The Ecology of Hydric Hammocks - USGS National Wetlands ...

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Consumption of fleshy fruits by residentand migrant birds has not beenexamined irl ityCir i~ iia~tltlt~~k, but it hasbeen studied in mesic hammock inFlorida (Skeate 1987). Most speciesof frugivorous birds are mutual isticseed-di spersers ; only three species(northern cardinal, summer tanager,and rose-breasted grosbeak, Pheucticus7udovicianus) are fruit "thieves" thatate the pulp and dropped the seed,undi spersed, be1 ow the parent plant.Consequently the support of this segmentof the dvifauna has re~ipro~dlimp1 icati ons for the reproduction andresilience of a subset of the plantcommunity. In mesic hammock this mutualism involves 22 species of birdsand 45 species of plants, dominated bymigrant species of birds and plantsthat fruit in fall or fall -to-winter.The greatest proportions of fruits areeaten by wintering American robins(57%) and cedar waxwings (20%); thegreatest diversity of fruits are eatenby wintering robins (18 species) andhermit thrushes (Catharus guttatus, 16species). The pace of seed-dispersalquickens in September and October, beginningwith arrival of four transientspecies of thrushes and continuingwith the arrival of wintering robins,waxwings, hermit thrushes, and ye1 1 owrumpedwarblers (Figure 39). By thepeak of seed-dispersal activity in December,28 species of bi rd-di spersedplants are in fruit, being consumed by10 winter and 4 year-round residentspecies of bird. Seed-di spersal activitydiminishes in March, and byApril -May only 3 species of bird-dispersedplants are in fruit, and thedisperser association diminishes to 4summer and 4 year-round residentspecies of bird. This forest has proportionatglyless summer fruiting (atotal of 9 species) and more winterfruiting (4 species in addition to the19 fall-winter fruiting species) thanin a forest in Illinois.Maintenance and elaboration of theassociation of bird and plant mutualist~is thought to be driven by afew pairs of strongly interactingbirds and plants (Skeate 1987). Theseare the veery (Catharus fuscescens)with Virginia creeper (Parthenocissus1BIRD-FRUIT DISPERSAL IN HAMMOCKSFigure 39. Phenology of bird diversity and abundanceand the number of species of plantsproducing fruits edible to birds in a mesic hammockin San Felasco State Preserve, AlachuaCounty, Florida (Skeate 1987).quinquefo7 ia) , Aral ia spinosa, andflowering dogwood (Cornus f 1 orida) ;robins with dogwood, red bay (Perseaborbonia), and cherry laurel (Prunuscaro7iniana) ; and waxwings withmistletoe (Phoradendron serotinum) .All these plants provide excellentfood because their fruits are unusuallyrich in lipids. Consumption of
these primary dietary items indirectlyc..,,I uvors seed dispersa: of other specie:that are less common or have less rewardingfruits, because the primaryfrugivores have varied diets. At thesame time, less abundant or effectivespecies of frugivorous birds, eachwith its own varied diet, are encouragedin the association by the predictablytimely resource of a varietyof fruits. Wide-ranging species ofprimary plants with high-1 ipid fruit(creeper, dogwood) supply rnigrati ngfrugivores with a high-qua1 i ty supplyof food continuously during migrationsouthward through the Atlantic flyway,and similar species with ranges restrictedto the southeastern UnitedStates offer resources to support thebird popul ati ons during winter.Another mutualism that may be importantin succession or invasion of hydrichammock is an association of treeswall ows and ye1 1 ow-rumped warblerswith wax-myrtl e and a microorgani sm(the soi 1 bacteri um Frankia) . Thisinteraction is important because ofthe aggressive pioneering of waxmyrtle,made possible by the nitrogenfixingof its actinomycete-nodul atedroots, its allelopathy to young competi tors, and its broadcast dispersalby large flocks of overwintering, omnivorousbirds (Schnoes and Humphrey1987).General i zed consumers (such as raccoonsand bears) and scatter-hoarders(such as blue jays and gray squirrels)also are prominent dispersers of seedsof plants of hydric hammock.Seedlings of cabbage palm and red bayhave been observed growing in bearscats (Maehr 1984). The diversity ofdrupes and herrips eaten