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

Soil Chemical Analysis

Multiple regression analyses were performed on a worldwide 236—site data set compiled from studies that compared species composition, aboveground net primary production (ANPP), root biomass, and soil nutrients of grazed vs. protected, ungrazed sites. The objective was to quantitatively assess factors relating to differential sensitivities of ecosystems to grazing by large herbivores. A key question in this assessment was: Do empirically based, broad—scale relationships correspond to ecological theories of plant—animal interactions and conceptual frameworks for management of the world's grazing lands? Changes in species composition with grazing were primarily a function of ANPP and the evolutionary history of grazing of the site, with level of consumption third in importance. Changes in species composition increased with increasing productivity and with longer, more intense evolutionary histories of grazing. These three variables explained >50% of the variance in the species response of grasslands or grasslands—plus—shrublands to grazing, even though methods of measurement and grazing systems varied among studies. Years of protection from grazing was a significant variable only in the model for shrublands. Similar variables entered models of change in the dominant species with grazing. As with species composition, sensitivities of change in dominant species were greater to varying ecosystem—environmental variables than to varying grazing variables, from low to high values. Increase of the dominant species under grazing were predicted under some conditions, and decreases were more likely among bunch grasses than other life—forms and more likely among perennials than annuals. The response of shrublands was different from that of grasslands, both in terms of species composition and the dominant species. Our analyses support the perception of grazing as a factor in the conversion of grasslands to less desirable shrublands, but also suggest that we may be inadvertently grazing shrublands more intensively than grasslands. Percentage differences in ANPP between grazed and ungrazed sites decreased with increasingly long evolutionary histories of grazing and increased with increasing ANPP, levels of consumption, or years of treatment. Although most effects of grazing on ANPP were negative, some were not, and the statistical models predicted increases in ANPP with grazing under conditions of long evolutionary history, low consumption, few years of treatment, and low ANPP for grasslands—plus—shrublands. The data and the models support the controversial hypothesis that grazing can increase ANPP in some situations. Similar to species variables, percentage differences in ANPP between grazed and ungrazed treatments were more sensitive to varying ecosystem—environmental variables than to varying grazing variables. Within levels not considered to be abusive "overgrazing," the geographical location where grazing occurs may be more important than how many animals are grazed or how intensively an area is grazed. Counter to the commonly held view that grazing negatively impacts root systems, there was no relationship between difference in ANPP with grazing and difference in root mass; as many positive as negative differences occurred, even though most ANPP differences were negative. Further, there was a weak relationship between change in species composition and change in ANPP, and no relationship with root mass, soil organic matter, or soil nitrogen. All three belowground variables displayed both positive and negative values in response to grazing. Current management of much of the world's grazing lands based on species composition criteria may lead to erroneous conclusions concerning the long—term ability of a system to sustain productivity.

Quantitative effects of grazing on vegetation and soils over a global range of environments

Herbivory by domestic and wild ungulates is a major driver of global vegetation dynamics. However, grazing is not considered in dynamic global vegetation models, or more generally in studies of the effects of environmental change on ecosystems at regional to global scale. An obstacle to this is a lack of empirical tests of several hypotheses linking plant traits with grazing. We, therefore, set out to test whether some widely recognized trait responses to grazing are consistent at the global level. We conducted a meta-analysis of plant trait responses to grazing, based on 197 studies from all major regions of the world, and using six major conceptual models of trait response to grazing as a framework. Data were available for seven plant traits: life history, canopy height, habit, architecture, growth form (forb, graminoid, herbaceous legume, woody), palatability, and geographic origin. Covariates were precipitation and evolutionary history of herbivory. Overall, grazing favoured annual over perennial plants, short plants over tall plants, prostrate over erect plants, and stoloniferous and rosette architecture over tussock architecture. There was no consistent effect of grazing on growth form. Some response patterns were modified by particular combinations of precipitation and history of herbivory. Climatic and historical contexts are therefore essential for understanding plant trait responses to grazing. Our study identifies some key traits to be incorporated into plant functional classifications for the explicit consideration of grazing into global vegetation models used in global change research. Importantly, our results suggest that plant functional type classifications and response rules need to be specific to regions with different climate and herbivory history.

Plant trait responses to grazing – a global synthesis

There must have been plenty of them about, growing up quietly and inoffensively, with nobody taking any particular notice of them…. And so the one in our garden continued its growth peacefully, as did thousands like it in neglected spots all over the world…. It was some little time later that the first one picked up its roots and walked. John Wyndham, The Day of the Triffids

