Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

The tolerance of plants to herbivory reflects the degree to which a plant can regrow and reproduce after damage from herbivores. Autoecological factors, as well as the influence of competitors and mutualists, affect the level of plant tolerance. Recent work indicates that there is a heritable basis for tolerance and that it can evolve in natural plant populations. Although tolerance is probably not a strict alternative to plant resistance, there could be inter- and intraspecific tradeoffs between these defensive strategies.

http://www.eeb.cornell.edu/agrawal/pdfs/1999/Tree-1999.pdf

The ecology and evolution of plant tolerance to herbivory.

▪ Abstract Plants respond to herbivore attack with a bewildering array of responses, broadly categorized as direct and indirect defenses, and tolerance. Plant-herbivore interactions are played out on spatial scales that include the cellular responses, well-studied in plant-pathogen interactions, as well as responses that function at whole-plant and community levels. The plant's wound response plays a central role but is frequently altered by insect-specific elicitors, giving plants the potential to optimize their defenses. In this review, we emphasize studies that advance the molecular understanding of elicited direct and indirect defenses and include verifications with insect bioassays. Large-scale transcriptional changes accompany insect-induced resistance, which is organized into specific temporal and spatial patterns and points to the existence of herbivore-specific trans-activating elements orchestrating the responses. Such organizational elements could help elucidate the molecular control over the d...

Plant responses to insect herbivory: The emerging molecular analysis

What determines the number and size of the seeds produced by a plant? How often should it reproduce them? How often should a plant produce them? Why and how are seeds dispersed, and what are the implications for the diversity and composition of vegetation? These are just some of the questions tackled in this wide-ranging review of the role of seeds in the ecology of plants. The authors bring together information on the ecological aspects of seed biology, starting with a consideration of reproductive strategies in seed plants and progressing through the life cycle, covering seed maturation, dispersal, storage in the soil, dormancy, germination, seedling establishment, and regeneration in the field. The text encompasses a wide range of concepts of general relevance to plant ecology, reflecting the central role that the study of seed ecology has played in elucidating many fundamental aspects of plant community function.

The ecology of seeds

Bees are the most important pollinator taxon; therefore, understanding the scale at which they forage has important ecological implications and conservation applications. The foraging ranges for most bee species are unknown. Foraging distance information is critical for understanding the scale at which bee populations respond to the landscape, assessing the role of bee pollinators in affecting plant population structure, planning conservation strategies for plants, and designing bee habitat refugia that maintain pollination function for wild and crop plants. We used data from 96 records of 62 bee species to determine whether body size predicts foraging distance. We regressed maximum and typical foraging distances on body size and found highly significant and explanatory nonlinear relationships. We used a second data set to: (1) compare observed reports of foraging distance to the distances predicted by our regression equations and (2) assess the biases inherent to the different techniques that have been used to assess foraging distance. The equations we present can be used to predict foraging distances for many bee species, based on a simple measurement of body size.

/pdf/bee-foraging-ranges-and-their-relationship-to-body-size-27ta66i106.pdf

Bee foraging ranges and their relationship to body size.

In order to estimate how much population extinction risk may be affected by local fragmentation, population viability analyses were performed in six populations of the endangered grassland herb Gentianella campestris in Sweden. The populations had been experimentally reintroduced to grasslands that were locally fragmented by juniper shrubs. The sites represented three sizes of grassland and two levels of grassland abundance in the landscape. Five years' demographic data were evaluated in a stochastic matrix population model, and studies of seed set, pollinator abundance, and inbreeding depression were performed in order to examine possible links between population viability and pollination. In all six sites, plants with reduced capacity of self-pollination (due to herkogamy) showed strongly reduced population viability in locally fragmented grassland habit, with pronounced extinction thresholds at certain levels of local fragmentation. Population viability was reduced because of inbreeding depression and reduced seed production in combination, both caused by pollinator deficit in locally fragmented grasslands. Plants with high selfing capacity had low population viability over the entire local fragmentation gradients. Selfing yielded high seed set in the absence of pollinators and was advantageous in fragmented parts of the grasslands. However, selfing had negative effects in nonfragmented parts of the grasslands, because it decreased the chances of cross-pollination and because selfed progeny had reduced fitness compared to outcrossed offspring. A comparison among the six sites indicated that the negative effects of local fragmentation were amplified by reduced size of the grassland sites and by reduced abundance of grassland habitat in the landscape. To my knowledge, this is the first quantitative estimate of increased extinction risk in fragmented plant populations.

