We conducted a greenhouse study of the effects of initial seed mass on seedling characteristics in a Panamanian population of Virola surinamensis, a canopy tree in which mean seed mass of different individuals ranges from 1.34 to 4.04g. The system is of particular interest because birds preferentially eat fruits of small-seeded plants, leaving seedlings of large-seeded individuals under conditions of potentially severe sibling competition (Howe and Vande Kerckhove 1980).Effects of differences of mean seed mass between trees are explored using an analysis of variance, while effects of seed-mass variation within crops are demonstrated with a regression analysis. A two-way analysis of variance decisively shows effects of parental source and light condition on seedling height, leaf length, and dry shoot mass (all P<0.0001). A posteriori tests show that differences in seedling characteristics reflect differences in initial seed mass, with especially strong differences apparent in shoot mass. Regression of seedling characteristics on initial seed mass shows that variation of seed size within a crop is sufficient to influence shoot mass at 15 weeks (P<0.0001).Effects of size differences of seeds that land adjacent to each other, either under the parent or in monkey droppings, are documented with growth of pairs of seedlings in pots. Differences in shoot height and mass at 15 weeks are evident when seeds of average size differ by only 0.2 g, and dramatic differences are evident when paired seeds differ by an average of 1.5 g. Seedlings grow more when isolated than when planted with conspecifics.These experimental results offer indirect support for the hypothesis that small-seeded Virola parents secure an advantage in reproduction through differential dispersal, while large-seeded plants produce more competitive seedlings under their own crowns - an advantage most likely to be of importance when frugivores are scarce.

No abstract

I conducted a study on survival and growth of nestling Yellow—headed Blackbirds (Xanthocephalus xanthocephalus). I examined the following hypotheses on the nature of variation in clutch size among the individuals of a breeding population: (1) clutch size variation is maintained by reversing selection favoring different clutch sizes in different years, (2) clutch size variation reflects a trade—off between offspring number and quality, and (3) the clutch size laid by an individual is determined by its ability to rear offspring under prevailing conditions of physiology or territory. I found no influence of clutch size on either survival or growth in a poor year in which 41% of those birds hatching ultimately starved. These results argue against the first hypothesis, rule out of the second, and favor the third. Individual nests of this species show a high level of hatching asynchrony, with over one—third of the nests hatching no more than one offspring per day, and few ever having more than two hatchlings in a single day. By causing older birds to get a head start in growth, hatching asynchrony promotes efficient brood reduction of younger nestlings under conditions of food stress. At the same time, hatching order has no effect on the growth of those birds fledging, indicating that those birds not eliminated suffer no impairment due to their position in the brood. The extreme dependence of survival on hatching position, coupled to processes producing adequate growth of all fledging birds, is an adaptive response to breeding under conditions where weather may suddenly charge adversely. Yellow—headed Blackbirds show an ecological trade—off between those breeding habitats having a high likelihood of nest predation and favorable feeding conditions, and those that are relatively safe from predation but poor for provisioning the young.

Buttresses of~owland tropical forest trees have long been thought to serve as structural supports. This morphometnc~l study of the buttresses and other characteristics of Quararibea asterolepzs demonstr~tes and descnbes the nature of the support role played by buttresses. Buttresses tend to grow on the side of the tree that faces the prevailing winds, thereby functioning as tension members that help prevent th_e ~ree from bei~g blown over. The buttresses become proportionately larger as th_e tree grows, prov1dmg the tree With g~eater support as its crown becomes exposed to the stronger WI~ds ?fthe upJ_Jer forest canopy. In particular, buttress height increases much faster than tree height. This di~proportiOnate mcrease r~duces by ::::: 15% the potential vulnerability of the trunk to snapping o.r tw1stmg under stress due to wmds. On the other hand, no specific relationship independent of tree Size can be demonstrated between the length of a buttress and the radius of the crown above or opposite that butt:ess. There is thus no evidence that buttresses counteract stresses due to crown asymmetries of a particular tree..

Geographic information adds a powerful component to environmental epidemiology studies but can compromise subject confidentiality. Although locations are often masked by perturbing spatial coordinates, existing masks do not ensure that the perturbation area contains a sufficient number of valid surrogates to prevent disclosure, nor are they designed to minimize perturbation while maintaining a specified level of privacy. I introduce a new approach to geoprivacy in which real property parcel data with information about land use are used to develop a pool of verified neighbors. GIS (geographic information system) processing optionally restricts the pool to residences with values of environmental variables similar to those of the subject parcel. A surrogate is then randomly selected from the k members of the pool closest to the subject with k chosen to achieve the desired spatial privacy protection. The method guarantees the specified level of privacy even where population density is uneven while minimizing spatial distortion and changes to the values of environmental variables assigned to subjects. The method is illustrated with an example that found it to be more effective than random perturbation-based methods in both protecting privacy and preserving spatial fidelity to the original locations.