34 The Ecological Perspective 6. Power and Powerlessness Abuse of power can be coercive, exploitative, or both. Coercive abuse of power is the withholding of power by dominant groups from vulnerable groups based upon personal and cultural characteristics such as race, ethnicity, gender, and sexual ori- entation. The oppression of vulnerable groups results in their continued margin- alization through institutionalized forms of racism, classism, sexism, ageism, het- erosexism, and other prejudices. Exploitative abuse of power by dominant groups leaves vulnerable populations at risk to their physical and mental health as a result of aging infrastructures and toxic environmental conditions, among other things. 7. Habitat and Niche The habitat of human beings consists of physical, natural, and social settings embedded in a cultural context. Niche refers to the position occupied by a spe- cies in a biotic community. When applied to human beings, the term refers to the status that individuals, families, groups, and communities occupy in their social environment. 8. Life Course This concept refers to the unique, nonpredictable pathways of development that humans take within diverse environments and cultures and their varied life experiences from conception and birth to old age. Life transitions are viewed not as isolated, fixed developmental stages, but rather as ongoing processes, occurring and recurring throughout the life course. The life course concept views human development and social functioning from the perspectives of historical, individual, and social time. Historical time refers to the various formative effects of social change on dif- ferent birth cohorts. Individual time refers to the experiences, attributes, mean- ings, and outcomes of personal and environmental factors over the course of one’s life within historical and cultural contexts. Social time reflects the transi- tions, rituals, and expectations that occur within groups with a shared identity. 9. Risk and Protective Factors, Resilience, and Adversarial Growth As social work is a profession rooted in empowerment and building upon client strengths, the need to identify factors that promote—or undermine—resilience