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Forest birds in landscape mosaics: theory and empirical evidence Cristián F. Estades Theory of Island Biogeography (MacArthur & Wilson 1963, 1967) extinction rate colonization Importance of: Island size Isolation N* Number of species Metapopulations (Levins 1969, 1970 Gilpin & Hanski 1991) dp = mp(1-p) - ep dt pˆ = 1 - e/m Ideal Free Distribution Suitability (Fretwell and Lucas 1970) G P Number of competitors Density dependent habitat selection Source - sink dynamics (Pulliam 1988) Sources (R > M, E > I) subsidize Sinks (R<M, E < I) Birds in habitat islands - agricultural landscapes Birds in Illinois forest fragments (Blake & Karr 1984) Species richness 30 20 10 p < 0.001 1 10 100 500 Forest fragment area (ha) 1.0 Probability . . .. . . . .. . 40 Incidence function of Red-eyed Vireo (Robbins et al. 1989) 0.8 0.6 0.4 0.2 0.0 0.3 3.2 32 320 3200 Forest fragment area (ha) Bird species richness (spp/plot) Birds in forest fragments in Southern Chile 20 18 16 14 12 10 8 6 4 2 0 20 18 16 14 12 10 8 6 4 p = 0.001 2 0 0.1 1 10 100 Forest fragment area (ha) Matrix: agricultural fields (Willson et al. 1994) 1000 p = 0.07 0.1 1 10 100 Forest fragment area (ha) Matrix: pine plantations (Estades & Temple 1999) 1000 Extended foraging area d d d d d: maximum distance of foraging trip Mosaic approach (Wiens 1995) General theoretical framework (but is it really workable?) Landscape Mosaics are too Idiosyncratic Mosaic approach Habitat mosaic Quality Suitability Fitness etc... Resource mosaic Cover Nest sites Food 1. The effect of breeding-habitat patch size on bird population density Correlation between breeding-habitat patch size and bird population density A B 0 - C + A ? B B B ? C 0 Spatial covariance between food and nest sites + Individual based model: Goal: Explore the effect of relative distribution of food and nest sites on the relationship between breeding habitat patch size and bird density. 80 x 80 Breeding habitat Density Simulation model: results . . . ... Density Log (area) Log (area) Effect of flight distance General model Relationship between breeding-habitat patch size and bird population density + + Edge effects + Negative microclimate effects 0 + Competitor or predator release - 0 Spatial covariance between food and nest sites + Conclusions The effect of breeding-habitat patch size on bird population density depends on the relative location of food and nesting sites in the landscape. Management of the matrix may affect the suitability of fragmented landscapes for breeding birds The effect of additional foraging resources in the matrix on birds in fragmented habitat-patches depends on the species’ maximum flight distance and perceived foraging risk. 2. Spatial dynamics of bird communities in a forest landscape mosaic Problem The distributions of most forest bird species in the fragmented landscape of the Maule region are not adequately predicted by the size and/or isolation of forest patches (Estades and Temple, 1999). Hypotheses The distribution of bird species in a landscape can be modeled by looking at the distribution of food and nest sites. The distribution of birds in the landscape changes over time in accordance to the distribution of the limiting resources. During the breeding season the best predictor of the distribution of birds is the product of the local abundance of nest sites and food resources and during the non breeding season the best predictor is the abundance of food resources. Study area Maule Region, Chile Pine plantations 80% Native forests 10% Open areas 7% Others 3% 10,000 ha Dominant species: Nothofagus dombeyi Dominant species: Nothofagus glauca Dominant species: Pinus radiata Studied species Tufted Tit-tyrant Open-cup nester Understory Des Murs’Wiretail Open-cup nester Understory White-crested Elaenia Open-cup nester Understory and canopy Thorn-tailed Rayadito Cavity nester Fire-eyed Diucon Open-cup nester Understory and canopy White throated Treerunner Cavity nester Sampling 120 point count stations (variable radius point counts with correction for detectability) Field seasons: Winter (June) 1999 Spring (Oct-Nov) 1999 Summer (February) 2000 Winter (June) 2000 Spring (Oct-Nov) 2000 Summer (February) 2001 Model Breeding season Non-breeding Bird abundance = f(Nest sites * Food abundance) Bird abundance = f(Food abundance) Generalized linear model, negative binomial distribution Nest sites Food abundance . . . .. . . . . .. . ..... . . .. . . . 