Session 4: Behavioral Ecology: Feeding

1.  Key Concepts:

In the lives of animals, including primates, the suite of behaviors associated with eating and avoiding being eaten figure prominently.  These behaviors include those set to identify quality food sources and habitat types, to thermoregulate, and to avoid predators.  Locomotion is a key component of these behaviors.

2.  Definitions & Terms:

Thermoregulation

The regulation of body temperature.

Distribution

The frequency of occurrence or the natural geographic range where a population or species occurs.

3.  Requirements of Primates: 

 “The whole of nature is a conjugation of the verb to eat, in the active and passive.” —William Ralph Inge (1860-1954)

 What does a primate need? 

• space (shelter/habitat)
• food
• predator avoidance skills
  
• thermoregulation and general maintenance
• reproduction
• social groups

 The variety of approaches primates species take to meet these common, basic needs is astounding. 

Habitat selection and utilization:

Consider the multiple variables of a habitat, especially the three dimensional aspect.  Primates must choose and utilize habitat types that meet their specific requirements for food acquisition, density, and more.  Things that must be considered include:

• Type of habitat, or ecozone

• Biotic makeup of the habitat
  
• Distributions and densities of food, space and other occupants
  
• The structural makeup of the habitat which can provide limits based on locomotory and utilization constraints
• Spatial organization of environment, including 3-D utilization and structural niches
• The ability to defend territory (or not), either core areas or entire home ranges
• Temporal patterns in utilization (daily range, seasonal variation, temporal variation)
• Cooperative/mutualistic utilization (intragroup use of space concepts)

4.  You are what you eat:  Food acquisition and processing:

Non-human primates interact with food sources in a completely distinct manner from humans.  Food source availability dictates the daily movement patterns of groups of primates.  The types of foods consumed determines the energy available for other activities and is related to group structure, mating patterns, morphology, and thermodynamics of primates.

Food sources include leafy material, fruits, seeds & nuts, exudates, insects, and other animal matter.

Leafy material:  Leafy material is the most common dietary element of primates.

Very abundant and evenly distributed. Low competition. Extremely variable quality of nutritional value; young leaves are the most nutritive. Mechanical digestion is low quality; over time, degradation occurs but this is not a good method for acquisition of nutrients. A measure of nutrient accessibility is ADF, or the acid digestion fiber, with high ADF values representing high nutrient food with easy access. Seasonality is a cost of leaf consumption, specifically regarding the leaf flush. Secondary compounds (tannins, alkaloids, etc.) contained in leaves can be toxic to primates.

Photo by Scott Chacon. Some rights reserved.

Fruits:  Primates love fruits because fruits are laden with sugar. 

Photo by wwarby. Some rights reserved.

Patchily spaced so can be variable in space and time. High nutritive return due to the simplicity in digesting. Easy processing, if ripe, with little need for even chewing. High competition.  Nothing has more competition than fruits. Seasonal availability.

Insects:

Consumption is second only to fruits for primates. Has extremely variable distribution because they can be tricky to catch and eat. High nutritive return but due to capture costs, very few primates. Capture costs can be extremely high. Variable processing costs.

Photo by Marko_Kivelä, Some rights reserved.

Seeds & nuts:

• Have a variable distribution.
• Have a very high nutritive return with very high processing costs due to the challenge in access and their high amount of secondary compounds. 
  
• Only some primates consume nuts and seeds, but those that do typically have unusual adaptations for accessing. 

Exudates (Tree Saps):

Tree saps have a fairly evenly distribution and have a high nutritive return.  However, the high extraction costs limit access to the non-human primates with specific dental modifications.  Thus, there are really a few competitors for exudates.

Other animal matter:

Very few primates consume mammals or other vertebrates, but some consume them opportunistically.  Macaques are willing to eat anything.  Animal matter is largely unreliable as a food source.  It is has a variable distribution, has variable capture costs, and variable nutrient return.

5.  Locomotion

Locomotory Challenges

include moving in variable environments.  Primates live terrestrially & arboreally, and many primate species use a mix of terrestrial and arboreal habitats.  Additionally, body size and structure limit movements.  Locomotion must optimize movements for food acquisition within these constraints.

Movement types

include leaping, walking, climbing, running, brachiating, armswinging, bridging, vertical clinging, and tail use (both prehensiled and non-prehensiled).

6.  Additional Material:

Primates in Perspective.  2007.  eds.  C. J. Campbell, A. Fuentes, K.C. MacKinnon, M. Panger, and S. K. Bearder.  Oxford University Press.

• Chapter 29: Primate Nutritional Ecology - Lambert
  
• Chapter 32:  Predation on Primates - Miller & Treves
  
• Chapter 33:  Primate Locomotor Behavior and Ecology - Garber