Douglas W. Tallamy

Impact of Native Plants on Bird and Butterfly Biodiversity in Suburban Landscapes

Managed landscapes in which non-native ornamental plants are favored over native vegetation now dominate the United States, particularly east of the Mississippi River. We measured how landscaping with native plants affects the avian and lepidopteran communities on 6 pairs of suburban properties in southeastern Pennsylvania. One property in each pair was landscaped entirely with native plants and the other exhibited a more conventional suburban mixture of plants--a native canopy with non-native groundcover and shrubs. Vegetation sampling confirmed that total plant cover and plant diversity did not differ between treatments, but non-native plant cover was greater on the conventional sites and native plant cover was greater on the native sites. Several avian (abundance, species richness, biomass, and breeding-bird abundance) and larval lepidopteran (abundance and species richness) community parameters were measured from June 2006 to August 2006. Native properties supported significantly more caterpillars and caterpillar species and significantly greater bird abundance, diversity, species richness, biomass, and breeding pairs of native species. Of particular importance is that bird species of regional conservation concern were 8 times more abundant and significantly more diverse on native properties. In our study area, native landscaping positively influenced the avian and lepidopteran carrying capacity of suburbia and provided a mechanism for reducing biodiversity losses in human-dominated landscapes.

Insect Parental Care

The evolution of parental care represents an extraordinary breakthrough in the adaptation of organisms to their environment. Its effectiveness in neutralizing conditions harmful to young is attested by the repeated convergence of parental behavior patterns throughout vastly different animal lineages. Parental care is an important life history trait in many crustaceans, myriopods, arachnids, and insects in addition to mammals, birds, reptiles, amphibians, and fish. A considerable body of theory has been developed to explain such parent-offspring interactions as the timing and degree of parental investment (Emlen 1970, Milinski 1980, Williams 1966), selfish conflicts that arise between parents and their young (Trivers 1974), and sexual differences in parental care (Maynard Smith 1977, Trivers 1972). Until recently, however, widespread ignorance of invertebrate social systems has almost exclusively restricted the testing of these theories to vertebrates.

Squash Beetle Feeding Behavior: An Adaptation against Induced Cucurbit Defenses

This study tests the hypothesis that feeding behavior in the herbivorous coccinellid Epilachna borealis is an effective adaptation for avoiding facultative chemical defenses in its cucurbit host plants. Chemical analyses, feeding preference tests, fitness evaluations, and cucumber beetle assays for cucurbitacins show that (1) beetle feeding damage to zucchini leaves triggers chemical change in damaged leaves and leaves adjacent to damaged leaves; (2) this change in leaf chemistry is sufficiently potent for beetles to detect and avoid; (3) induced changes in leaf chemistry negatively affect E. borealis fitness; (4) E. borealis trenching behavior blocks, at least temporarily, the translocation of cucurbitacin defenses to feeding sites, thus preserving the palatability and quality of food resources for beetles.

Maternal care in Gargaphia solani (Hemiptera: Tingidae)

We investigated the extent to which maternal behaviour exists in the lacebug Gargaphia solani as well as the adaptive relevance of maternal behaviour to predation, interspecific competition, feeding facilitation, and environmental heterogeneity. G. solani females aggressively defend their progeny against predators until maturity but provide no assistance in feeding, aggregating, or locating resources. In the absence of predators, nymphs suffer no ill effects if raised without their mother, but when nymphs are orphaned in normal field conditions only 3% survive to maturity. Such strong selection has given rise to maternal defensive behaviour that enables Gargaphia females to defend their progeny against predators.

Polymorphism in Plant Defense Against Herbivory: Constitutive and Induced Resistance in Cucumis sativus

Theory predicts that plant resistance to herbivores is determined by both genetic and environmentally induced components. In this study, we demonstrate that the phenotypic expression of plant resistance to spider mite herbivory in Cucumis sativus is determined by genetic and environmental factors and that there is an interaction between these factors. Previous feeding by spider mites induced systemic resistance to subsequent attack over several spatial scales within plants, reducing the population growth of mites compared to that on control plants. Effects of induction were effective locally over the short term, but resulted in local increased susceptibility to spider mite attack after several days. However, this local induced susceptibility on the damaged leaf was associated with induced resistance on newer leaves. Induced resistance was correlated with increases in cucurbitacin content of leaves, but was not associated with changes in the density of leaf trichomes. Induced resistance to herbivory was not detected in plants of a genotype lacking constitutive expression of cucurbitacins, which were in general highly susceptibile to mite attack. Allocation trade-offs between growth and defense are often invoked to explain the maintenance of variation in the levels of plant resistance. Contrary to current thinking, neither constitutive nor herbivore-induced plant resistance were associated with reductions in plant allocation to root and shoot growth. However, plants that had high levels of induced resistance to spider mites were the most susceptible to attack by a specialist beetle. Such ecological trade-offs between resistance to generalist herbivores and susceptibility to specialist herbivores may be important in the maintenance of variation of plant resistance traits. In summary, C. sativus exhibits strong genetic variation for constitutive and induced resistance to spider mites, and this variation in resistance is associated with ecological trade-offs.

