Using individual-based modeling to explore how environmental and anthropogenic factors impact piping plover breeding success

Alexander J Cohen, Purdue University

Abstract

The Piping Plover (Charadrius melodus) is an intensively managed shorebird species which breeds in part along the Atlantic Coast. Major threats to Piping Plovers include habitat loss and degradation, predation, human disturbance, and vulnerability to the elements. Common management techniques include predator exclosures and symbolic fencing around nests to deter humans from entering nesting areas. However, Piping Plover productivity is highly variable even with management. Many site- and season-specific factors affect plovers and their interactions with other inhabitants of the beach environment. Variability in magnitude and patterns of human disturbance, plover behavioral tolerance of disturbance, and a variety of beach characteristics may have important impacts on plover breeding success. Accounting for each of these factors, along with their interactions, is a difficult task empirically. However, simulation modeling tools allow for creation of virtual worlds and the ability to simultaneously manipulate factors of interest. In this thesis, I apply two individual-based modeling tools to explore how plover productivity (e.g. survival, energetics, and behavior) is determined by the functioning of individual plovers, as well as their interactions with individual humans and, in the second model, individual predators. For the first model application, I employed the individual-based model SODA (Simulation of Disturbance Activities) to explore the implications of human disturbance on plovers. I created digital representations of 15 Massachusetts beaches and measured relevant spatial characteristics (e.g. beach width, configuration of symbolic fencing). I then created 20 combinations of different scenarios for human disturbance levels and plover flush distances, and ran simulations for each beach and disturbance scenario. Model outputs included the amount of time adult plovers and chicks spent flushing, along with chick weights. For the second model application, I built a similar model in NetLogo which incorporated explicit virtual predators along with virtual humans. I created 15 virtual beach configurations which varied in characteristics including beach width, extent of symbolic fencing, presence or absence of a high-quality foraging area, and accessibility of that area (if present). I also created six scenarios for human recreational density, four sets of plover flush distances, three scenarios for predator abundance, and three sets of predator flush distances. I ran simulations using a fully crossed design. Model outputs included nest survival, chick survival, chick weights, and time adults spent flushed off nests. Results and implications were similar for each model. Human densities and plover flush distances were essential determinants of disturbance and subsequent risk of nest and chick predation. Beach width was an important determinant of how frequently humans disturbed plovers, and also influenced nest and chick survival by moderating predator search efficiency. Symbolic fencing effectively reduced disturbance, though configuration of fencing was more important than total area fenced, and extra fencing reduced chick survival by increasing contact with humans and predators in intertidal foraging areas. When high-quality foraging areas were present, and as those areas became more accessible, chick foraging efficiency and survival increased. Overall, the modeling framework allowed investigation and manipulation of multiple important factors in the beach environment. Based on model results, I make several recommendations for site-specific Piping Plover management.

Degree

M.S.

Advisors

Zollner, Purdue University.

Subject Area

Wildlife Conservation|Ecology|Conservation

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