bv bears andraccoons suggests the size of the assemblage of mutual i sts involved. A1 -though general ized consumers usuallykill nuts by eating them and hence donot benefit oak trees, acorns nonethelessare crucial to the interactiveroles of general i zed consumers by at -tracting them to the sites where drupesand berries also are eaten anddispersed. In contrast, jays andsquirrel s store nuts (especial 1 yacorns) individually in the soil for1 ater consumption. Nuts forgotten orleft because of death or departure ofthe consumer contribute to reproductionof the mature forest or successionafter disturbance or lumbering ofthe forest.The diversity of mast-producingspecies in southern forests produces acomposite phenol ogy yielding foodyear-round for generalized consumerscapable of eating both hard and softmast (Harris et a7. 1979). However,the continuity of this supply is incompletewithin specific types of forest.For example, little hard mast isproduced in hydric hammock in winter,and duration of the hiatus betweenconsumption of the last acorns andavailability of the first elm andmaple seeds varies according to thevolume of the year's acorn crop. Tobridge discontinuities in the seasonalfood supply, juxtaposition or interspersionof two or more types of forestis critically important to manymobile or large species of wild1 ifethat move tc find food. Documentedexamples are given in the discussionof individual species of mammals andbirds, Chapter 4.
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Copies of this publication may be o
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DISCLAIMERThe opinions and recommen
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CONVERSION TABLEMetric to U.S. Cust
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FIGURESNumber1AL...............Dist
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NumberTABLESPaqeClassifications of
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CHAPTER 1. INTRODUCTION"Hammock, ho
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whereas hydric hammock is a still-w
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CHAPTER 2. PHYSICAL SElTiNG2.3 CLIM
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Recent and PIe~sIoLene sands clay m
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ern vegetation associations formed-
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Table 3. Comparison of surface soil
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throughout the year in Florida, and
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Figure 13. Flooding and drydown of
Page 29 and 30: +southari:magnolla+-------cabbage p
Page 31 and 32: frequency may be once per year in f
Page 33 and 34: Table 4. Plants occurring in hydric
Page 35 and 36: Table 4. (Continued).Scientific nam
Page 37 and 38: of the subcanopy and shrub layers i
Page 39 and 40: sites were not chosen randomly;rath
Page 41 and 42: When present in a hydric hammock,ca
Page 43 and 44: hydric harriniock forests. These sp
Page 45 and 46: was the most frequent shrub in the
Page 47 and 48: Gulf Hammock is rep1 aced abruptly
Page 49 and 50: A sequence of changes in plantmat a
Page 51 and 52: I ~ U mapleswamp laurel oak 3:1100b
Page 53 and 54: The salt concentration of hydricham
Page 55 and 56: Cabbage palm is the most fire-toler
Page 57 and 58: frequent fires, a1 though timber ha
Page 59: Figure 38. Tree blowdowns due to hu
Page 62 and 63: locally collected litter lost 85% o
Page 64 and 65: Table 7. Occurrence of reptiles and
Page 66 and 67: Table 8. Occurrence of reptiles and
Page 68 and 69: 4.3 BIRDS4.3.1 Community StructureM
Page 70 and 71: Table 11. (Concluded).- ----Variabl
Page 72 and 73: and cerambyci d beet1 es) . Unl i k
Page 74 and 75: no specific habitat preference; it
Page 76 and 77: not take place in years of mast fai
Page 78 and 79: Graves 1977). These observations su
Page 82 and 83: CHAPTER 6. LINKAGES WITH OTHER ECOS
Page 84: R Amerlcan swallow-tailed kite b. t
Page 87: Conner, W.H., and J.W. Day, Jr. 197
Page 90 and 91: Duck foods in managed tidalimpoundm
Page 92 and 93: Puri, M,S., 3.W, Yon, and W.R.Ogles
Page 94 and 95: Wharton, C.H. 1977. The naturalenvi
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