Courtship role reversal and deceptive signals in the long-tailed dance fly, Rhamphomyia longicauda

We examined the function of secondary sexual characters in the role-reversed, lekking behaviour of female long-tailed dance flies, Rhamphomyia longicauda Loew (Empididae), to test the hypothesis that the degree of abdominal distention is an honest female signal about the state of egg development. Female Rhamphomyia cannot hunt for prey and they receive all of their protein from males by exchanging copulations for nuptial prey gifts. Females compete for male gifts within leks that are organized for a brief period each evening before dark. Before hovering within leks, females swallow air, inflating expandable pouches on the pleural margins of the abdomen. The result is a large saucer-like abdomen which is further exaggerated by wrapping scaled pro-, meso- and metathoracic legs along its pleural margins. Male preference for an enlarged abdomen was confirmed by suspending plastic models of varying size from monofilament lines and recording which models attracted the most males. There was a positive relationship between egg development and abdominal distention in a related species, R. sociabilis (Williston), which lacks inflatable abdominal pouches. Multiple regression showed that in R. longicauda, abdominal inflation completely masks the state of egg development. We conclude that female R. longicauda deceive mate-seeking males with the unreliable message that eggs are nearing maturation in order to obtain a protein meal in exchange for copulation. Males that fail to identify a female bearing mature eggs risk near-certain cuckoldry and an increased probability that the female will die before oviposition. Copyright 2000 The Association for the Study of Animal Behaviour.

Ranking lepidopteran use of native versus introduced plants.

In light of the wide-scale replacement of native plants in North America with introduced, invasive species and noninvasive ornamental plants that evolved elsewhere, we compared the value of native and introduced plants in terms of their ability to serve as host plants for Lepidoptera. Insect herbivores such as Lepidoptera larvae are critically important components of terrestrial food webs and any reduction in their biomass or diversity due to the loss of acceptable host plants is predicted to reduce the production of the many insectivores in higher trophic levels. We conducted an exhaustive search of host records in the literature. We used the data we gathered to rank all 1385 plant genera that occur in the mid-Atlantic states of the United States by their ability to support Lepidoptera richness. Statistical comparisons were made with Welchs test for equality of means. Woody plants supported more species of moths and butterflies than herbaceous plants, native plants supported more species than introduced plants, and native woody plants with ornamental value supported more Lepidoptera species than introduced woody ornamentals. All these differences were highly significant. Our rankings provide a relative measure that will be useful for restoration ecologists, landscape architects and designers, land managers, and landowners who wish to raise the carrying capacity of particular areas by selecting plants with the greatest capacity for supporting biodiversity.

Migration in Heterogeneous Environments: Differences in Habitat Selection Between the Wing Forms of the Dimorphic Planthopper, Prokelisia Marginata (Homoptera: Delphacidae)

The planthopper, Proklisia marginata, feeds selectively on the intertidal grass, Spartina alterniflora. Populations contain two adult wing forms that vary in proportion from one local area to the next. There are short—winged flightless individual (brachypters) and individuals with fully developed wings (macropters) that fly. Differences in the ability of the two wing forms to select high quality habitats in a heterogeneous environment are measured to elucidate further the advantages of migration (macroptery). Adult planthoppers (both wing forms) occur most abundantly on the parts of individual plants, seed heads in particular, that contain the highest percent crude protein. The percent crude protein in stands of S. alterniflora and the frequency of flowering plants are used as measures of habitat quality and vary considerably over the marsh surface. There is a significant positive relationship between the densities of both wing forms and habitat quality. However, the slope of the regression line for macropters is significantly steeper than for brachypters suggesting that macropters are better able to move from low— to high—quality patches. The relative mobility of wing forms is further documented by the inability of brachypters to colonize small defaunated plots of grass compared to macropters. We suggest variation in habitat quality is unpredictable, that high—quality patches of vegetation may be separated by distances greater than the ambit of brachypters, and that macropters can more effectively track spatial oscillations in habitat quality.

Copulatory courtship signals male genetic quality in cucumber beetles

In the spotted cucumber beetle, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae), males court females during copulation by stroking them with their antennae. Stroking occurs exclusively during the first stages of copulation, after a male has penetrated a females vaginal duct but before he is allowed access to her bursa copulatrix. Females accept the spermatophore of fast–stroking males and reject those of slow–stroking males by relaxing or constricting muscles distorting the vaginal duct. Here, we measure the repeatability of stroking behaviour within males, examine the effect of losing one antenna on male attractiveness and test whether such female control results in direct phenotypic benefits for the discriminating female or indirect genetic benefits that appear in her offspring. We also use a half–sibling design to quantify the variance and heritability of stroking speed and endurance. Female beetles were paired with a male that was known to stroke either quickly or slowly. No difference was found in the resulting fecundity or egg–hatching rate of the females, or in the survivorship, development rate, size, age at first reproduction or fecundity of their offspring indicating that no direct benefits are gained by discriminating among males on the basis of stroking speed. There were, however, good–genes benefits for the mates of fast–stroking males. Offspring of fast–stroking fathers were also fast strokers and were more likely to be accepted as mates than offspring of slow–stroking fathers. There was substantial variance among sires in stroking speed and endurance and the heritability of each trait was high. The antennal stroking rate was highly repeatable in successive mating attempts and males with only one antenna were not accepted as mates. The repeatability within males, variability between males and heritability between generations of copulatory stroking combine to provide females with a reliable and honest signal of the genetic quality of courting males.

Non‐native plants reduce abundance, richness, and host specialization in lepidopteran communities

The impact of non-native plant invasions on ecosystems has been controversial because obvious local effects have not yet led to the global extinction of any native plant species on continents and large islands. We suggest that extinction is not the appropriate measure of impact on ecosystem function and present evidence that non-native plant invasions or the replacement of native plants with non-native ornamentals results in significant bottom-up reductions of energy available for local food webs. Using replicated common gardens we compared Lepidoptera species richness and abundance on native plants, non-native congeners of those natives, and non-native species with no close relatives in the study area. Non-native plants supported significantly fewer caterpillars of significantly fewer specialist and generalist species even when the non-natives were close relatives of native host plants. However, the effect size was smaller in the latter category indicating phylogenetic similarity to local natives may pos...