Extinction thresholds and disrupted plant-pollinator interactions in fragmented plant populations

Land use more than 200 years ago explains current grassland plant diversity in a Swedish agricultural landscape

Swedish University of Agricultural Sciences, Department of Conservation Biology, Section of Conservation Botany, Box 7072, 750 07 Uppsala, Sweden; University of Oulu, Department of Biology, Linnanmaa, 90 570 Oulu, Finland, and University of Lund, Department for Theoretical Ecology, Ecology Building, 223 62 Lund, Sweden; University of Lund, Department for Theoretical Ecology, Ecology Building, 223 62 Lund, Sweden

https://www.jstor.org/stable/10.1086/286043

Evidence for an evolutionary history of overcompensation in the grassland biennial Gentianella campestris (Gentianaceae).

We present field evidence for the induction of overcompensation, or increased fruit and seed yield as a consequence of damage, in the grassland biennial field gentian, Gentianella campestris (Gentianaceae). We compared equally sized clipped and unclipped plants in two populations in central Sweden during three years, 1992-1994, and plants clipped at different occasions, from 20 June to 2 August. Clipping once, by removing half of the biomass, significantly increased fruit production without affecting the number of seeds per fruit or seed mass. The degree of compensation was sensitive to the timing of clipping. Damage induced overcompensation only during a restricted inductive time period (ITP) in July. Plants clipped before about 1 July or after about 22 July achieved no overcompensation. The early limit of ITP was presumably determined by the availability of resources that could be mobilized for regrowth after damage. The late limit, on the other hand, depended primarily on the differentiation of meristems close to flowering in early August. The effects of clipping varied between years, presumably due to drought in 1994. During 1992-1993, plants consistently overcompensated for clipping on 1-20 July, whereas in 1994 only early clipping from 1 to 12 July induced overcompensation. In 1994, plants clipped in late July compensated less well, due to delayed fruit maturation leading to a high proportion of immature fruits at the end of the season. Because of this between-year variation, we used geometric mean fitness to calculate the expected long-term effects of damage over generations. The analysis suggests that the long-term effects can vary from positive to negative, depending on the frequency of bad fruiting years. The time limits of ITP fit well the hypothesis that predictable damage in July may have selected for a capacity of overcompensation in the field gentian. Because the ultimate limits of ITP are set by the length of the vegetation period, we expect overcompensation in this species to be more common in regions with a longer growing season.

Induction of overcompensation in the field gentian, gentianella campestris

Summary

1
 Transition matrix models were used to evaluate the effects of environmental stochasticity and four different methods of grassland management on dynamics and viability of a population of the biennial Gentianella campestris (Gentianaceae) in species-rich grassland. Data were collected between 1990 and 1995.

2
 Continuous summer grazing, the prevailing management strategy in Scandinavian grasslands, resulted in high recruitment of new plants, mainly because litter accumulation was prevented and gaps were created by trampling. Trampling and repeated grazing, however, caused damage which reduced seed production. Lambda for the average matrix was c. 0.77, and a stochastic matrix model yielded an extinction probability for the total population of c. 0.08 within 50 years.

3
 Mowing in mid-July (used as a conservation tool) increased seed production, but litter accumulation following re-growth of the vegetation prevented establishment. Lambda and extinction risk were similar to continuous grazing.

4
 Mowing in October (another conservation tool) promoted recruitment because of low litter accumulation, but the seed output decreased because plant growth was impaired by tall vegetation. Lambda was 0.64, while the extinction probability was very high (c. 0.98 within 50 years).

5
 Mid-July mowing followed by autumn grazing (the historical management regime) yielded high values for both seed production and establishment of rosettes. Lambda was 0.94 and the probability of extinction within 50 years was below detection level.

6
 Log-linear analysis showed that the matrices differed significantly both between treatments and between years. The latter indicates environmental stochasticity, here caused by summer drought that increased the extinction risk. Lambda may be slightly underestimated because drought occurred in one out of five summers during the study period, which is high compared with the natural frequency.

7
 We conclude that traditional grassland management is more favourable for G. campestris than the methods that prevail in Scandinavia today. This indicates a serious conservation problem, because grazing has replaced traditional management in many of the remaining semi-natural grasslands throughout Europe.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2745.2001.00566.x

Tommy Lennartsson

Papers

Extinction thresholds and disrupted plant-pollinator interactions in fragmented plant populations

Land use more than 200 years ago explains current grassland plant diversity in a Swedish agricultural landscape

Evidence for an evolutionary history of overcompensation in the grassland biennial Gentianella campestris (Gentianaceae).

Induction of overcompensation in the field gentian, gentianella campestris

Demographic variation and population viability in Gentianella campestris: effects of grassland management and environmental stochasticity