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 influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km(2) yr(-1) since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr(-1) before 1940 to 7% yr(-1) since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.

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Accelerating loss of seagrasses across the globe threatens coastal ecosystems

Seagrasses, marine flowering plants, have a long evolutionary history but are now challenged with rapid environmental changes as a result of coastal human population pressures. Seagrasses provide key ecological services, including organic carbon production and export, nutrient cycling, sediment stabilization, enhanced biodiversity, and trophic transfers to adjacent habitats in tropical and temperate regions. They also serve as “coastal canaries,” global biological sentinels of increasing anthropogenic influences in coastal ecosystems, with large-scale losses reported worldwide. Multiple stressors, including sediment and nutrient runoff, physical disturbance, invasive species, disease, commercial fishing practices, aquaculture, overgrazing, algal blooms, and global warming, cause seagrass declines at scales of square meters to hundreds of square kilometers. Reported seagrass losses have led to increased awareness of the need for seagrass protection, monitoring, management, and restoration. However, seagrass science, which has rapidly grown, is disconnected from public awareness of seagrasses, which has lagged behind awareness of other coastal ecosystems. There is a critical need for a targeted global conservation effort that includes a reduction of watershed nutrient and sediment inputs to seagrass habitats and a targeted educational program informing regulators and the public of the value of seagrass meadows.

https://www.jstor.org/stable/10.1641/0006-3568(2006)56%5B987:AGCFSE%5D2.0.CO;2

A Global Crisis for Seagrass Ecosystems

Recent research has highlighted the valuable role that coastal and marine ecosystems play in sequestering carbon dioxide (CO(2)). The carbon (C) sequestered in vegetated coastal ecosystems, specifically mangrove forests, seagrass beds, and salt marshes, has been termed blue carbon. Although their global area is one to two orders of magnitude smaller than that of terrestrial forests, the contribution of vegetated coastal habitats per unit area to long-term C sequestration is much greater, in part because of their efficiency in trapping suspended matter and associated organic C during tidal inundation. Despite the value of mangrove forests, seagrass beds, and salt marshes in sequestering C, and the other goods and services they provide, these systems are being lost at critical rates and action is urgently needed to prevent further degradation and loss. Recognition of the C sequestration value of vegetated coastal ecosystems provides a strong argument for their protection and restoration; however, it is necessary to improve scientific understanding of the underlying mechanisms that control C sequestration in these ecosystems. Here, we identify key areas of uncertainty and specific actions needed to address them.

https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1890/110004

A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2

The literature, and previously unpublished data from the authors’ laboratories, shows that the δ13C of organic matter in marine macroalgae and seagrasses collected from the natural environment ranges from –3 to –35‰. While some marine macroalgae have δ13C values ranging over more than 10‰ within the thallus of an individual (some brown macroalgae), in other cases the range within a species collected over a very wide geographical range is only 5‰ (e.g. the red alga Plocamium cartilagineum which has values between –30 and –35‰). The organisms with very negative δ13C (lower than –30‰) are mainly subtidal red algae, with some intertidal red algae and a few green algae; those with very positive δ13C values (higher than –10‰) are mainly green macroalgae and seagrasses, with some red and brown macroalgae. The δ13C value correlates primarily with taxonomy and secondarily with ecology. None of the organisms with δ13C values lower than –30‰ have pyrenoids. Previous work showed a good correlation between δ13C values lower than –30‰ and the lack of CO2 concentrating mechanisms for several species of marine red algae. The extent to which the low δ13C values are confined to organisms with diffusive CO2 entry is discussed. Diffusive CO2 entry could also occur in organisms with higher δ13C values if diffusive conductance was relatively low. The photosynthesis of organisms with δ13C values more positive than –10‰ (i.e. more positive than the δ13C of CO2 in seawater) must involve HCO3- use.

Mechanistic interpretation of carbon isotope discrimination by marine macroalgae and seagrasses.

Seagrass degradation in Australian coastal waters

Coral death from sewage and phosphate pollution at Aqaba, Red Sea

Effect of boat moorings on seagrass beds near Perth, Western Australia

Research in the last decade has firmly established the importance of seagrass meadows to shallow coastal and estuarine ecosystems (Kemp, 1983 and references cited therein). Early studies (Westlake, 1963; McRoy and McMillan, 1977; Zieman and Wetzel, 1980) suggested that some seagrasses had primary productivities comparable with those of terrestrial crops, though more recent estimates (Larkum and West, 1983) set a more realistic upper limit while still acknowledging that seagrasses are amongst the most productive of submerged aquatic ecosystems. A number of authors (Wood et al., 1969; Thayer et al., 1975; den Hartog, 1977 ;Kemp, 1983) have outlined ways in which seagrass meadows function to maintain the productivity of coastal waters and estuaries and stabilize sediments, but the cornerstone of all these functions is the high productivity of the seagrasses themselves.

The high productivity of seagrasses implies a high nutrient demand, and some seagrass meadows may be nutrient limited, principally by the macronutrients nitrogen or phosphorus (Orth, 1977; Bulthuis and Woelkerling, 1981; Harlin and Thorne-Miller, 1981; Short et al., 1985). Seagrasses can tap both sediment and water column nutrients (McRoy and McMillan, 1977; lizumi and Hattori, 1982; Thursby and Harlin, 1982; Brix and Lyngby, 1985), and efficient uptake and utilization of essential nutrients, dynamic cycling and/or well developed nitrogen fixation must be important attributes of seagrass meadows (see Chapter 15).

The following account reviews Australian research on the primary production of seagrasses and nutrient limitation. Elsewhere, the majority of such research has involved the two species Thalassia testudinum and Zostera marina, neither of which occur in Australian waters. The results reviewed here therefore broaden the data base, to allow more meaningful generalizations and predictions about seagrass productivity in different ecosystems. The term 'primary production' is defined as in Larkum (1981) and is used where actual measurements on specific seagrasses are referred to. The term 'primary productivity' is used in the more general context, as when comparing different genera of seagrasses.

Diana Walker

Papers

Mechanistic interpretation of carbon isotope discrimination by marine macroalgae and seagrasses.

Seagrass degradation in Australian coastal waters

Coral death from sewage and phosphate pollution at Aqaba, Red Sea

Effect of boat moorings on seagrass beds near Perth, Western Australia

Productivity and nutrient limitation