0 50 100 200m Diet Analysis of droppings Food abundance Foliage shaking Food abundance Aristotelia chilensis Fruit sampling Nest sites Abundance of cavities Density of understory Effect of nest site abundance and arthropod biomass on the abundance of cavity nesters Species and Season Thorn-tailed Rayadito Winter 1999 Spring 1999 Summer 2000 Winter 2000 Spring 2000 Summer 2001 White-throated Treerunner Winter 1999 Spring 1999 Summer 2000 Winter 2000 Spring 2000 Summer 2001 Cavities 0-50 m 0-100m 0-200m Arthropods 0-50 m 0-100m 0-200m Cavities * Arthropods 0-50 m 0-100m 0-200m + . +++ +++ +++ +++ ++ +++ +++ +++ +++ +++ . +++ +++ +++ +++ +++ ++ + + + + + . + + +++ . +++ ++ +++ +++ +++ +++ ++ + . : p<0.1, +: p<0.05, ++: p<0.01, +++: p<0.001. Bold: lowest AIC. +++ +++ +++ +++ +++ ++ +++ +++ ++ +++ +++ . +++ +++ +++ +++ +++ +++ ++ + + + . +++ + +++ ++ +++ +++ Effect of nest site abundance and arthropod biomass on the abundance of open-cup nesters Species and Season Tufted Tit-tyrant Winter 1999 Spring 1999 Summer 2000 Winter 2000 Spring 2000 Summer 2001 Understory 0-50 m 0-100m 0-200m + Des Murs' Wiretail Winter 1999 Spring 1999 . Summer 2000 . Winter 2000 Spring 2000 +++ Summer 2001 ++ + +++ + +++ Arthropods 0-50 m 0-100m 0-200m Understory * Arthropods 0-50 m 0-100m 0-200m ++ + . . + +++ . : p<0.1, +: p<0.05, ++: p<0.01, +++: p<0.001. Bold: lowest AIC. +++ +++ + +++ Effect of food abundance on the abundance of White-crested Elaenias Season Spring 1999 Summer 2000 Spring 2000 Summer 2001 Arthropods 0-50 m 0-100m 0-200m + + Fruits 0-50 m 0-100m 0-200m Fruits * Arthropods 0-50 m 0-100m 0-200m + + + . : p<0.1, +: p<0.05, ++: p<0.01, +++: p<0.001. Bold: lowest AIC. Conclusions Most studied birds changed their distributions in the landscape between seasons and many of these changes matched the changes in the distribution of key resources. Although factors such as competition, predation and parasitism may influence the distribution of birds in a landscape mosaic, the “resource mosaic”model represents a parsimonious approach to understanding the distribution of birds in a patchy landscape where the matrix surrounding patches of preferred habitat is not completely useless 3. Nest success of the Thorn-tailed Rayadito in a forest landscape mosaic Problem Thorn-tailed Rayaditos in the Maule region have higher densities in smaller forest fragments because these birds can forage in the surrounding pine plantations (Estades and Temple, 1999). But is the breeding success of birds that include pine plantations in their home ranges equal to the breeding success of birds that forage entirely in native forest? Hypothesis The breeding success of Thorn-tailed Rayaditos is positively associated with the amount of native vegetation around the nest because of the effect of reduced food concentration and a potentially higher level of predation in the artificial forests Upland forest native vegetation: 100% Riparian forest Pine plantations 25.5% 0% 50m 1.34 1.13 1.0 relative arthropod ab. Nest success of Thorn-tailed Rayaditos Most failures were due to predation No evidence of an effect of food density Thylamis elegans House Wren Rodent Nest predators Thylamis elegans Phylodrias chammisonis Predators of fledglings and adults Accipiter chilensis Glaucidium nanum Competitors Picoides lignarius Troglodytes aedon Liolaemus tenuis Pygarrichas albogularis Conclusions Concentration of food resources did not limit breeding performance of Thorn-tailed Rayaditos Small riparian forest fragments surrounded by pine plantations not only harbor higher rayadito densities than large upland forest patches (Estades and Temple, 1999), but they also provide a safer place to breed for this species. Differences in breeding success between habitat types were probably due to differences in concentration of predators and competitors and average nest height. Ongoing work Nest success and nesting density of open-cup nesters in different parts of the landscape Movements of individual birds in the landscape Acknowledgements •Fondecyt (Chile) grants 1990786 and 7990027 •Zoological Society of Milwaukee County •Association of Field Ornithologists •Dept. Wildlife Ecology. University of Wisconsin - Madison •School of Forest Sciences. Universidad de Chile (Santiago) •Committee: Stanley Temple, Nancy Mathews, Christine Ribic, Tony Ives, Tim Moermond •All the field assistants •Friends here and there •Paula and Josefa