3.0 CONCEPTUAL ECOLOGICAL MODELS (Scott and Eckert)

A conceptual ecological model is presented in Figure 1 to summarize how natural and 

human drivers interact with key structural and functional elements of ecosystems that 

span the US/Mexico border-region. This model focuses on natural resource assets of 

concern to resource managers and the public, as well as how illegal border activities, 

border security infrastructure and enforcement interact with natural disturbance processes 

to influence border ecosystems. The model further links select ecosystem structural and 

functional attributes to specific physical and biological metrics, which can be used to 

monitor change in resource condition over time. 

An ecosystem is a spatially defined unit of the Earth that includes all organisms, along 

with all components of the physical environment within its boundaries (Christensen et al. 

1996). Ecosystem structure includes the types, amounts, and spatial arrangement of 

physical and biological elements of an ecosystem. Ecosystem functioning refers to flows 

of energy and materials through biological and physical components of an ecosystem. 

Functional processes include stream flow and related channel change processes, hillslope 

runoff and erosion, nutrient cycling, and the production, retention and decomposition of 

organic material (Díaz and Cabido 2001). A complete list of ecosystem structural and 

functional elements is provided in Appendix 1. A driver is any natural or human-induced 

factor that directly or indirectly causes a change in an ecosystem (Carpenter et al. 2006). 

Important physical and biological drivers include climate change, extreme weather 

events, land conversion, diseases and invasive species. Ecosystems and resource 

conditions are not static. They change within a natural range of variation, while 

maintaining structural and functional integrity, in response to natural drivers like climate 

variability. This natural range of variation is represented in Figure 1 by the shifting edges 

and dashed arrows associated with ecosystem elements as well as resource condition 

metrics. Any long-term ecological resource monitoring effort must be done with an 

understanding of the natural range of variation in an ecosystem.

Figure 2 depicts the conceptual ecological model in the context of project design and 

implementation. Monitoring design draws upon key ecosystems and ecosystem elements 

to identify study areas and define study design. Specific monitoring protocols developed 

and refined in the context of monitoring design for the measurement of specific resource 

metrics. Monitoring implementation produces quantitative data on resource condition. 

These data will need to be managed and archived so that they can be analyzed and used 

to report on the direction and magnitude of change in resource condition over time. The 

project design process is consistent with an adaptive management framework whereby

monitoring is used to evaluate and refine the effectiveness of management actions on 

resource condition.
Figure 1. A conceptual ecological model representing US/Mexico border ecosystems and related physical and biological metrics 

(orange ellipse), which could be used to monitor change in resource condition over time. Ecosystem structural and functional 

elements (green ellipse) interact dynamically with natural and human drivers (blue ellipses) of ecosystem change. Ecosystem 

elements and condition metrics vary over time in response to natural drivers (dashed arrows).

REGIONAL CLIMATE &

NATURAL DISTURBANCES

DIRECT BORDER FENCE EFFECTS

RECREATION & UNDOCUMENTED ALIENS

BORDER SECRUITY INFRASTRUCTURE

ENFORCEMENT ACTIVITIES

LIVESTOCK GRAZING

WILDLAND FIRE

INVASIVE SPECIES

(e.g., Precipitation, temperature, 

drought & storms)

HUMAN DRIVERS NATURAL DRIVERS

ECOSYSTEM STRUCTURAL 

AND FUNCTIONAL ELEMENTS

RESOURCE CONDITION METRICS

CATCHMENT CHARACTERISTICS

HYDROLOGIC

GEOMORPHIC

BIOGEOCHEMICAL

HABITAT STRUCTURE, ARRANGEMENT & CONNECTIVITY

VEGETATION CHARACTERISTICS

POPULATION DYNAMICS

SPECIES OF CONCERN

CULTURAL

CHANGE IN HILLSLOPE RUNOFF AND EROSION

CHANGE IN EROSION OF CHANNEL BED AND BANKS

CHANNEL AGGRADATION

CHANGE IN FLOODING

CHANGE IN WILDLAND FIRES

CHANGE IN DIVERSITY OF NATIVE SPECIES

CHANGE IN COVER OF NATIVE VEGETATION

CHANGE IN COVER OF NON-NATIVE VEGETATION
Figure 2. The relationship of monitoring design, implementation, and data management, analysis and reporting to border 

ecosystems and selected resource condition metrics. 

RESOURCE CONDITION METRICS

HUMAN 

DRIVERS

NATURAL 

DRIVERS

ECOSYSTEM STRUCTURAL 

AND FUNCTIONAL 

ELEMENTS

MONITORING DESIGN

EXPERIMENTAL DESIGN

STUDY AREAS

MONITORING PROTOCOLS

DATA ANALYSIS AND 

REPORTING

DATA MANAGEMENT 

AND ARCHIVING

ASSESSMENTS OF RESOURCE 

CONDITION

MEASUREMENT OF RESOURCE 

METRICS