Putting Density Back into the Habitat‐Quality Equation: Case Study of an Open‐Nesting Forest Bird

Abstract: Ecological traps and other cases of apparently maladaptive habitat selection cast doubt on the relevance of density as an indicator of habitat quality. Nevertheless, the prevalence of these phenomena remains poorly known, and density may still reflect habitat quality in most systems. We examined the relationship between density and two other parameters of habitat quality in an open‐nesting passerine species: the Ovenbird (Seiurus aurocapilla). We hypothesized that the average individual bird makes a good decision when selecting its breeding territory and that territory spacing reflects site productivity or predation risk. Therefore, we predicted that density would be positively correlated with productivity (number of young fledged per unit area). Because individual performance is sensitive to events partly determined by chance, such as nest predation, we further predicted density would be weakly correlated or uncorrelated with the proportion of territories fledging young. We collected data in 23 study sites (25 ha each), 16 of which were located in untreated mature northern hardwood forest and seven in stands partially harvested (treated) 1–7 years prior to the survey. Density explained most of the variability in productivity (R²= 0.73), and there was no apparent decoupling between density and productivity in treated plots. In contrast, there was no significant relationship between density and the proportion of territories fledging ≥1 young over the entire breeding season. These results suggest that density reflects habitat quality at the plot scale in this study system. To our knowledge this is one of the few studies testing the value of territory density as an indicator of habitat quality in an open‐nesting bird species on the basis of a relatively large number of sizeable study plots.     

‘Ecomálaga’: an ecosystem analysis of the Mediterranean coast around Málaga, Spain

In October 1992, the Oceanographic Centre of Málaga of the Spanish Oceanographical Institute (IEO) started a monitoring project,Ecomálaga, which collects physical, chemical, biological and sedimentological data from the Alborán Sea shelf. The project is coordinated with similar projects in the Atlantic and Mediterranean Centres of IEO. The ultimate objective is to, understand the long-term changes of the essential marine-environmental parameters. So far, nine quarterly surveys have been carried out—from October 1992 to December 1994. The following variables were registered:abiotic: location weather, water temperature, salinity, pH, dissolved oxygen, chlorophyll a, nitrate, nitrite, phosphate, silicate,biotic: zooplankton biomass and species composition, and ichthyoplankton. The granulometric composition and organic matter content of sediments are also included. Data are stored in a computerized data base named Ecomálaga Data Base, with contributions from geology, physics, plankton biology and marine chemistry. The data base not only contains separate files for each research topic, but also allows for interchange between these files, resulting in a synoptic data output. It offers the users an output in the form of synthetic records of each station sampled. The analysis of the data indicates seasonal influences and ainshore-offshore gradient, as well as an Atlantic influence on the stations located in the transect closest to the Strait of Gibraltar.     

Long‐Term Impacts of Poaching on Relatedness,Stress Physiology,and Reproductive Output of Adult Female African Elephants

Abstract: Widespread poaching prior to the 1989 ivory ban greatly altered the demographic structure of matrilineal African elephant (Loxodonta africana) family groups in many populations by decreasing the number of old, adult females. We assessed the long‐term impacts of poaching by investigating genetic, physiological, and reproductive correlates of a disturbed social structure resulting from heavy poaching of an African elephant population in Mikumi National Park, Tanzania, prior to 1989. We examined fecal glucocorticoid levels and reproductive output among 218 adult female elephants from 109 groups differing in size, age structure, and average genetic relatedness over 25 months from 2003 to 2005. The distribution in group size has changed little since 1989, but the number of families with tusked old matriarchs has increased by 14.2%. Females from groups that lacked an old matriarch, first‐order adult relatives, and strong social bonds had significantly higher fecal glucocorticoid values than those from groups with these features (all females R²= 0.31; females in multiadult groups R²= 0.46). Females that frequented isolated areas with historically high poaching risk had higher fecal glucocorticoid values than those in low poaching risk areas. Females with weak bonds and low group relatedness had significantly lower reproductive output (R²[U]=0.21). Females from disrupted groups, defined as having observed average group relatedness 1 SD below the expected mean for a simulated unpoached family, had significantly lower reproductive output than females from intact groups, despite many being in their reproductive prime. These results suggest that long‐term negative impacts from poaching of old, related matriarchs have persisted among adult female elephants 1.5 decades after the 1989 ivory ban was implemented.     

