One of the least understood aspects of population biology is community evolution-the evolutionary interactions found among different kinds or organisms where exchange of genetic information among the kinds is assumed to be minimal or absent. Studies of community evolution have, in general, tended to be narrow in scope and to ignore the reciprocal aspects of these interactions. Indeed, one group of organisms is all too often viewed'as a kind of physical constant. In an extreme example a parasitologist might not consider the evolutionary history and responses of hosts, while a specialist in vertebrates might assume species of vertebrate parasites to be invariate entities. This viewpoint is one factor in the general lack of progress toward the understanding of organic diversification. One approach to what we would like to call coevolution is the examination of patterns of interaction between two major groups of organisms with a close and evident ecological relationship, such as plants and herbivores. The considerable amount of information available about butterflies and their food plants make them particularly suitable for these investigations. Further, recent detailed investigations have provided a relatively firm basis for statements about the phenetic relationships of the various higher groups of Papilionoidea (Ehrlich, 1958, and unpubl.). It should, however, be remembered that we are considering the butterflies as a model. They are only one of the many groups of herbivorous organisms coevolving with plants. In this paper, we shall investigate the relationship between butterflies and their food

/pdf/butterflies-and-plants-a-study-in-coevolution-59gysvp1oi.pdf

Butterflies and plants: a study in coevolution

Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...

https://www.jstor.org/stable/pdfplus/2830650.pdf

The dilemma of plants: To grow or defend.

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Infectious diseases can cause rapid population declines or species extinctions. Many pathogens of terrestrial and marine taxa are sensitive to temperature, rainfall, and humidity, creating synergisms that could affect biodiversity. Climate warming can increase pathogen development and survival rates, disease transmission, and host susceptibility. Although most host-parasite systems are predicted to experience more frequent or severe disease impacts with warming, a subset of pathogens might decline

/pdf/climate-warming-and-disease-risks-for-terrestrial-and-marine-gttfcx5ulf.pdf

Climate Warming and Disease Risks for Terrestrial and Marine Biota

Two features characterize all natural communities. First, they are dynamic systems. The densities and age-structures of populations change with time, as do the relative abundances of species; local extinctions are commonplace (37). For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated (36). The idea that equilibrium is rarely achieved on the local scale was expressed decades ago by a number of forest ecologists (e.g. 10 1, 168). One might even argue that continued application of the concept of climax to natural systems is simply an exercise in metaphysics (41). While this view may seem extreme, major climatic shifts often recur at time intervals shorter than that required for a community to reach competitive equilibrium or alter the geographical distributions of species (6, 21, 43, 76, 92). Climatic variation of this kind influences ecological patterns over large areas, sometimes encompassing entire continents. Other agents of temporal change in natural communities operate over a wide range of smaller spatial scales (47, 242). Second, natural communities are spatially heterogeneous. This statement is true at any scale of resolution (242), but it is especially apparent on what is commonly referred to as the regional scale. (By region I mean an area that potentially encompasses more than one colonizable patch.) Across any land or seascape, one observes a mosaic of patches identified by spatial discontinuities in the distributions of populations (153, 159, 161, 231, 239, 240). Closer examination often reveals a smaller-scale patchwork of same-aged individuals (e.g. 85-87, 101, 146, 199,204,217-220,235,246). Discrete patch boundaries sometimes reflect species-specific responses to

The Role of Disturbance in Natural Communities

We have verified that wild birds can become conditioned to reject naturally toxic insects either visually (experiment 1) or by taste (experiment 2). We have also verified, however, that unconditioned taste rejection of noxious chemicals by wild birds also occurs (experiment 3). Such unconditioned responses to the aposematic visual and taste cues of many insects, in fact, often appear to be as important as, or more important than, conditioned responses. In a large number of laboratory feeding experiments with wild birds as predators of aposematic insects, initial and/or long-term rejection occurs without prior laboratory conditioning experience. Although in some experiments the birds may have previously been exposed to (and therefore perhaps conditioned by) the aposematic prey in the wild, other experiments have used naive birds or insects whose ranges do not overlap those of the birds. Wiklund and Jarvi, for example, tested the response of 47 naive hand-raised birds of four species to five aposematic insect species, and found that 69/136 (51%) insects were rejected visually without even tasting, while 63 were tasted and then rejected. Only four of the insects were actually ingested. Similarly, in Bowers' study of the response of Massachusetts blue jays to aposematic western U.S. Euphydryas butterflies, several blue jays consistently rejected the butterflies visually or by taste without having eaten any. While these studies were not designed to separate neophobic effects from innate visual and/or taste aversions, they do differentiate between conditioned and unconditioned responses. Since both conditioned and unconditioned rejections can be demonstrated in the lab by insectivorous birds, and our available field evidence does not yet let us distinguish the mechanisms behind the observed patterns, our initial question, of the relative importance of conditioned versus unconditioned rejection mechanisms in different natural situations, is not yet answerable. The most important requirement of a food-rejection strategy is that it prevents both poisoning and starvation. We have shown, however, that rejection of a noxious insect by a bird can take place at four distinct levels (visual, non-destructive taste sampling, destructive taste sampling, or post-ingestional physiological rejection), the first three of which may be either unconditioned or conditioned by a physiological reaction to ingestion.(ABSTRACT TRUNCATED AT 400 WORDS)