https://www.jstor.org/stable/10.1641/0006-3568(2001)051[0103:HAAPOI]2.0.CO;2

Horticulture as a Pathway of Invasive Plant Introductions in the United States

— Cryptogamic soil crusts of Betatakin Canyon in Navajo National Monument were investigated to understand the influence of such crusts on soil moisture relationships and potential sediment production. Crusts sampled were part of the pinyon-juniper community and were studied in paired units. The presence of crusts on soils significantly increased the depth of water penetration and decreased runoff. Soils showed reduced infiltration of water where lichen and algal crusts were present and enhanced infiltration rates where mosses were present. Crusts appear to cause surface sealing and therefore likely reduce surface evaporation rates as well. Cryptogamic crusts are nonvascular plant communities that grow on or immediately beneath the soil surface. Such communities are components of most desert ecosystems. They have been described in several ecosystems in western North America (Anderson and Rushforth 1976, Anderson et al. 1982a) as well as in the deserts of the Middle East (Evenari et al. 1971). Until recently scant attention had been given them and little was known concerning their role in native ecosystems. Studies of the past decade indicate that they exert a significant impact on reducing soil erosion (Evenari et al. 1971, Loope and Gifford 1972, Kleiner and Harper 1972, Kleiner and Harper 1977, Anderson et al. 1982a, Anderson et al. 1982b). Fletcher and Martin (1948) found that fungal and algal crusts increase the tensile strength of soil. The algae appear to be the most effective in binding the surface soil particles (Durrell and Shields 1961) because of the thick gelatinous sheaths that enclose the trichomes of several algal species (Anderson and Rushforth 1976). Such gelatinous sheaths add strength and aggregating qualities to the I or 2 mm of surface soil upon which they grow (Anantani and Marathe 1974). Research on the biology of cryptogamic crusts has also been done in several other areas. These studies include taxonomy (Ali and Sandhu 1972, Anderson and Rushforth 1976); nitrogen fixation (MacGregor and Johnson 1971, Reddy and Gibbons 1975); land reclamation (Singh 1950); soil fertility (Shields and Durrell 1964); reproduction, growth and habitat relations (Evenari et al. 1971, Anderson et al. 1982b); and moisture (Booth 1941, Loope and Gifford 1972). The objective of this study was to investigate the influence of cryptogamic crusts in the pinyon-juniper woodlands of northeastern Arizona on depth of water penetration, infiltration, runoff, and potential sediment production.

/pdf/influence-of-cryptogamic-crusts-on-moisture-relationships-of-b4dogxeypc.pdf

Influence of cryptogamic crusts on moisture relationships of soils in Navajo National Monument, Arizona

Identifying Phytoliths Produced by the Inflorescence Bracts of Three Species of Wheat (Triticum monococcumL.,T. dicocconSchrank., andT. aestivumL.) Using Computer-Assisted Image and Statistical Analyses

Eight general study sites were examined in the blackbrush (Coleogyne ramosissima) zone of southwestern Utah in order to assess the impact of burning. All sites had been burned. Age since burning varied from 1 to 37 years. Plots were placed in bumed areas with plots in adjacent unburned areas serving as controls. Sites were similar enough that definite trends were distinguishable despite between site variation. Recently burned areas were dominated by forbs, middle aged burns were dominated by grasses, and the oldest burns had reverted back to shrub dominance. Cryptogamic soils crusts were severely affected by burning and showed no signs of recovery after 19.5 years. Blackbrush was also severely affected and showed no signs of recovery after 37 years. Lack of recovery by blackbrush may be due to its paleoendemic nature. Future burning of stands of blackbrush in southwestern Utah is not recommended.

/pdf/the-effects-of-fire-on-the-blackbrush-coleogyne-ramosissima-2bqntfjbwa.pdf

The effects of fire on the blackbrush (Coleogyne ramosissima) community of southwestern Utah.

The effects of long-term grazing (40 years) on cryptogamic crusts of Navajo National Monument were investigated. Both vascular and nonvascular communities were heavily impacted with the cryptogamic community showing the greatest reduction in cover. Lichens and mosses were the most damaged, while the algae were much more tolerant. Individual cryptogamspeeies were affected in similar patterns with all identifuble species showing reduced cover. Vascuhr plant species were also affected with grassesshowing the greatest reduction under grazing pressure. Throughout desert systems of western North America there is scant ground cover and often extensive open areas between the plants. In such open areas, soils are exposed to powerful erosive impacts. When soils are unprotected, erosion can be extensive and soil losses can be great. Of primary importance in the protection of desert soils are communities of nonvascular cryptogamic plants that grow upon or immediately beneath the soil surface. When well established and undisturbed such plants form a crust which plays an important role in soil stabilization (Fletcher and Martin 1948; Kleiner and Harper 1972, 1977; Loope and Gifford 1972; Anderson et al. 1982a, 1982b). Algae are the primary components of these crusts but they are often accompanied by lichens and mosses (Anderson and Rushforth 1977, Kleiner and Harper 1972). Algae are the most effective in binding the soil particles (Anantani and Marathe 1974, Anderson and Rushforth 1976). Where cryptogam crusts are well developed the soil surface is almost always highly stable. Research has been done on several aspects of the biology of soil crusts and cryptogamic communities. Ecological relationships have been studied by Anderson et al. (1982a) and Anderson et al. (1982b). Species composition and taxonomic relationships of crusts were studied by Anderson and Rushforth (1976). The role of such crusts in nitrogen fixation was studied by Rychert and Skujins (1974) and their effects on infiltrationand sedimentation by Loope and Gifford (1972). However, much is yet to be learned about the role of these crusts in desert ecosystems. The Navajo National Monument boundary (fenceline) provided an excellent opportunity to evaluate the effects of grazing on the cryptogamic soil crusts of the pinyon-juniper zone in northeastern Arizona. The objective of this study was to evaluate the effects of long-term grazing (40 years) on the cryptogamic soil cover of the pinyon-juniper zone in northern Arizona (Navajo National Monument).

/pdf/effects-of-long-term-grazing-on-cryptogam-crust-cover-in-39ota8gi4j.pdf

Effects of long-term grazing on cryptogam crust cover in Navajo National Monument, Arizona.

Variation between phytoliths produced in the laminae, inflorescence bracts, and culms of einkorn (Triticum monococcum L.) were examined. Variation in the type of phytoliths produced and in the morp...

Jack D. Brotherson

Papers

Influence of cryptogamic crusts on moisture relationships of soils in Navajo National Monument, Arizona

Identifying Phytoliths Produced by the Inflorescence Bracts of Three Species of Wheat (Triticum monococcumL.,T. dicocconSchrank., andT. aestivumL.) Using Computer-Assisted Image and Statistical Analyses

The effects of fire on the blackbrush (Coleogyne ramosissima) community of southwestern Utah.

Effects of long-term grazing on cryptogam crust cover in Navajo National Monument, Arizona.

A typologic and morphometric study of variation in phytoliths from einkorn wheat (Triticum monococcum)