Sharon T. Pochron

The rules of disengagement: takeovers, infanticide, and dispersal in a rainforest lemur, Propithecus edwardsi

Summary Dispersal is a critical issue for understanding various aspects of animal biology and for conserving endangered species. We investigated the conditions that determine dispersal in four groups of sifakas inhabiting Ranomafana National Park, Madagascar. Following this population for 22 years, we collected and analyzed data on birth, relatedness, immigration, dispersal and death of 77 sifakas. We predicted that dispersal would function to prevent inbreeding and occur seasonally to aid establishment in a group before the breeding season. We further predicted that immigrants would evict same-sex residents and immigrant males would commit infanticide to shorten interbirth intervals. Although most dispersal theories predict male-biased dispersal in mammals, both male and female sifakas dispersed at equal rates from their natal and breeding groups. Behaviourally and genetically, there was no evidence for inbreeding within this population; individuals never produced offspring with close relatives. Dispersal matched the strong seasonal pattern of reproduction. Immigration events were always associated with the disappearance of the group infant(s). As a result of infanticide by male immigrants, mothers came into estrus sooner; infanticide by female immigrants caused mothers to disperse from their groups. This study reveals a clear pattern of dispersal that is condition, not sex, dependent.

Can Concurrent Speed and Directness of Travel Indicate Purposeful Encounter in the Yellow Baboons (Papio hamadryas cynocephalus) of Ruaha National Park, Tanzania?

I used components of baboon foraging behavior (concurrent fast and direct travel) to categorize core dry-season foods as purposefully or randomly encountered. I then compared the categorized foods to published, a priori predictions for core dry-season foods. Using focal-animal techniques on 6 males from two baboon troops, I collected precise locational data with a differentially corrected Global Positioning System (GPS) over 6 mo. The data analysis yielded the speed and directness of baboon travel between a food-handling event and a prior location. To distinguish purposefully encountered foods from randomly encountered foods, I calculated the average speed and the average observed deviation from straight-line travel exhibited to each resource type. A linear regression describes the relationship between these variables for each resource type. Baboons demonstrate both relatively high speeds and direct travel towards 3 food types: Combretum obovatum, impala, and baobab trees. Baboons were hypothesized a priori to encounter these resources purposefully. Baboons were also hypothesized a priori to encounter corms and perhaps Commiphora paniculatum purposefully, however, they travel neither quickly nor directly to these resources. I interpret this finding in terms of the costs accrued by traveling quickly and directly to fall-back resources. I discuss the ability of concurrent speed and directness to distinguish purposefully encountered foods from randomly encountered foods.

Temporal and geographic trends in mercury concentrations in muscle tissue in five species of hudson river, USA, fish

We analyzed a New York (USA) state database of mercury concentrations in muscle tissue for five species of fish (striped bass, yellow perch, largemouth bass, smallmouth bass, and carp) over a range of locations in the Hudson River (USA) between 1970 and 2004. We used regression models to discern temporal and geographic change in the fish while controlling for a positive correlation between mercury concentration and body mass. Mercury concentrations significantly increased in fish from New York Harbor waters to the mid-Hudson River. Striped bass and yellow perch showed a shallower increase in mercury concentration with river mile than did carp, largemouth bass, and smallmouth bass. Mercury concentrations declined over the 34-year period. These results imply that a geographically restricted source of mercury may be spread throughout the watershed by toxin-laden dispersing species. The increase of mercury toward the north may relate to a point source in the mid-Hudson River, or it may indicate mercury released from the Adirondack watershed. The decline of mercury over three decades corresponds to a reduction of various inputs in the region. The temporal and geographic pattern of mercury in sediments corresponds to the geographic trend of mercury in fish.

Does relative economic value of food elicit purposeful encounter in the yellow baboons (Papio hamadryas cynocephalus) of Ruaha National Park, Tanzania?

In the dry season, baboons traveled purposefully to spatially predictable foods that provided a relatively large number of grams per minute of preparation (e.g., economical foods), but not to predictable foods that merely accounted for a large proportion of feeding time (Pochron in Int J Primatol 22:773-785, 2001). In this paper, I examined the generality of those findings across seasons and applied the same methods to baboons eating a lush-season diet. I hypothesized that baboons should travel quickly and directly (i.e., purposefully) only to economical foods. The change in diet brought about by season provided an important comparison. In the lush season, none of the spatially predictable foods provided a relatively large number of grams per minute of preparation, so baboons were predicted to travel purposefully to no lush-season food. In short, baboons who traveled quickly and directly to some foods in the dry season were expected to use indirect and/or slow travel for all lush-season foods. The hypothesis was supported—baboons traveled quickly and directly to no lush-season food. Detailed comparisons between the dry- and lush-season characteristics of baobab fruit show that the food’s economic value relative to other foods predicts concurrent fast and direct travel, or the lack thereof, in both seasons.

The core dry-season diet of yellow baboons (Papio hamadryas cynocephalus)in Ruaha National Park, Tanzania.

Core dry-season foods consumed by free-ranging, adult male yellow baboons (Papio hamadryas cynocephalus) in Ruaha National Park, Tanzania are described. For each food I provide (1) the total number of grams consumed, (2) the total number of minutes used and (3) the estimated grams obtained per minute of handling. I hypothesize purposeful encounter for predictable foods that either use a relatively large proportion of feeding time or provide a relatively high number of grams per minute handling.

Testes Size and Body Weight in the Milne-Edwards’ Sifaka (Propithecus edwardsi) of Ranomafana National Park, Madagascar, Relative to Other Strepsirhine Primates

Pochron and Wright [2002] examined the relationship between testes volume (TV) and body weight in the Milne-Edwards’ sifaka (Propithecus edwardsi) and compared it to 18 captive strepsirhine primate species [Kappeler, 1997]. We reported a TV 206% larger than predicted, but our equation provided an overestimate by a factor of 8. Since then, we have doubled our morphology data from sifakas, and data from other strepsirhines have become available (Microcebus murinus [Fietz, 1999]; Phaner furcifer and others [Schülke et al., 2004]; Eulemur allbocollaris and E. fulvus rufus [Johnson et al., in revision]). Here we recalculate the TV of our sifaka relative to other strepsirhines using more sifaka data, more species and the correct formula.