A Natural Toxic Defense System: Cardenolides in Butterflies versus Birdsa

During their 5-mo overwintering period in Mexico, tens of millions of monarch butterflies (Danaus plexippus) form dense aggregations in forests dominated by oyamel fir trees (Abies religiosa). These forests provide a cool, moist environment that most monarchs use to maintain a state of reproductive diapause and to remain largely inactive until March, when they migrate back to the southern United States. In 1986, the Mexican government created the Monarch Butterfly Special Biosphere Reserve (MBSBR), but it is under pressure to allow forest extractions from core areas of the reserve. A recent argument to justify logging maintains that tree extraction would benefit monarchs by creating forest openings in which more plants would flower. The increased availability of nectar might mean that fewer monarchs would deplete their lipid contents, and therefore, more monarchs would survive the overwintering period. We investigated this hypothesis by comparing, throughout the overwintering period, lipid utilization and...

Use of lipid reserves by monarch butterflies overwintering in mexico: implications for conservation

DEFENSIVE mimicry has long been a paradigm of adaptive evolution by natural selection1–3. Mimics, models and predators in a batesian mimicry system (unpalatable model, palatable mimic) exist in a very different selective milieu from those in a mullerian system (involving ≳2 unpalatable 'co-models')1,4–6. Consequently, the incorrect characterization of a mimicry relationship obscures the natural histories of populations involved and undermines attempts to test general mimicry theory by means of empirical studies of specific systems. Here, we reassess the classic case of mimicry involving viceroy butterflies, Limenitis archippus (Cramer) (Nymphalidae), and two species they purportedly mimic: the monarch, Danaus plexippus (L.), and the queen, Danaus gilippus (Cramer) (Nymphalidae: Danainae). Viceroys are historically considered palatable (batesian) mimics7,8 of the chemically defended9 danaines. Our experiment refutes this interpretation by revealing that viceroys are as unpalatable as monarchs, and significantly more unpalatable than queens from representative Florida populations. This implies that viceroys are mullerian co-mimics of the danaines and prompts a comprehensive reassessment of this widely cited exemplar of mimicry.

The viceroy butterfly is not a batesian mimic

THE adaptive strategy of sequestering cardiac glycosides from milkweed plants (Asclepiadaceae and Apocynaceae) has evolved in several taxa of insects1. Since these cardenolides elicit vomiting following ingestion, birds learn to avoid the insects on sight after one or more emetic experiences2. By a specific assay, we found a spectrum of cardenolide concentrations in adult monarch butterflies (Danaus plexippus L., Danainae) collected during the autumnal migration from four areas in eastern North America3. In this communication we compare Atlantic with Pacific Coast monarch populations and explore quantitative relationships between cardenolide concentrations and palatability spectra. The latter were measured by our blue jay (Cyanocitta cristata bromia Oberholser, Corvidae) emetic dose fifty (ED50) test4.

Palatability dynamics of cardenolides in the monarch butterfly.

Root, stem, leaf, and latex samples ofAsclepias eriocarpa collected from three plots in one population at 12 monthly intervals were assayed for total cardenolide content by spectroassay and for individual cardenolides by thin-layer chromatography From May to September mean milligram equivalents of digitoxin per gram of dried plant were: latices, 568 ≫ stems, 612 > leaves, 40 > roots, 25 With the exception of the roots, significant changes in gross cardenolide content occurred for each sample type with time of collection during the growing season, whereas variation within this population was found to be small Labriformin, a nitrogen-containing cardenolide of low polarity, predominated in the latices Leaf samples contained labriformin, labriformidin, desglucosyrioside, and other unidentified cardenolides In addition to most of the same cardenolides as the leaves, the stems also contained uzarigenin The roots contained desglucosyrioside and several polar cardenolides The results are compared with those for other cardenolide-containing plants, and discussed in relation to anti-herbivore defense based on plant cardenolide content Arguments are advanced for a central role of the latex in cardenolide storage and deployment which maximizes the defensive qualities of the cardenolides while preventing toxicity to the plant

Lincoln P. Brower

Papers

A Natural Toxic Defense System: Cardenolides in Butterflies versus Birdsa

Use of lipid reserves by monarch butterflies overwintering in mexico: implications for conservation

The viceroy butterfly is not a batesian mimic

Palatability dynamics of cardenolides in the monarch butterfly.

Seasonal and intraplant variation of cardenolide content in the California milkweed,Asclepias eriocarpa, and implications for plant defense.