Economics of Grassland Conversion to Cropland in the Prairie Pothole Region

Abstract: Much of the remaining grassland, particularly in North America, is privately owned, and its conversion to cultivated cropland is largely driven by economics. An understanding of why landowners convert grassland to cropland could facilitate more effective design of grassland‐conservation programs. We built an empirical model of land‐use change in the Prairie Pothole Region (north‐central United States) to estimate the probability of grassland conversion to alternative agricultural land uses, including cultivated crops. Conversion was largely driven by landscape characteristics and the economic returns of alternative uses. Our estimate of the probability of grassland conversion to cultivated crops (1.33% on average from 1979 to 1997) was higher than past estimates (0.4%). Our model also predicted that grassland‐conversion probabilities will increase if agricultural commodity prices continue to follow the trends observed from 2001 to 2006 (0.93% probability of grassland conversion to cultivated crops in 2006 to 1.5% in 2011). Thus, nearly 121 million ha (30 million acres) of grassland could be converted by 2011. Conversion probabilities, however, are spatially heterogeneous (range 0.2% to 3%), depending on characteristics of a parcel (e.g., soil quality and economic returns). Grassland parcels with relatively high‐quality land for agricultural production are more likely to be converted to cultivated crops than lower‐quality parcels and are more responsive to changes in the economic returns on alternative agricultural land uses (i.e., conversion probability increases by a larger magnitude for high‐quality parcels when economics returns to alternative uses increase). Our results suggest that grassland conservation programs could be proactively targeted toward high‐risk parcels by anticipating changes in economic returns, such as could occur if a new biofuel processing plant were to be built in an area.     

Limitations of Gravity Models in Predicting the Spread of Eurasian Watermilfoil

Abstract: The effects of non‐native invasive species are costly and environmentally damaging, and resources to slow their spread and reduce their effects are scarce. Models that accurately predict where new invasions will occur could guide the efficient allocation of resources to slow colonization. We assessed the accuracy of a model that predicts the probability of colonization of lakes in Wisconsin by Eurasian watermilfoil (Myriophyllum spicatum). We based this predictive model on 9 years (1990–1999) of sequence data of milfoil colonization of lakes larger than 25 ha (n =1803). We used milfoil colonization sequence data from 2000 to 2006 to test whether the model accurately predicted the number of lakes that actually were colonized from among the 200 lakes identified as being most likely to be colonized. We found that a lake's predicted probability of colonization was not correlated with whether a lake actually was colonized. Given the low predictability of colonization of specific lakes, we compared the efficacy of preventing milfoil from leaving occupied sites, which does not require predicting colonization probability, with protecting vacant sites from being colonized, which does require predicting colonization probability. Preventing organisms from leaving colonized sites reduced the likelihood of spread more than protecting vacant sites. Although we focused on the spread of a single species in a particular region, our results show the shortcomings of gravity models in predicting the spread of numerous non‐native species to a variety of locations via a wide range of vectors.     

Evidence of Local Adaptation in the Demographic Response of American Ginseng to Interannual Temperature Variation

Abstract: Bioclimatic envelope models of species’ responses to climate change are used to predict how species will respond to increasing temperatures. These models are frequently based on the assumption that the northern and southern boundaries of a species’ range define its thermal niche. However, this assumption may be violated if populations are adapted to local temperature regimes and have evolved population‐specific thermal optima. Considering the prevalence of local adaptation, the assumption of a species‐wide thermal optimum may be violated for many species. We used spatially and temporally extensive demographic data for American ginseng (Panax quinquefolius L.) to examine range‐wide variation in response of population growth rate (λ) to climatic factors. Our results suggest adaptation to local temperature, but not precipitation. For each population, λ was maximized when annual temperatures were similar to site‐specific, long‐term mean temperatures. Populations from disparate climatic zones responded differently to temperature variation, and there was a linear relation between population‐level thermal optima and the 30‐year mean temperature at each site. For species that are locally adapted to temperature, bioclimatic envelope models may underestimate the extent to which increasing temperatures will decrease population growth rate. Because any directional change from long‐term mean temperatures will decrease population growth rates, all populations throughout a species’ range will be adversely affected by temperature increase, not just populations at southern and low‐elevation boundaries. Additionally, when a species’ local thermal niche is narrower than its range‐wide thermal niche, a smaller temperature increase than would be predicted by bioclimatic envelope approaches may be sufficient to decrease population growth.     

