 90% of energy in terrestrial systems is fixed by autotrophic plants (the remainder by algae and bacteria), and almost all terrestrial animals depend on autotrophic production, either directly as herbivores or saprophages, or for shelter and microhabitats, or indirectly as predators and parasites utilizing the second trophic level of herbivores. […] plant-animal interactions are both direct and indirect and ramify throughout the trophic system. […] multitrophic-level interactions are ubiquitous and important both for the understanding of natural interactions and for effective management of landscapes dominated by humans […] while plant hosts and their varied insect herbivores evolve and are constantly replaced in time and space, their associations nonetheless remain constant. A Paleozoic palaeodictyopterid insect imbibing vascular tissue sap from a marattialean tree fern is functionally playing the same role as an aphic today feeding on the same tissues in an angiosperm […] Given the taxonomic turnover of vascular plants and herbivorous insects and yet the survival of persistent ecological associations, the phenomenon of ecological convergence is an important long-term pattern […] multidisciplinary evidence from various geological disciplines, particularly those applied to the earlier part of the fossil record, indicate that the more ancient the ecosystem, the less it resembles the present.”

“Three hypotheses have been proposed for assessing how ecological units, such as functional feeding groups, dietary guilds and mouthpart classes, expand in macroevolutionary time […] The first hypothesis, the ecological saturation hypothesis (ESH), advocated by palaeobiologists, maintains that the total number of ecological positions, or roles, has remained approximately constant through time after an initial exponential rise […] Thus taxa enter and exit the ecological arena of the biological community […], but their associations or roles remain virtually level. By contrast, the expanding resource hypothesis (ERH) is favoured by biologists and states that there is a gradual increase in food resources and availability of niches through time […] the intrinsic trend of diversification hypothesis (ITDH) […] holds that the long-term patterns of ESH and ERH vary among groups of organisms […] This view would imply that the proportion of occupied ecological roles has a globally disjunct pattern according to group, time and space. Of these, the current data favors ESH, if one assumes that the ecological clock was set during the Pennsylvanian and the previous fossil record is too poor for analysis.”

“Taphonomy is the study of the physical, chemical and biotic events that affect organisms after death, including pre-burial processes that transform the original living community into an entombed death assemblage that may be encountered by paleobiologists many aeons later. The fidelity to which the preserved assemblage actually resembles the source community is an issue in dicussions of the quality of the fossil record […] A full appreciation of the fossil associational record [between insects and plants] requires an evaluation of the five major types of qualitative evidence: plant reproductive biology, plant damage, dispersed coprolites, gut contents, and insect mouthparts. […] Collectively, these five types of evidence range from the direct, ‘smoking gun’ of gut contents, where the consumer and consumed are typically identifiable, to the more remote and circumstantial evidence of floral reproductive biology and mouthparts, where inferences are based on functional understanding, usually from modern analogues. […] Of all types of evidence for plant-arthropod associations, plant damage has the most extensive fossil record […] gut contents are the rarest type of evidence for plant-animal associations”

“Functional feeding groups can be sorted into 14 basic ways that insects access food” [I had no idea! And yes, they talk about all of these in the book. Note that you can easily split up those ‘basic ways’ into more subcategories if you like:] “In well-preserved Cretaceous and Caenozoic angiosperm-dominated floras, there are approximately 30 distinct types of external foliage-feeding, ranging from generalized bite-marks on margins to highly stereotyped and often intricate patterns of slot-hole feeding: earlier floras have fewer recognizable types of damage. […] The history of arthropod feeding on plants began during the Late Silurian to early Devonian […] by the close of the Pennsylvanian, the expansion of arthropod herbivory had invaded all plant organisms and virtually all plant tissues […] This expansion of dietary breadth provided a modern cast to the spectrum of insect diets. […] while the overwhelming bulk of the 14 plant-associated diet types was in place during the late Pennsylvanian, it was followed by the addition of 4 novel diet types during the Mesozoic in conjunction with the establishment of freshwater ecosystems and the diversification of advanced seed plants. […] When expressed as a diversity curve spanning the past 400 million years, there is a linear but stepped rise in mouthpart class diversity from the Early Devonian to the Early Jurassic, where it reached a plateau, followed by only a few subsequent additions […] Thus virtually all basic mouthpart innovation, including plant-associated mouthpart classes, was established prior to the angiosperm ecological expansion during the Middle Cretaceous [this was when flowering plants really took off, US], suggesting that mouthpart classes are attributable to basic associations with seed plants, or vascular plants of the more remote past, rather than the relatively late-appearing angiosperms […] Arthropods have used plants extensively for shelter probably since the Early Devonian”

“The amount of live plant tissue assimilated by arthropods is significantly greater than that of vertebrates in virtually all biomes except grasslands […] The fossil evidence indicates that this arthropod dominance has probably been the case since the establishment of the earliest terrestrial ecosystems. In fact, it was not until the latest Devonian that vertebrates emerged on land […], for which evidence indicates obligate carnivory. […] Direct evidence for vertebrate herbivory does not occur until the latest Pennsylvanian to earliest Permian […], about 100 million years after it appeared among mid-Paleozoic arthropods. […] A consequence of large vertebrate size is that consumption of plant organs is frequently complete and not partial as it is among arthropods, leaving minimal evidence from leaves, seeds and other wholly-consumed items. Also, the rarity of vertebrates when compared to arthropods may result in an underestimate of vertebrate importance in their interactions with plants. […] An interesting aspect of Paleozoic tetrapod herbivores is that they were uniformly short-necked and short-limbed browsers that cropped plant material within a metre to perhaps two metres of the ground surface. This trend continued […] into the Late Triassic, at which time basal dinosaur lineages began their diversification into virtually all major terrestrial feeding niches […] While Paleocene to middle Eocene mammalian herbivores were dominated by small to medium-sized forms consuming fruit, seeds and leaves, later herbivores were much larger, and invaded the browsing and eventually grazing adaptive zones […] This shift is related to the mid-Caenozoic origin of savanna and grassland biomes concomitant with the ecological spread of grasses. The oldest grasses reliably documented in the fossil record occur at the Palaeocene/Eocene boundary [~56 mya, US] […], although the earliest evidence for a grassland-adapted mammalian fauna is from the middle Oligocene [~28 mya, US] of Mongolia […] During the Pleistocene (2.65 Ma to 10 000 yr BP), much of the Planet underwent severe climactic pertubations from five major episodes of continental and associated alpine glaciation. Continental faunas were considerably reorganized during and after this interval in terms of dominance and composition of species […] Much evidence now supports a view that continental species did not respond as cohesive assemblages to these major environmental shifts, but rather individualistically […] An important exception to this trend are insects with high host specificity, which responded differently, retaining ancestral plant associations to the present […] or becoming extinct. Herbivorous mammals have less obligate dependence on plant species […] and thus exhibit greater dietary flexibility during times of major environmental stress.”