Quantifying the relative importance of direct and indirect effects influencing bird nestling growth

There is increasing evidence of indirect effects of hunting on populations. In species with sexually selected infanticide (SSI), hunting may decrease juvenile survival by increasing male turnover. We aimed to evaluate the relative importance of direct and indirect effects of hunting via SSI on the population dynamics of the Scandinavian brown bear ( Ursus arctos ). We performed prospective and retrospective demographic perturbation analyses for periods with low and high hunting pressures. All demographic rates, except yearling survival, were lower under high hunting pressure, which led to a decline in population growth under high hunting pressure ( λ = 0.975; 95% CI = 0.914–1.011). Hunting had negative indirect effects on the population through an increase in SSI, which lowered cub survival and possibly also fecundity rates. Our study suggests that SSI could explain 13.6% of the variation in population growth. Hunting also affected the relative importance of survival and fecundity of adult females for population growth, with fecundity being more important under low hunting pressure and survival more important under high hunting pressure. Our study sheds light on the importance of direct and indirect effects of hunting on population dynamics, and supports the contention that hunting can have indirect negative effects on populations through SSI.

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Relative influence of direct and indirect environmental effects on sestonic chlorophyll-a concentration in Cerrado streams

Acta Limnologica Brasiliensia ◽

10.1590/s2179-975x1815 ◽

2015 ◽

Vol 27 (3) ◽

pp. 301-310 ◽

Cited By ~ 5

Author(s):

Pedro Paulino Borges ◽

Fabrício Barreto Teresa ◽

Patrick Thomaz de Aquino Martins ◽

João Carlos Nabout

Keyword(s):

Chlorophyll A ◽

Primary Productivity ◽

Indirect Effects ◽

Important Variable ◽

Native Vegetation ◽

Aquatic Environments ◽

Relative Importance ◽

Direct And Indirect Effects ◽

Chlorophyll A Concentration ◽

Land Use And Cover

Abstract Aim: Chlorophyll-a may be directly influenced by local variables and/or indirectly by land use and cover, once landscape modifications change limnological variables, which in turn affect the primary productivity of aquatic environments, e.g., streams. Therefore, the objective of this study was to determine the relative importance of the local and landscape environmental components and assess the direct and indirect effects of these variables on sestonic chlorophyll-a concentration in 30 Cerrado streams (Santa Teresa River basin). Results All aquatic environments were oligotrophic during the study period. Only the local variables were important to explain chlorophyll-a variation (R2 = 0.27; P = 0.04). In addition, the path analysis showed that all variables used in the analysis influenced chlorophyll-a concentration more directly than indirectly. Conductivity was the most important variable to directly influence chlorophyll-a, followed by turbidity. Conclusion The large amount of remnant native vegetation in the basin indicates that the region studied is well preserved, which may explain the greater importance of local variables and the low effect of the landscape in explaining chlorophyll-a variation.

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