Reduced Density and Nest Survival of Ground‐Nesting Songbirds Relative to Earthworm Invasions in Northern Hardwood Forests

Abstract: European earthworms (Lumbricus spp.) are spreading into previously earthworm‐free forests in the United States and Canada and causing substantial changes, including homogenization of soil structure, removal of the litter layer, and reduction in arthropod abundance and species richness of understory plants. Whether these changes affect songbirds that nest and forage on the forest floor is unknown. In stands with and without earthworms in the Chequamegon‐Nicolet National Forest, Wisconsin (U.S.A.), we surveyed for, monitored nests of, and measured attributes of habitat of Ovenbirds (Seiurus aurocapillus) and Hermit Thrushes (Catharus guttatus), both ground‐dwelling songbirds, and we sampled earthworms at survey points and nests. Bird surveys indicated significantly lower densities of Ovenbirds and Hermit Thrushes in relation to Lumbricus invasions at survey point and stand extents (3.1 and 15–20 ha, respectively). Modeling of Ovenbird nest survival (i.e., the probability that nestlings successfully fledge) indicated that lower survival probabilities were associated with increased sedge cover and decreased litter depth, factors that are related to Lumbricus invasions, possibly due to reduced nest concealment or arthropod abundance. Our findings provide compelling evidence that earthworm invasions may be associated with local declines of forest songbird populations.     

Conservation Planning with Multiple Organizations and Objectives

Abstract: There has been a dramatic increase in the number of conservation organizations worldwide. It is now common for multiple organizations to operate in the same landscape in pursuit of different conservation goals. New objectives, such as maintenance of ecosystem services, will attract additional funding and new organizations to conservation. Systematic conservation planning helps in the design of spatially explicit management actions that optimally conserve multiple landscape features (e.g., species, ecosystems, or ecosystem services). But the methods used in its application implicitly assume that a single actor implements the optimal plan. We investigated how organizational behavior and conservation outcomes are affected by the presence of autonomous implementing organizations with different objectives. We used simulation models and game theory to explore how alternative behaviors (e.g., organizations acting independently or explicitly cooperating) affected an organization's ability to protect their feature of interest, and investigated how the distribution of features in the landscape influenced organizations’ attitudes toward cooperation. Features with highly correlated spatial distributions, although typically considered an opportunity for mutually beneficial conservation planning, can lead to organizational interactions that result in lower levels of protection. These detrimental outcomes can be avoided by organizations that cooperate when acquiring land. Nevertheless, for cooperative purchases to benefit both organizations’ objectives, each must forgo the protection of land parcels that they would consider to be of high conservation value. Transaction costs incurred during cooperation and the sources of conservation funding could facilitate or hinder cooperative behavior.     

Effects of Economic Downturns on Mortality of Wild African Elephants

Abstract: Declines in economic activity and associated changes in human livelihood strategies can increase threats of species overexploitation. This is exemplified by the effects of economic crises, which often drive intensification of subsistence poaching and greater reliance on natural resources. Whereas development theory links natural resource use to social‐economic conditions, few empirical studies of the effect of economic downturns on wild animal species have been conducted. I assessed the relations between African elephant (Loxodonta africana) mortality and human‐caused wounds in Samburu, Kenya and (1) livestock and maize prices (measures of local economic conditions), (2) change in national and regional gross domestic product (GDP) (measures of macroeconomic conditions), and (3) the normalized difference vegetation index (NDVI) (a correlate of primary productivity). In addition, I analyzed household survey data to determine the attitudes of local people toward protected areas and wild animals in the area. When cattle prices in the pastoralist study region were low, human‐caused wounds to and adult mortality of elephants increased. The NDVI was negatively correlated with juvenile mortality, but not correlated with adult mortality. Changes in Kenyan and East Asian (primary market for ivory) GDP did not explain significant variation in mortality. Increased human wounding of elephants and elephant mortality during periods of low livestock prices (local economic downturns) likely reflect an economically driven increase in ivory poaching. Local but not macroeconomic indices explained significant variation in mortality, likely due to the dominance of the subsistence economy in the study area and its political and economic isolation. My results suggest economic metrics can serve as effective indicators of changes in human use of and resulting effects on natural resources. Such information can help focus management approaches (e.g., antipoaching effort or proffering of alternative occupational opportunities) that address variation in local activities that threaten plant and animal populations.