The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration.

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We tested whether the herpetofaunal response to clearcutting followed by site preparation was similar to high-intensity wildfire followed by salvage logging in sandpine scrub. Herpetofaunal communities umre compared in three replicated 5-to 7-year post-disturbance treatments and mature sand-pine fores~ The three disturbance treatments were (1) high-intensity wildfir~ salvage-logging and natural regeneration; (2) clearcutting~ roller-choppin~ and broadcast-seeding; and (3) clearcutting and hracke-seeding. Animals were trapped over a 14.month period using pitfall traps with drift fences Microhabitat features were measured along line transec~ Because amphibian (frog) occurrence appeared to be unaffected by treatment this paper focuses only on reptile communitiex Six species of lizards and one snake species were numerically dominant Reptile species richnes~ diversity, and evenness did not differ among treat-Efecto de los incendios naturales de alta intensidad y de los tratamientos de silvicultura sobre las comunidades de reptiles en un brozal de ambiente arenoso Resumen: Se analiz6 si ia respuesta de ia herpetofauna a la taia seguida de ia preparaci6n del los sitio, fue similar a la respuesta a incendios naturales de alta intensidad seguidos por u~ta taia de rescat¢ en un brozal de pinos de ambiente arenoso. Se compararon ias comunidades de herpetofauna en 3 tratamientos (con r~plicas), luego de 5 a 7 a~os de finalizada ia pertubaciOn en bosques maduros de pinos de ambientes arenoso~ Los tres tratamientos de perturbaci6n fueron (1) incendio natural de alta intenstdatL tala de rescare y regeneraci6n natura~ (2) tala~ "roller-chopping" y "broadcast.seeding" y (3) taia y "'bracke-seeding" Los animales fueron atrapados a lo largo de un periodo mayor a 14 mese~ utilizando trampas disimulados. Las cazracteristicas de micyohdbttat fueron medidas a 1o largo de transecto, lineale~ Dado que la ocurrencia de anfthios (ranas) pareci6 no estar afectada por el tratumiento, este tra-1047 Conservation Biology, Pages 1047-1057 Volume 8, No. 4, December 1994 1048 He~etof~tma in S~d-Hne Scrub Gteenberg et ~d. ments or mature forest Species composition differed markedly, however, between mature forest and disturbance treat-ment& Typical open scrub species such us Cnemidophorus sexlineatus, Sceloporus woodi, and Eumeces egregius, were dominant in high-intensity burn, roller-chopped, and bracke-seeded stands but scarce in mature foresg and they were positively correlated with bare sand and other micro. habitat features typical of open scrub Conversely, Eumeces inexpectatus was most abundant in mature forest and was correlated with ground litter and other features typical of mature forest With respect to the species sampled, especially the lizards (including endemic species) of open scrub, clearcutting appeared to mimic high-intensity wildfire followed by salvage-logging by creating microhabitat features such as bare sand In a mirror image of the usual concep~ forest maturation historically served as the fragmenting agent of an extensive ...

Indirect climate effects on tree fecundity that come through variation in size and growth (climate-condition interactions) are not currently part of models used to predict future forests. Trends in species abundances predicted from meta-analyses and species distribution models will be misleading if they depend on the conditions of individuals. Here we find from a synthesis of tree species in North America that climate-condition interactions dominate responses through two pathways, i) effects of growth that depend on climate, and ii) effects of climate that depend on tree size. Because tree fecundity first increases and then declines with size, climate change that stimulates growth promotes a shift of small trees to more fecund sizes, but the opposite can be true for large sizes. Change the depresses growth also affects fecundity. We find a biogeographic divide, with these interactions reducing fecundity in the West and increasing it in the East. Continental-scale responses of these forests are thus driven largely by indirect effects, recommending management for climate change that considers multiple demographic rates.

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