摘要:

This study examines the species richness of bees and flower visiting wasps in seasonal neotropical habitats in Costa Rica. A total of 9231 individuals were netted at flowers. These represented 192 species of bees and 138 species of wasps. Over 50% of the bee individuals were eusocial Apidae, but there were only 12% of the bee species. There was less dominance among the wasp families. Most of the species in both groups were uncommon: 50% of the bee species were represented by fewer than 8 individuals, and over 50% of the wasp species had only 1 or 2 individuals. Previous comparisons of the species richness of bees in tropical and temperature areas have been complicated by different sample sizes and a lack of distinguishing within— and between—habitat diversity components. Here, comparisons are made of within—habitat species richness for structurally similar habitats. The within—habitat species richness of bees was higher in tropical forests than in the temperate forests previously described. The tropical grassland had lower bee species richness, and it is postulated that the coevolutionary history of a habitat is an important component of bee diversity. The higher species richness of tropical forests was correlated with the abundance and diversity of animal—pollinated plants. Tropical bees were not more temporally specialized despite the longer flowering seasons, so diversity and temporal specialization were not correlated. The average flight season of tropical species was 3 times longer than that reported for bees in most temperate areas, and the turnover in species was also similar. Seasonality was correlated with the degree of species' sociality: eusocial bees were essentially aseasonal. Most seasonal bee species were encountered in the dry season. Flower visiting wasps were much more diverse in the tropical habitats than reported for temperate habitats, and they overlap with bees in resource use. Many other taxa also fed at flowers, and such diversity among competitors may be a factor in limiting bee diversity in the tropics.

ISSN:0012-9658    

DOI:10.2307/1936480

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Data from dimension analysis of forest biomass and production are combined with analyses of plant tissues, soil, and precipitation to describe nutrient cycling in a cool—temperate deciduous forest on a podzol. Mean concentrations of nutrient elements measured (N, P, S, Ca, K, Mg, Mn, Na, Fe, Zn, Cu) in tissues are relatively low, and nutrient stocks in vegetation are low compared with other forests because of the low concentrations and the relative youth of the forest (cut in 1909—17). The largest fractions of nutrients in aboveground net primary production (NPP) go into leaves–58—78% of all nutrients except Na (45%)–although leaves are only 40% of aboveground NPP. Net community (woody) growth included °30% of aboveground NPP, but smaller fractions of nutrients (7% of N and K to 21% of Ca and 28% of Na). Nitrogen, P, and some other elements are retracted from dying leaves; but concentrations of Ca, Mn, and Na increase from living to dead leaves, branches, and stem wood. Return to the soil from aboveground is primarily by leaching for K and Na but by litterfall for other elements. "Throughflow" is defined as nutrient uptake needed beyond that in NPP to provide for both leaching and increase in dead tissues before they fall. For Na, throughflow exceeds uptake into NPP; but negative throughflows for N and P reflect conservation of these elements. Belowground plant nutrient stocks are 0.25 to 0.5x and belowground uptake rates into NPP are 0.1 to 0.2x aboveground values for most elements, but belowground values are higher for N, P, Na, and Fe. Significant amounts of some elements, especially S, Ca, K, and Na, are exuded from roots as part of the total, above— and belowground throughflow. Behaviors of nutrient elements can be characterized by ratios expressing concentration into leaves vs. woody tissues and relative leachability and throughflow vs. conservation. Relative turnover rates compare litterfall plus leaching with aboveground stocks or with nutrient contents of NPP. Turnover rates increase in the sequence: N and P; Ca; Mg, K, Fe, and Mn; S; and Na. Means and coefficients of variation of foliage nutrient concentrations express some differences between ecosystems. Comparing different ecosystems, coefficients of variation are low for N and P, intermediate for Ca, K, Mg, and Al, and high for Si, Mn, Fe, Cl, and Na. Differences in these and other expressions of element behavior can be interpreted on the basis of function in plants.

ISSN:0012-9658    

DOI:10.2307/1936481

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Populations of the multivoltine planthopper, Prokelisia marginata (Delphacidae), contain two wing—forms, flightless short—winged brachypters and macropters with fully developed wings capable of flight. P. marginata feeds selectively on the grass, Spartina alterniflora, which dominates the vegetation of Atlantic and Gulf Coast tidal salt marshes. We demonstrate that along most of the Atlantic seaboard S. alterniflora occurs as a harlequin environment composed of stable patches that provide life history requisites year—round and unstable ones that disappear altogether during winter. The proportion of macropters in planthopper population is significantly correlated with the proportion of unstable patches in the local environment. A dimorphism is maintained along most of the Atlantic Coast because brachypters remain and effectively exploit stable patches and macropters colonize and subsequently escape unstable habitats. Along the Gulf Coast S. alterniflora occurs as one rather stable habitat, and here planthopper populations are composed mostly of brachypters. The percentage of macropters in populations is positively correlated with levels of crowding incurred during the nymphal stage, suggesting that wing—form is determined by a developmental switching mechanism triggered by various environmental cues that predict habitat deterioration. The relationship between crowding and macroptery is linear at Atlantic and Gulf Coast localities, but greater proportions of macropters are produced on Atlantic marshes under similarly crowded conditions. As a mechanism to explain differences in the wing—morph composition of populations, we propose that selection has altered the threshold at which a developmental switch responds to environmental cues such as crowding.

ISSN:0012-9658    

DOI:10.2307/1936482

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936483

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936484

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936485

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936486

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936487

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936489

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1936490

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY